Engineering the glycogen metabolism in cyanobacterial photosynthetic cell factories: a review / 生物工程学报

Cyanobacteria are important photosynthetic autotrophic microorganisms and are considered as one of the most promising microbial chassises for photosynthetic cell factories. Glycogen is the most important natural carbon sink of cyanobacteria, playing important roles in regulating its intracellular carbon distributions. In order to optimize the performances of cyanobacterial photosynthetic cell factories and drive more photosynthetic carbon flow toward the synthesis of desired metabolites, many strategies and approaches have been developed to manipulate the glycogen metabolism in cyanobacteria. However, the disturbances on glycogen metabolism usually cause complex effects on the physiology and metabolism of cyanobacterial cells. Moreover, the effects on synthesis efficiencies of different photosynthetic cell factories usually differ. In this manuscript, we summarized the recent progress on engineering cyanobacterial glycogen metabolism, analyzed and compared the physiological and metabolism effects caused by engineering glycogen metabolism in different cyanobacteria species, and prospected the future trends of this strategy on optimizing cyanobacterial photosynthetic cell factories.

Responses of antioxidant enzymes, photosynthetic pigments and carbohydrates in micropropagated Pitcairnia encholirioides L.B. Sm. (Bromeliaceae) under ex vitro water deficit and after rehydration / Respostas de enzimas antioxidantes, pigmentos fotossintéticos e carboidratos em Pitcairnia encholirioides L.B. Sm. (Bromeliaceae) micropropagadas, sob déficit hídrico ex vitro e após reidratação

Abstract In this study, the activities of antioxidant enzymes, photosynthetic pigments, proline and carbohydrate contents in Pitcairnia encholirioides under ex vitro conditions of water deficit were evaluated. Results show that plants under progressive water stress, previously in vitro cultured in media supplemented with 30 g L-1 sucrose and GA3, accumulated more proline and increased peroxidase (POD) activity and the contents of photosynthetic pigments and carbohydrates. For plants previously in vitro cultured with 15 g L-1 sucrose and NAA, no differences were found for proline content and there were reductions in activities of peroxidase (POD), catalase (CAT) and poliphenoloxidase (PPO), and in contents of carbohydrates, with progress of ex vitro water deficit. After rehydration, plants showed physiological recovery, with enzymatic activities and contents of metabolites similar to those found in the controls not submitted to dehydration, regardless of the previous in vitro culture conditions. These results show that micropropagated P. encholirioides has high tolerance to dehydration once in ex vitro conditions, which can ensure the survival of plants from tissue culture when transferred to its natural environment, emphasizing the importance of such biotechnology for the propagation of endangered species.

Resumo Neste estudo, foram avaliadas as atividades de enzimas antioxidantes, pigmentos fotossintéticos, conteúdo de prolina e carboidratos em Pitcairnia encholirioides sob déficit hídrico em condições ex vitro. Os resultados mostraram que as plantas sob estresse hídrico progressivo, previamente cultivadas in vitro em meio de cultura suplementado com 30 g L-1 de sacarose e GA3 acumularam mais prolina e aumentaram a atividade da peroxidase (POD) e os teores de pigmentos fotossintéticos e carboidratos. Para plantas previamente cultivadas in vitro com 15 g L-1 de sacarose e ANA, não foram encontradas diferenças nos conteúdos de prolina e houve reduções nas atividades da peroxidase (POD), catalase (CAT) e polifenoloxidase (PPO), e no conteúdo de carboidratos, com o progresso do déficit hídrico ex vitro. Após a reidratação, as plantas apresentaram recuperação fisiológica, com atividades enzimáticas e conteúdo de metabólitos semelhantes aos encontrados nos controles não sujeitos à desidratação, independentemente das condições de cultivo in vitro. Estes resultados mostram que P. encholirioides micropropagada tem alta tolerância à desidratação uma vez em condições ex vitro, o que pode garantir a sobrevivência de plantas provenientes da cultura de tecidos quando transferidas para seu ambiente natural, enfatizando a importância desta biotecnologia para a propagação de espécies ameaçadas.

Plant morphology, physiological characteristics, accumulation of secondary metabolites and antioxidant activities of Prunella vulgaris L. under UV solar exclusion

BACKGROUND: Prunella vulgaris L. has been an important medicinal plant for the treatment of thyroid gland malfunction and mastitis in China for over 2000 years. There is an urgent need to select effective wavelengths for greenhouse cultivation of P. vulgaris as light is a very important factor in P. vulgaris growth. Here, we described the effects of natural light (control) and UV solar exclusion on the morphological and physiological traits, secondary metabolites contents and antioxidant activities of P. vulgaris. RESULTS: The results showed that UV solar exclusion resulted in remarkable alterations to morphological and biomass traits; significantly reduced the chlorophyll a, chlorophyll b and total chlorophyll contents; significantly enhanced the ratio of chlorophyll a to b; and significantly increased the carotenoid and anthocyanin contents in P. vulgaris. UV solar exclusion significantly increased the catalase (CAT) and peroxidase (POD) activities, increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities and slightly decreased the glutathione (GSH) content. UV solar exclusion significantly increased the soluble sugar and H2O2 contents and increased the soluble protein content but significantly decreased the proline content and slightly decreased the MDA content. The secondary metabolite contents (total phenolics, rosmarinic acid, caffeic acid, hyperoside, ursolic acid and oleanolic acid) and in vitro antioxidative properties (DPPH· and ABTS·+scavenging activities) were significantly increased in P. vulgaris spicas under UV solar exclusion. Additionally, the total polysaccharide and total flavonoids contents were slightly increased by UV solar exclusion. The salviaflaside content was significantly reduced by UV solar exclusion. CONCLUSION: Our study demonstrated that P. vulgaris activates several antioxidant defence systems against oxidative damage caused by UV solar exclusion.

Desiccation tolerance in the Antarctic moss Sanionia uncinata

BACKGROUND: One of the most extreme environments on our planet is the Maritime Antarctic territory, due to its low-water availability, which restricts the development of plants. Sanionia uncinata Hedw. (Amblystegiaceae), the main colonizer of the Maritime Antarctic, has effective mechanisms to tolerate this environment. It has been described that the tolerance to desiccation is mediated by the hormone abscisic acid (ABA), antioxidants systems, accumulation of compatible solutes and proteins of the late embryogenesis abundant (LEA). However, to date, these mechanisms have not been described in S. uncinata. Therefore, in this work, we postulate that the tolerance to desiccation in the Antarctic moss S. uncinata is mediated by the accumulation of ABA, the osmolytes proline and glycine betaine, and dehydrins (an LEA class 11 proteins). To demonstrate our hypothesis, S. uncinata was subjected to desiccation for 24 h (loss in 95% of water content), and the effects on its physiological, photosynthetic, antioxidant and biochemical parameters were determined. RESULTS: Our results showed an accumulation of ABA in response to water loss, and the activation of protective responses that involves an increment in levels of proline and glycine betaine, an increment in the activity of antioxidant enzymes such as SOD, CAT, APX and POD, and the accumulation of dehydrins proteins. CONCLUSION: The results showed, suggest that S. uncinata is a desiccation-tolerant moss, property mediated by high cellular plasticity regulated by ABA.

Cadmium tolerance of Typha domingensis Pers. (Typhaceae) as related to growth and leaf morphophysiology / A tolerância ao cádmio por Typha domingensis Pers. (Typhaceae) correlacionada com o crescimento e a morfofisiologia foliar

Abstract Typha domingensis (cattail) is a native macrophyte known by its capacity to tolerate several heavy metals effects and the potential use for phytoremediation. However, in despite that cadmium (Cd) is one of the most toxic pollutants; its effects in T. domingensis biology remain uninvestigated. Thus, the objective of this study was to study the tolerance of T. domingensis to cadmium contamination by evaluating its growth, Cd uptake, leaf anatomy and gas exchange. The experiment was designed using three cadmium concentrations (0, 10 and 50 µM) and ten replicates for 90 days. The cadmium uptake, growth, gas exchange, chlorophyll content and leaf anatomy were evaluated. Data was submitted to ANOVA and Scott-Knott test for P<0.05. Typha domingensis accumulates Cd proportionally to its concentration on the solution and the content of this metal was higher in roots as compared to shoots. Plants showed no significant modifications on growth parameters such as the biomass production, number of leaves, number of clones and the biomass allocation to organs. The photosynthesis, transpiration and chlorophyll content were not modified by Cd. Most anatomical traits evaluated were not modified by the metal but the stomatal density and the proportion of vascular tissues were reduced under 50 µM of Cd. In despite, the leaf anatomy showed no toxicity evidences for any Cd level. The absence of growth reduction and the stability of anatomical and physiological traits give insight about the Cd tolerance of this species. Therefore, T. domingensis is able to overcome Cd toxicity and shows potential for phytoremediation.

Resumo A espécie Typha domingensis (taboa) é uma macrófita nativa conhecida por sua tolerância a vários metais pesados e potencial uso na fitorremediação. Contudo, apesar de que o Cd é um dos poluentes mais tóxicos; Seus efeitos em T. domingensis ainda não foram investigados. Assim, o objetivo desse estudo foi avaliar a tolerância de T. domingensis ao cádmio, avaliando o crescimento, absorção de Cd, anatomia foliar e trocas gasosas. O experimento foi conduzido utilizando três concentrações de Cd (0, 10 e 50 µM) e dez repetições por 90 dias.. O crescimento, trocas gasosas e o teor de clorofila e anatomia foliar foram avaliados. Os dados foram submetidos à ANOVA e ao teste de Scott-Knott para P<0,05. A absorção de cádmio, crescimento, trocas gasosas, teor de clorofila e anatomia foliar foram analisados. As plantas de T. domingensis podem acumular Cd proporcionalmente à sua concentração na solução e o teor deste metal foi maior nas raízes em comparação com a parte aérea. As plantas não apresentam modificações significativas nos parâmetros de crescimento como produção de biomassa, número de folhas, número de clones produzidos e alocação de biomassa nos órgãos. A fotossíntese, transpiração e conteúdo de clorofila não foram afetados de forma significativa pelo Cd. A maioria das características anatômicas avaliadas não apresentou diferenças, mas houve redução na densidade estomática e na proporção de tecidos vasculares na concentração de 50 µM de Cd. A anatomia foliar não mostrou evidências de toxicidade em nenhum dos níveis de Cd. A ausência de redução de crescimento e estabilidade das características anatômicas e fisiológicas caracteriza alta tolerância da espécie ao Cd. Portanto, T. domingensis é capaz de superar a toxicidade do Cd e demostra potencial para fitorremediação.

Photosynthetic capacity and water use efficiency in Ricinus communis (L) under drought stress in semi-humid and semi-arid areas

ABSTRACT Castor bean is one of the crops with potential to provide raw material for production of oils for biodiesel. This species possess adaptive mechanisms for maintaining the water status when subjected to drought stress. A better understanding these mechanisms under field conditions can unravel the survival strategies used by this species. This study aimed to compare the physiological adaptations of Ricinus communis (L.) in two regions with different climates, the semi-arid and semi-humid subject to water stress. The plants showed greater vapor pressure deficit during the driest hours of the day, which contributed to higher values of the leaf temperature and leaf transpiration, however, the VPD(leaf-air) had the greatest effect on plants in the semi-arid region. In both regions, between 12:00 p.m. and 2:00 p.m., the plants presented reduction in the rates of photosynthesis and intracellular CO2 concentration in response to stomatal closure. During the dry season in the semi-arid region, photoinhibition occurred in the leaves of castor bean between 12:00 p.m. and 2:00 p.m. These results suggest that castor bean plants possess compensatory mechanisms for drought tolerance, such as: higher stomatal control and maintenance of photosynthetic capacity, allowing the plant to survive well in soil with low water availability.

Growth, photosynthetic pigments and production of essential oil of long-pepper under different light conditions

ABSTRACT Piper hispidinervum C. DC. is popularly known as long-pepper and it owns a commercial value due to the essential oil it produces. Long-pepper oil is rich in safrole and eugenoln components that have insecticidal, fungicidal and bactericidal activity. It has been establish that to medicinal plants light influences not only growth but also essential oil production. The growth, the content of photosynthetic pigments and the essential oil production of Piper hispidinervum at greenhouses with different light conditions was evaluated. The treatments were characterized by cultivation of plants for 180 days under different light conditions, produced by shading greenhouses with 50% and 30% of natural incident irradiance, two colored shading nets red (RN) and blue (BN) both blocking 50% of the incident radiation and one treatment at full-sun (0% of shade). The results showed that the treatments of 50% shade and RN and BN were the ones which stimulated the greater growth. Blue and red light also had the best production of photosynthetic pigments. Essential oil yielded more under full sun therefore this is the most indicated condition to produce seedlings for the chemical and pharmaceutical industry.

Partitioning of the diffuse attenuation coefficient for photosynthetically available irradiance in a deep dendritic tropical lake

ABSTRACT We studied the effects of particulate and dissolved optically active components on the attenuation of photosynthetic active radiation (PAR) in a tropical lake. The temporal and spatial distribution of tripton, Chl-a and aCDOM(440) and their relative contribution to the diffuse PAR attenuation coefficient (Kd) was investigated at 21 sites (dry and wet seasons and two intermediate periods) and at monthly interval at 1 pelagic site. Higher values of ​​ Kd were observed during the mixing period, characterized by a higher concentration of tripton and Chl-a compared to the stratified rainy season. In the spatial sampling PAR attenuation was dominated by tripton absorption/scattering (average relative contribution of 79%), followed by Chl-a (average 11.6%). In the monthly sampling tripton and Chl-a accounted for most of the Kd with relative contributions of 47.8% and 35.6%, respectively. Multiple linear regression analysis showed that Chl-a and tripton in combination explained 97% of the monthly variation in Kd (p<0.001), but Chl-a had more influence (higher regression coefficient). Thus, although most of light attenuation was due to tripton, seasonal variations in phytoplankton abundance were responsible for most of the temporal fluctuations in Kd.

Effects of flooding stress in tomato plants transformed with different levels of mitochondrial sHSP23 6 / Efeitos do estresse por alagamento em plantas de tomateiro transformada com diferentes níveis de sHSP23 6 mitocondrial

Abstract Soil flooding is an environmental stressor for crops that can affect physiological performance and reduce crop yields. Abiotic stressors cause changes in protein synthesis, modifying the levels of a series of proteins, especially the heat shock proteins (HSP), and these proteins can help protect the plants against abiotic stress. The objective of this study was to verify if tomato plants cv. Micro-Tom from different genotypes with varying expression levels of MT-sHSP23.6 (mitochondrial small heat shock proteins) have different responses physiological to flooding. Plants from three genotypes (untransformed, MT-sHSP23.6 sense expression levels and MT-sHSP23.6 antisense expression levels) were cultivated under controlled conditions. After 50 days, the plants were flooded for 14 days. After this period half of the plants from each genotype were allowed to recover. Chlorophyll fluorescence, gas exchange, chlorophyll index, leaf area and dry matter were evaluated. Flood stress affected the photosynthetic electron transport chain, which is related to inactivation of the oxygen-evolving complex, loss of connectivity among units in photosystem II, oxidation-reduction of the plastoquinone pool and activity of photosystem I. The genotype with MT-sHSP23.6 sense expression levels was less sensitive to stress from flooding.

Resumo O alagamento do solo é um estressor ambiental para as culturas e pode afetar o desempenho fisiológico e reduzir a produtividade das culturas. Estresses abióticos causam mudanças na síntese de proteínas, modificando os níveis de uma série de proteínas, em especial as proteínas de choque térmico (HSP) e essas proteínas são conhecidas por proteger as plantas contra estresses abióticos. O objetivo deste estudo foi verificar se as plantas do tomateiro cv. Micro-Tom de distintos genótipos com diferentes níveis de expressão da MT-sHSP23.6 (proteínas mitocondriais de choque térmico com pequena massa molecular), têm diferentes respostas fisiológicas ao alagamento. As plantas de três genótipos (não-transformado, transformado com orientação antisense e transformado com orientação sense para MT-sHSP23.6) foram cultivadas sob condições controladas. Após 50 dias as plantas foram alagadas durante 14 dias. Após esse período as plantas de cada genótipo foram recuperadas. Foram avaliados fluorescência da clorofila, trocas gasosas, índice de clorofila, área foliar e massa seca. O estresse por alagamento afetou a cadeia de transporte de elétrons da fotossíntese, que está relacionado à inativação do complexo de evolução do oxigênio, perda da conectividade entre as unidades do fotossistema II, de oxidação e redução do pool de plastoquinona e atividade do fotossistema I. O genótipo com orientação sense MT-sHSP23.6 foi menos sensível ao estresse por alagamento.

Photosynthesis at the far-red region of the spectrum in Acaryochloris marina

Acaryochloris marina is an oxygenic cyanobacterium that utilizes far-red light for photosynthesis. It has an expanded genome, which helps in its adaptability to the environment, where it can survive on low energy photons. Its major light absorbing pigment is chlorophyll d and it has α-carotene as a major carotenoid. Light harvesting antenna includes the external phycobilin binding proteins, which are hexameric rods made of phycocyanin and allophycocyanins, while the small integral membrane bound chlorophyll binding proteins are also present. There is specific chlorophyll a molecule in both the reaction center of Photosystem I (PSI) and PSII, but majority of the reaction center consists of chlorophyll d. The composition of the PSII reaction center is debatable especially the role and position of chlorophyll a in it. Here we discuss the photosystems of this bacterium and its related biology.

Molecular and functional characterization of ferredoxin NADP(H) oxidoreductase from Gracilaria chilensis and its complex with ferredoxin

BACKGROUND: Ferredoxin NADP(H) oxidoreductases (EC 1.18.1.2) (FNR) are flavoenzymes present in photosynthetic organisms; they are relevant for the production of reduced donors to redox reactions, i.e. in photosynthesis, the reduction of NADP+ to NADPH using the electrons provided by Ferredoxin (Fd), a small FeS soluble protein acceptor of electrons from PSI in chloroplasts. In rhodophyta no information about this system has been reported, this work is a contribution to the molecular and functional characterization of FNR from Gracilaria chilensis, also providing a structural analysis of the complex FNR/Fd. METHODS: The biochemical and kinetic characterization of FNR was performed from the enzyme purified from phycobilisomes enriched fractions. The sequence of the gene that codifies for the enzyme, was obtained using primers designed by comparison with sequences of Synechocystis and EST from Gracilaria. 5'RACE was used to confirm the absence of a CpcD domain in FNRPBS of Gracilaria chilensis. A three dimensional model for FNR and Fd, was built by comparative modeling and a model for the complex FNR: Fd by docking. RESULTS: The kinetic analysis shows KMNADPH of 12.5 M and a kcat of 86 s-1, data consistent with the parameters determined for the enzyme purified from a soluble extract. The sequence for FNR was obtained and translated to a protein of 33646 Da. A FAD and a NADP+ binding domain were clearly identified by sequence analysis as well as a chloroplast signal sequence. Phycobilisome binding domain, present in some cyanobacteria was absent. Transcriptome analysis of Gch revealed the presence of two Fd; FdL and FdS, sharing the motif CX5CX2CX29X. The analysis indicated that the most probable partner for FNR is FdS. CONCLUSION: The interaction model produced, was consistent with functional properties reported for FNR in plants leaves, and opens the possibilities for research in other rhodophyta of commercial interest.

Biomass allocation and gas exchange are affected by light conditions in endangered Cedrela salvadorensis (Meliaceae) seedlings / Asignación de biomasa e intercambio de gases son afectados por las condiciones de luz en plántulas de Cedrela salvadorensis (Meliaceae) en peligro de extinción

Abstract:The determination of favorable light habitat conditions per species and life stage is transcendental, for both ex situ and in situ conservation strategies of endangered forest tree species, and for their utilization as plantation trees. This becomes especially important when planting material is scarce. We studied the multivariate responses in biomass allocation and in gas exchange to light and to CO2 in Cedrela salvadorensis seedlings, grown under similar light conditions as those this species faces in nature. During a period of 135 days, groups of ten seedlings were put under 75, 45, 15 and 3.5 % of full sun exposure obtained with neutral shade cloth, under nursery conditions. A series of biomass allocation variables and detailed gas exchange parameters (photosynthesis response curves to light and to internal carbon concentration) were measured at the end of the growth period in plants of the four treatments. According to the principal component analyses, highest values of gas exchange response were associated with the lower values of biomass allocation traits. These changes can be associated with resource-conservative and resource-acquisitive strategies, where the C. salvadorensis seedlings acclimatize their traits for the exploration and exploitation of light, to high or to dim light environment, respectively. The multivariate analyses also showed that the plants had a high performance at 45 % of light environments. These results suggest that 45 % of light environment was the optimal light habitat of this species at the tested developing stage. Our results have important implications to choose the best natural habitat for a successful establishment of C. salvadorensis. We propose practical considerations for programs of reforestation or reintroduction where this species be involved. Rev. Biol. Trop. 64 (3): 1143-1154. Epub 2016 September 01.

ResumenLa determinación de las condiciones lumínicas favorables por especie y estado de vida es trascendental para las estrategias de conservación ex situ y in situ de especies de árboles en peligro de extinción, y su utilización como plantaciones forestales. Esto se vuelve especialmente importante cuando el material de siembra es escaso. Aquí, nosotros estudiamos las respuestas en asignación de biomasa y en intercambio de gases a luz y CO2 en plántulas de Cedrela salvadorensis crecidas bajo condiciones lumínicas similares a las que esta especie enfrenta en la naturaleza. Durante 135 días, grupos de diez plántulas fueron colocadas bajo condiciones de 75, 45, 15 y 3.5 % de exposición total al sol obtenidas por medio de sarán bajo condiciones de vivero. Una serie de variables de asignación de biomasa y parámetros de intercambio de gases (fotosíntesis según curvas de respuesta a la luz y a la concentración de carbono interno) fueron medidas al final del periodo de crecimiento en las plantas de los cuatro tratamientos. De acuerdo con los análisis de componentes principales, valores altos de respuesta de intercambio de gases están asociados con valores bajos de rasgos de asignación de biomasa. Los cambios observados se encuentran asociados con las estrategias recurso-conservativas y recurso-adquisitivas donde C. salvadorensis aclimata sus rasgos para la exploración y explotación de luz en ambientes con escasa o excesiva radiación lumínica, respectivamente. Los análisis multivariados muestran también que las plantas tienen un alto rendimiento a 45 % de luz ambiental. Estos resultados sugieren que el 45 % de ambiente lumínico es el hábitat lumínico óptimo de esta especie en el estado de desarrollo estudiado. Nuestros resultados tienen importantes implicaciones para escoger el mejor hábitat natural para un exitoso establecimiento de C. salvadorensis. Por esto, proponemos consideraciones prácticas para programas de reforestación y reintroducción donde esta especie estaría involucrada.

The antioxidative defense system is involved in the premature senescence in transgenic tobacco (Nicotiana tabacum NC89)

BACKGROUND: α-Farnesene is a volatile sesquiterpene synthesized by the plant mevalonate (MVA) pathway through the action of α-farnesene synthase. The α-farnesene synthase 1 (MdAFS1) gene was isolated from apple peel (var. white winterpearmain), and transformed into tobacco (Nicotiana tabacum NC89). The transgenic plants had faster stem elongation during vegetative growth and earlier flowering than wild type (WT). Our studies focused on the transgenic tobacco phenotype. RESULTS: The levels of chlorophyll and soluble protein decreased and a lower seed biomass and reduced net photosynthetic rate (Pn) in transgenic plants. Reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and superoxide radicals (O2._) had higher levels in transgenics compared to controls. Transgenic plants also had enhanced sensitivity to oxidative stress. The transcriptome of 8-week-old plants was studied to detect molecular changes. Differentially expressed unigene analysis showed that ubiquitin-mediated proteolysis, cell growth, and death unigenes were upregulated. Unigenes related to photosynthesis, antioxidant activity, and nitrogen metabolism were downregulated. Combined with the expression analysis of senescence marker genes, these results indicate that senescence started in the leaves of the transgenic plants at the vegetative growth stage. CONCLUSIONS: The antioxidative defense system was compromised and the accumulation of reactive oxygen species (ROS) played an important role in the premature aging of transgenic plants.

Effects of different water management options and fertilizer supply on photosynthesis, fluorescence parameters and water use efficiency of Prunella vulgaris seedlings

BACKGROUND: Prunella vulgaris L. is a medical plant cultivated in sloping, sun-shaded areas in China. Recently, owing to air-environmental stress, especially drought stress strongly inhibits plant growth and development, the appropriate fertilizer supply can alleviate these effects. However, these is little information about their effects on P. vulgaris growing in arid and semi-arid areas with limited water and fertilizer supply. RESULTS: In this study, water stress decreased the photosynthetic pigment contents, inhibited photosynthetic efficiency, induced photodamage in photosystem 2 (PS2), and decreased leaf instantaneous WUE (WUEi). The decreased net photosynthetic rate (Pn) under medium drought stress compared with the control might result from stomatal limitations. However, fertilizer supply improved photosynthetic capacity by increasing the photosynthetic pigment contents and enhancing photosynthetic efficiency under water deficit. Moreover, medium fertilization also increased WUEi under the two water conditions, but fertilizer supply did little to alleviate the PS2 photodamage caused by drought stress. Hence, drought stress was the primary limitation in the photosynthetic process of P. vulgaris seedlings, while the photosynthetic characteristics of the seedlings exhibited positive responses to fertilizer supply. CONCLUSIONS: Appropriate fertilizer supply is recommended to improve photosynthetic efficiency, enhance WUEi and alleviate photodamage under drought stress.

Origin of the subepidermal tissue in Piper L. leaves / Origem do tecido subepidérmico em folhas de Piper L.

Studies on the anatomy of Piper leaves demonstrate the presence of a subepidermal tissue distinct from the adjacent epidermis, which cells show thin walls and hyaline contents. Some authors consider such cells a hypodermal tissue, while others refer to them as components of a multiple epidermis. In this study, the nature of this subepidermal tissue was investigated through the analysis of leaf ontogeny in three Piper species. The analysis showed that the referred tissue originates from the ground meristem and, thus, should be considered a hypodermis. The studied species suggests that the role of the hypodermis would be to protect the photosynthetic apparatus from excess light, regulating the intensity of light reaching the chlorophyll parenchyma.

Os estudos de anatomia foliar de espécies de Piper revelam a presença de um tecido subepidérmico distinto da epiderme e cujas células apresentam paredes finas e conteúdo hialino. Estas células são referenciadas por alguns autores como um tecido hipodérmico e por outros, como sendo constituintes de uma epiderme múltipla. Nesse estudo verificou-se a natureza deste tecido subepidérmico a partir da análise da ontogênese foliar de três espécies de Piper. A análise revelou que o referido tecido tem origem do meristema fundamental e, portanto, deve ser denominado de hipoderme. Para as espécies avaliadas, sugere-se que a hipoderme teria função de, proteger o aparato fotossintético do excesso de luminosidade, regulando a intensidade luminosa que atinge o parênquima clorofiliano.

Acclimation of seedlings of Gnetum leyboldii Tul. Gnetaceae to light changes in a tropical rain forest / Aclimatación de plántulas de Gnetum leyboldii Tul. Gnetaceae a los cambios de luz en un bosque lluvioso tropical

The neotropical liana Gnetum leyboldii Gnetaceae is a gymnosperm that resembles angiosperms in wood anatomy, overall morphology, and seed dispersal mechanism. Like other woody lianas, seedlings germinate in the shaded forest understory and start climbing towards the canopy, being eposed to sites with etreme differences in light conditions. However, the etent of physiological and structural adjustment to contrasting light conditions in the early regeneration stages of Gnetum is unknown. To answer this question, we analyzed seedling growth and photosynthetic responses using a common garden eperiment with two light regimes: full sun and low light 20 of full sun at La Selva Biological Station, Costa Rica. We also characterized the germination pattern of this species. We monitored one and half-month old seedlings for four months. Leaf structure finely adapted to light treatments, but gas echange properties were buffered by large seed reserves, which dominated biomass distribution about 50 of the total biomass, followed by stem 27, leaf 16 and root biomass 6 across light conditions. The presence of large seeds and the low photosynthetic rates of seedlings in both environments show that G. leyboldii is specialized to eploit deep shade. More research is needed to determine if the patterns found in G. leyboldii are typical of similar lianas that initially eploit deep-shaded understories in their ascension to the canopy.

La liana neotropical Gnetum leyboldii Gnetaceae es una gimnosperma que se asemeja a las angiospermas en la anatomía de la madera, morfología general de la planta y mecanismo de dispersión de semillas. Al igual que otras lianas leñosas, las plántulas se regeneran en el sotobosque bajo dosel cerrado y eventualmente ascienden hacia el dosel, eplotando sitios con diferencias etremas en condiciones lumínicas. Se desconoce el grado de ajuste fisiológico a condiciones lumínicas contrastantes en las primeras fases de regeneración de Gnetum. Para contestar esta pregunta, analizamos las respuestas de crecimiento de las plántulas a ambientes contrastantes de luz de sol y sombra en un jardín común con condiciones de alta cielo abierto y baja luminosidad 20 del ambiente de sol en la Estación Biológica La Selva, Costa Rica. También caracterizamos su patrón de germinación. Monitoreamos plántulas de 1.5 meses de edad por 4 meses. La estructura foliar mostró una fina adaptación a los tratamientos de luz, pero las propiedades de intercambio gaseoso no cambiaron sino que fueron amortiguadas por las reservas de las semillas grandes, las cuales dominaron la distribución de biomasa aproimadamente 50 de la biomasa total seguidas por el tallo 27, la hoja 16 y raíces 6. El tener semillas grandes y plántulas con bajas tasas fotosintéticas muestra que G. leyboldii en su etapa de plántula está adaptado para eplotar la sombra profunda. Se requiere más investigación para determinar si los patrones encontrados en G. leyboldii son típicos de otras lianas que inicialmente eplotan la sombra profunda en su ascensión al dosel.

Structural adaptations of two sympatric epiphytic orchids (Orchidaceae) to a cloudy forest environment in rocky outcrops of Southeast Brazil / Adaptaciones estructurales de dos orquídeas epífitas simpátricas (Orchidaceae) en un bosque nuboso de un campo rupestre del sureste de Brasil

The survival of plants in epiphytic environments depends on vegetative adaptations capable to defraud different stresses. Based on the structural diversity of the Orchidaceae, the current study has the objective of relating the anatomical structure of Dichaea cogniauxiana and Epidendrum secundum with the distinct environments where they live. It was expected that, despite structural similarities as strategies for resource acquisition, some peculiar variations related to the distinct light microenvironments (inside or in the edge of the nebular forest, near to “campo rupestre” area) might be found. Leaves and roots of both species were collected in a nebular forest located at a “campo rupestre” area at Serra da Piedade, Brazil), in January and February 2005. D. cogniauxiana is adhered to trunks, in sites with high atmospheric humidity and shaded, while E. secundum is located at the edge of the nebular forest, in more luminous sites. The leaves of E. secundum had thicker cuticle and higher number of stomata per area than those of D. cogniauxiana, characteristics coherent with their distinct pattern of exhibition to sun light. The suprastomatic chambers formed by the thicker cuticle may function as a barrier of resistance to water evaporation. The succulence of the leaves of E. secundum propitiates organic acids storage at night, and the storage of starch may be involved in PEP-carboxylase metabolism, both propitiating CAM mechanism. Roots with larger number of cell layers of the velamen, and specialized thick walled cortical cells (both in E. secundum) help water absorption and indicate better adaptation to an environment with intense solar radiation and a probable higher water deficit. The remarkable cell wall thickening of E. secundum exodermis can confer more efficient protection against the excess of transpiration at the border of the nebular forest. On the other hand, besides D. cogniauxiana be epiphyte, it is in a low position - in a shaded environment and with high relative humidity. Its thin thickened velamen permits the entrance of the low available light, and photosynthesis, producing oxygen and helping to avoid hypoxia condition. As features registered for D. cogniauxiana and E. secundum roots, we can depict the velamen, distinct exodermis and endodermis, and specialized thick walled cortical cells as characteristic of epiphytic plants.

La sobrevivencia de las plantas epífitas a su ambiente depende de las adaptaciones vegetativas que les permiten afrontar diferentes tipos de estrés. Basado en la diversidad estructural de las Orchidaceae, el presente estudio tiene por objetivo relatar la estructura anatómica de Dichaea cogniauxiana y Epidendrum secundum con relación a los distintos ambientes donde viven. Hojas y raíces fueron recolectados en un bosque nuboso de un campo rupestre en la Serra da Piedade, Brasil. Dichaea cogniauxiana está adherida a los troncos, en sitios con alta humedad atmosférica y sombra, mientras que E. secundum está localizada en el margen del bosque nebular, en sitios más iluminados. Las hojas de E. secundum tienen una cutícula más gruesa y un mayor número de estomas por área que las de D. cogniauxiana, características coherentes con los diferentes patrones de exhibición a la luz del sol. Las cámaras supraestomáticas formadas por la cutícula pueden funcionar como una barrera de resistencia a la evaporación del agua. La suculencia de las hojas de E. secundum propicia el almacenamiento de ácidos orgánicos por la noche, y el almacenamiento de almidón puede estar implícito en el metabolismo de la PEP-carboxilasa. Las raíces con mayor velamen y especializadas paredes gruesas de las células corticales (ambas en E. secundum) ayudan a la absorción e indican una mejor adaptación al ambiente con intensa radiación solar y probable alto déficit de agua. El engrosamiento de la pared celular en la exodermis de E. secundum puede conferir una protección más eficaz contra el exceso de transpiración en el margen del bosque nebular. Por otra parte, D. cogniauxiana además de ser epífita, está en una posición baja, en un ambiente sombreado y con una alta humedad relativa. Su velamen delgado permite la entrada de la baja luz disponible y la fotosíntesis, produciendo oxígeno que ayuda a evitar la condición hipóxica.

Growth and photosynthetic performance of five tree seedlings species in response to natural light regimes from the Central Pacific of Costa Rica / Crecimiento y desempeño fotosintético de cinco plántulas de especies arbóreas en respuesta a regímenes lumínicos naturales del Pacífico Central de Costa Rica

Environmental heterogeneity mostly dominated by differing light regimes affects the expression of phenotypic plasticity, which is important for plant growth and survival, especially in the forest understory. The knowledge about these responses to this heterogeneity is a key factor for forest restoration initiatives. In this study, we determine several phenotypic responses to contrasting light conditions in five native tree seedling species of La Cangreja National Park, Central Pacific of Costa Rica, four of them with threatened or relict populations. After 14 weeks at a medium gap condition (24% of full sun), seedlings were transferred and acclimated for 11 weeks to three different natural light regimes: large gap (LG), medium gap (MG) and small gap (SG), corresponding to 52%, 24%, 9% of the mean direct and indirect radiation at each site from full sun. Growth, biomass allocation and leaf gas exchange were measured after the acclimation period. Four species strongly reduced relative growth rate (RGR) in the lower light condition. Total biomass (TB) and RGR were different in Hymenaea courbaril and Platymiscium curiense. H. courbaril and Astronium graveolens had significant changes in the maximum assimilation rate, with a mean value in the LG of 11.02 and 7.70µmolCO2/m²s, respectively. P. curuense showed the same trend and significant changes in RGR and biomass allocation. Aspidosperma myristicifolium and Plinia puriscalensis showed no adjustments to the light regimes in any of the measured variables. This study remarks the importance of determining the growth and physiological performance of these tree native species. It also demonstrates that the most threatened species are those with the less plastic responses to the light regimes, which stresses the difficult situation of their natural populations. This study highlights an urgent definition of the conservation and restoration needs of the degraded forests of the Costa Rican Central Pacific area, where these species dwell.

La heterogeneidad ambiental dominada mayormente por diferencias en los regímenes lumínicos afecta la expresión de la plasticidad fenotípica, la cual es importante para el crecimiento y la supervivencia de las plantas, especialmente en el sotobosque. Conocer dichas respuestas ante la heterogeneidad es un factor clave para las iniciativas de restauración forestal. En este estudio, determinamos varias respuestas fenotípicas ante condiciones lumínicas contrastantes de cinco especies de plántulas de árboles nativos del Pacífico Central de Costa Rica, algunos de ellos con poblaciones amenazadas. El crecimiento, la asignación de biomasa y el intercambio gaseoso a nivel foliar se midieron al final de once semanas de aclimatación en tres regímenes con diferente radiación: claro grande (LG), claro mediano (MG) y claro pequeño (SG) que corresponden al 54, 24 y 9% de la media del factor de radiación indirecta e indirecta en cada sitio a pleno sol, respectivamente. Cuatro especies presentan fuertes disminuciones en la tasa de crecimiento relativo (RGR) en la condición de poca luz. La biomasa total, RGR y la relación raíz/tallo fueron diferentes para todas las especies. Hymenaea courbaril y Astronium graveolens respondieron significativamente en la tasa de asimilación máxima, con un valor promedio en el LG de 11.02 y 7.70µmolCO2/m²s¹ respectivamente. Platymiscium curuense mostró tendencias similares y cambios significativos en la RGR y la asignación de biomasa. Aspidosperma myristicifolium y Plinia puriscalensis mostraron una plasticidad muy baja debido que no expresaron ajustes en ninguna de las variables medidas ante los regímenes de luz. Este estudio resalta la importancia de determinar el crecimiento y el rendimiento fisiológico de estas especies de árboles nativos. También demuestra que las especies más amenazadas son aquellas con las respuestas con menor plasticidad ante los regímenes luz, lo que acentúa la difícil situación de sus poblaciones naturales. Este estudio destaca una urgente definición de las necesidades de conservación y restauración de los bosques degradados de zona del Pacífico Central costarricense, donde estas especies habitan.

Photosynthesis of seedlings of Otoba novogranatensis (Myristicaceae) and Ruagea glabra (Meliaceae) in abandoned pasture, secondary forest and plantation habitats in Costa Rica / Fotosíntesis de plántulas de Otoba novogranatensis (Myristicaceae) y Ruagea glabra (Meliaceae) en pastizales abandonados, bosques secundarios y hábitats de plantaciones en Costa Rica

Enrichment planting in naturally recovering secondary forests or in tree plantations is increasingly being used as strategy to restore later-successional, large-seeded tropical forest trees. We seeded two tree species (Otoba novogranatensis and Ruagea glabra) in three agricultural sites in Southern Costa Rica: abandoned pastures, eight to ten year old secondary forests and three year old tree plantations (containing two N-fixing of four total tree species). We measured micrometeorological conditions, soil water content, plant water potential, leaf area, foliar C and N, and photosynthesis to better understand mechanistic responses of seedlings to conditions in the different successional habitats. Micrometeorological conditions, soil water content, and plant water potential were generally similar across habitats. Certain aspects of leaves (such as Specific Leaf Area and foliar N content), and photosynthesis (e.g. quantum yield and electron transport rate) were highest in the plantations, intermediate in the secondary forests, and lowest in abandoned pastures. Enhanced rates of photosynthetic biochemistry (such as Vcmax and Jmax) and Photosystem II efficiency (e.g. thermal energy dissipation) occurred in leaves from the plantations compared to the abandoned pastures, which may be related to higher leaf %N content. Results suggest that foliar N may be of greater importance than soil water content and micrometeorological factors in driving differences in photosynthetic processes across planting habitats. Planting seeds of these two species in plantations containing three year old trees (including two N-fixing species) enhances certain aspects of their photosynthesis and growth, compared to seedlings in abandoned pastures with non-native grasses, and thus can help increase forest recovery on abandoned agricultural lands.

El enriquecimiento de bosques secundarios o plantaciones forestales en proceso de regeneración natural por medio de la siembra de plántulas es una práctica cada vez más utilizada para restaurar bosques tropicales en estado de sucesión tardía. Sembramos dos especies de árboles (Otoba novogranatensis y Ruagea glabra) en pastizales abandonados, bosques secundarios de ocho a diez años de edad y plantaciones forestales de tres años de edad (con dos especies fijadoras de Nitrógeno de un total de cuatro especies) en tres sitios agrícolas en el Sur de Costa Rica. Medimos condiciones micrometeorológicas, contenido de agua del suelo, potencial hídrico de las plantas, área foliar, C y N foliar, y fotosíntesis para entender de una mejor manera las respuestas funcionales de las plántulas ante condiciones de distintos estadíos sucesionales. Las condiciones micrometeorológicas, contenido hídrico del suelo y el potencial hídrico de las plantas fueron mayoritariamente similares entre hábitats. Algunos aspectos de las hojas (como Área Foliar Específica y contenido de N foliar) y fotosíntesis (ej.: rendimiento cuántico y tasa de transporte de electrones) presentaron valores mayores en las plantaciones, intermedios en los bosques secundarios y menores en los pastizales abandonados. Se obtuvo un aumento en las tasas fotosintéticas bioquímicas (como Vcmax, Jmax) y la eficiencia del Fotosistema II (ej.: disipación de energía térmica) en hojas provenientes de las plantaciones comparado a las de los pastizales, posiblemente relacionado a un mayor %N foliar. Los resultados sugieren que el N foliar puede ser más importante que el contenido de agua del suelo y que los factores micrometeorológicos para marcar diferencias en los procesos fotosintéticos entre hábitats. Las plántulas de estas dos especies en las plantaciones con árboles de tres años de edad (incluyendo dos fijadoras de N) incrementaron ciertos aspectos de su fotosíntesis y crecimiento comparado a las plántulas en los pastizales abandonados de especies exóticas, por lo tanto, esta práctica puede ayudar a incrementar la recuperación de los bosques en áreas agrícolas abandonadas.

Variabilidad ambiental y respuestas fisiológicas de Polylepis cuadrijuga (Rosaceae) en un ambiente fragmentado en el Páramo de la Rusia (Colombia) / Environmental variability and physiological responses from Polylepis cuadrijuga (Rosaceae) in a fragmented environment in the Páramo de la Rusia (Colombia)

Polylepis cuadrijuga is an endemic woody species from the Colombian Eastern range, being the only tree species with capacity to live on mountainous environments beyond 4 000m of altitude. Grazing and agriculture have transformed at least 30% of the Guantiva-La Rusia region, turning continuous extensions of high Andean forest in a fragmented landscape, and P. cuadrijuga remnants have become smaller and more isolated. The aim of this study was to establish the environmental differences between a matrix of grazing pastures and the interior of fragments, to evaluate the physiological responses of P. cuadrijuga and determining the edge effect. Air temperature and humidity, soil water holding capacity and photosynthetic active radiation, were measured along two 50X2m transects from the matrix toward the center of fragment. Six trees inside the transects were chosen in each one of three sites (matrix, edge and interior) to measure the index chlorophyll content and to sample leaves to assess the leaf area, leaf biomass, specific leaf area, anatomy, health condition and pubescence. Results showed significantly differences between the matrix and the interior and intermediate conditions in the edge. Radiation, temperature and air desiccation were higher in the matrix than in the interior, submitting P. cuadrijuga trees to a stressing environment, where they presented stratification of epidermis and palisade parenchyma, and a higher leaf area, leaf thickness, chlorophyll content and pubescence than in the interior of fragments. All these physiological traits allow avoiding the photoxidation and damages by freezing or desiccation to which trees are exposed in a grazing pasture matrix. Nevertheless, there was a higher frequency of healthy leaves in the interior of fragments, showing that high irradiations and extreme air temperature and humidity reach adversely affect to P. cuadrijuga. Individuals in the edge had ecophysiological traits similar to the matrix ones, which confirm an edge effect that could penetrate 17m inside the fragments. We conclude that P. cuadrijuga is a plastic species, able to overcome the stress conditions from anthropogenic transformations, species able to be used in high Andean forest restoration programs.

Polylepis cuadrijuga es una especie leñosa endémica de la cordillera oriental de Colombia, donde la agricultura y el pastoreo han generado la fragmentación de sus bosques. Para determinar si existe un efecto borde en fragmentos ubicados en el Páramo de la Rusia, se establecieron diferencias ambientales y se evaluó las respuestas ecofisiológicas de P. cuadrijuga entre matriz de pastura, borde e interior de los fragmentos, a través de la medición de temperatura ambiental, humedad relativa, capacidad de retención de agua del suelo y radiación fotosintéticamente activa, a lo largo de dos transectos de 50m desde la matriz hacia el interior. En cada sitio se escogieron seis árboles para evaluar el contenido de clorofila, área foliar, biomasa foliar, área foliar específica, anatomía foliar, sanidad y pubescencia. En matriz fue mayor la temperatura y la radiación, condiciones relacionadas con la disminución del AFE y el aumento del contenido de clorofilas, evidenciado por la presencia de un parénquima en empalizada biestratificado. Características ecofisiológicas similares a las expuestas en borde, confirman un efecto de borde que podría penetra unos 17m en el interior de los fragmentos. Se concluye que P. cuadrijuga es una especie plástica, capaz de enfrentar condiciones de estrés generadas por actividades antropogénicas.