Effects of elevated CO(2) on chloroplast components, gas exchange and growth of oak and cherry.

Specific chloroplast proteins, gas exchange and dry matter production in oak (Quercus robur L.) seedlings and clonal cherry (Prunus avium L. x pseudocerasus Lind.) plants were measured during 19 months of growth in climate-controlled greenhouses at ambient (350 vpm) or elevated (700 vpm) CO(2). In both species, the elevated CO(2) treatment increased the PPFD saturated-rate of photosynthesis and dry matter production. After two months at elevated CO(2), Prunus plants showed significant increases in leaf (55%) and stem (61%) dry mass but not in root dry mass. However, this initial stimulation was not sustained: treatment differences in net assimilation rate (A) and plant dry mass were less after 10 months of growth than after 2 months of growth, suggesting acclimation of A to elevated CO(2) in Prunus. In contrast, after 10 months of growth at elevated CO(2), leaf dry mass of Quercus increased (130%) along with shoot (356%) and root (219%) dry mass, and A was also twice that of plants grown and measured at ambient CO(2). The amounts of Rubisco and the thylakoid-bound protein cytochrome f were higher in Quercus plants grown for 19 months in elevated CO(2) than in control plants, whereas in Prunus there was less Rubisco in plants grown for 19 months in elevated CO(2) than in control plants. Exposure to elevated CO(2) for 10 months resulted in increased mean leaf area in both species and increased abaxial stomatal density in Quercus. There was no change in leaf epidermal cell size in either species in response to the elevated CO(2) treatment. The lack of acclimation of photosynthesis in oak grown at elevated CO(2) is discussed in relation to the production and allocation of dry matter. We propose that differences in carbohydrate utilization underlie the differing long-term CO(2) responses of the two species.

Inducible overexpression of oat arginine decarboxylase in transgenic tobacco plants.

To test the possible interaction of polyamines in plant growth responses, transgenic tobacco plants containing the Avena sativa L. (oat) arginine decarboxylase (ADC) gene under the control of a tetracycline-inducible promoter were generated. Inducible overexpression of oat ADC in transgenic tobacco led to an accumulation of ADC mRNA, increased ADC activity and changes in polyamine levels. Transgenic lines, induced during vegetative stage, displayed different degrees of an altered phenotype, the severity of which was correlated with putrescine content. These phenotypic changes were characterized by short internodes, thin stems and leaves, leaf chlorosis and necrosis, as well as reduced root growth. This is the first report to show altered phenotypes as a consequence of polyamine changes under tetracycline-induction in in vivo conditions. Interestingly, overexpression of oat ADC in tobacco resulted in similar detrimental effects to those observed by ADC activation induced by osmotic stress in the homologous oat leaf system. In the context of the role of specific polyamines in plant growth and development, the present results indicate that activation of the ADC pathway leading to high levels of endogenous putrescine (or its catabolytes) is toxic for the vegetative growth of the plant. In contrast, no visible phenotypic effects were observed in flowering plants following tetracycline induction. Further characterization of the different transgenic lines may shed light on the action of specific polyamines in different plant developmental processes.

Photoperiod effect on bud burst in Prunus is phase dependent: significance for early photosynthetic development.

A 16-h photoperiod stimulated bud burst in mature rooted cuttings of Prunus avium cv. Stella, but not in selfed Stella seedlings. However, in a 12-h photoperiod, bud burst occurred earlier in the seedlings than in the mature cuttings. In the 12-h photoperiod, production of polypeptides involved in carbon dioxide fixation and photosynthetic electron transport was higher in seedlings than in mature cuttings, whereas in the 16-h photoperiod, shoot development and polypeptide production were similar in seedlings and mature cuttings. In both photoperiods, the amount of large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase that was associated with thylakoid membranes in young leaves was higher in seedlings than in mature cuttings. Transcript levels of rbcL mRNA were influenced by photoperiod in mature cuttings but not in seedlings. In seedlings, early bud burst and development of the light harvesting apparatus would be an advantage at the start of the growing season, before the mature tree canopy reduces irradiances near the woodland floor.

Acclimation of photosynthesis to elevated CO2 through feedback regulation of gene expression: Climate of opinion.

Although down-regulation of photosynthesis in higher C3 plants exposed to long-term elevated CO2 has been recognized in plants with low sink activity or poor nutrient status, the underlying molecular mechanisms remain unclear. This review covers aspects of rising CO2 on plant productivity in general, and then focuses on photosynthesis, biochemistry (stroma and thylakoid proteins, Rubisco activities and metabolites), and gene expression in tomato plants grown under ambient or elevated CO2. Taking into account these data and the recent discovery that glucose triggers repression of photosynthetic gene transcription, a molecular mechanism is proposed for feedback regulation of photosynthesis under high CO2. Different living organisms such as bacteria, yeast, and mammals have been investigated for the sensing mechanisms of the carbohydrate status of their cells, and this information is used together with some recent data obtained for plants to propose how hexose levels might be sensed in higher plant cells.

Arginine Decarboxylase Is Localized in Chloroplasts.

Plants, unlike animals, can use either ornithine decarboxylase or arginine decarboxylase (ADC) to produce the polyamine precursor putrescine. Lack of knowledge of the exact cellular and subcellular location of these enzymes has been one of the main obstacles to our understanding of the biological role of polyamines in plants. We have generated polyclonal antibodies to oat (Avena sativa L.) ADC to study the spatial distribution and subcellular localization of ADC protein in different oat tissues. By immunoblotting and immunocytochemistry, we show that ADC is organ specific. By cell fractionation and immunoblotting, we show that ADC is localized in chloroplasts associated with the thylakoid membrane. The results also show that increased levels of ADC protein are correlated with high levels of ADC activity and putrescine in osmotically stressed oat leaves. A model of compartmentalization for the arginine pathway and putrescine biosynthesis in active photosynthetic tissues has been proposed. In the context of endosymbiote-driven metabolic evolution in plants, the location of ADC in the chloroplast compartment may have major evolutionary significance, since it explains (a) why plants can use two alternative pathways for putrescine biosynthesis and (b) why animals do not possess ADC.

Effects of elevated CO(2) on growth and chloroplast proteins in Prunus avium.

To predict the future carbon sequestering capacity of trees, we need information about the possible acclimatory mechanisms of plant growth and photosynthesis in rising atmospheric CO(2) under a variety of environmental conditions. We have, therefore, studied the growth response of a tree species (Prunus avium L. Stella (wild cherry)) to elevated CO(2) and characterized the associated changes in photosynthetic machinery of the leaf tissue. Self-pollinated seedlings and mature cuttings (clones) from the same parent plant of P. avium were grown for two consecutive growing seasons (about 60 days each) in ambient CO(2) (350 micro mol mol(-1) CO(2)) or elevated CO(2) (700 micro mol mol(-1) CO(2)) with a high or low nutrient supply. The degree of acclimation of leaf biochemistry and growth response to elevated CO(2) was dependent on the plant material (seedling or mature cutting) and nutrient supply. There was little or no growth response to elevated CO(2) in seedlings or cuttings in the low nutrient supply treatments, whereas, in both seasons, there was a strongly positive growth response to elevated CO(2) in seedlings and cuttings in the high nutrient supply regimes, resulting in increases in the root/shoot ratio and in carbon allocation to the roots. In contrast, the protein content and activity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco, EC 4.1.1.39) were down regulated in elevated CO(2). The loss of Rubisco on an area basis in plants in the elevated CO(2) treatments was compensated for at the canopy level by increased leaf area. The loss of Rubisco protein was accompanied by decreases in the contents of chlorophyll and the thylakoid membrane proteins D(1), D(2) and cytochrome f, which are involved in light harvesting and photo-electron transport. We conclude that, in the medium- to long-term, the initial stimulation of biomass production by elevated CO(2) may be increasingly offset by a lower photosynthetic capacity per unit leaf area in perennial plants.

Rubisco and PEP carboxylase responses to changing irradiance in a Brazilian Cerrado tree species, Qualea grandiflora Mart. (Vochysiaceae).

The activities of ribulose-1,5-bisphosphate carboxylase-oxygenase, Rubisco (E.C. 4.1.1.39) and phosphoenolpyruvate carboxylase, PEPc (E.C. 4.1.1.31), and concentrations of protein and chlorophyll were measured in extracts from cotyledons and first leaves of Qualea grandiflora Mart. (Vochysiaceae) seedlings after transfer from high-light (20 days at 320 micro mol m(-2) s(-1), PAR) to low-light (35 days at 120 micro mol m(-2) s(-1), PAR) conditions. When Tween 20 and glycerol were added to the extraction medium, Rubisco activities obtained for Qualea grandiflora were comparable to published values for several coniferous species and the broad-leaved species, Prunus avium L. Stella, grown in a similar light environment. Rubisco activity in cotyledons of Q. grandiflora grown in high light for 20 days and then transferred to low light for a further 35 days was similar to the activity in cotyledons of plants grown continuously in high light. However, the first leaf above the cotyledons showed a greater response to the change in irradiance; in high light, Rubisco activity of the first leaf was 1.8 times higher on a fresh weight basis and 2.7 times higher on an area basis than that of leaves transferred from high to low light. Fresh weight and chlorophyll concentration expressed on a unit leaf area basis were also higher in the high-light treatment. These responses to irradiance are indicative of a species adapted to growth in an unshaded habitat. The PEPc activity in leaves was 15% of Rubisco activity, which is typical of species with a C(3) photosynthetic pathway. The relatively slow growth rate of Q. grandiflora observed in these experiments could not be attributed to a low carboxylation capacity per unit leaf area.

Characterization of conformers of D 1 of photosystem II using site-directed antibodies.

Antibodies have been raised to synthetic peptides, corresponding to a region in the loop spanning helices 4 and 5 of D 1 protein (Ala 250-Phe 265) and to a region anticipated to be near the C terminus of mature D 1 (His 332-Ala 345). Polyclonal antibodies to the sequence His 332-Ala 345 reacted with a 32 kDa polypeptide in thylakoid preparations identified as D 1 from its resistance (pea) or susceptibility (wheat) to lysine-C degradation. A monoclonal antibody to His 332-Ala 345 reacted preferentially with a faster migrating polypeptide in SDS electrophoresis, a putative conformer of D 1. Polyclonal antibodies to the sequence Ala 250-Phe 265 also reacted with the faster running polypeptide but not with the population of molecules running at 32 kDa. The putative conformer of D 1 from wheat appears to be more resistant than the main D 1 population to lysine-C degradation. Peptide analyses by Takahashi et al. [(1988) FEBS Lett, 240, 6-8] suggest Asn 335-Ala 344 lies at the processed C terminus. The present report provides immunological confirmation that this sequence is retained in mature D 1.