Gabaculine alters plastid development and differentially affects abundance of plastid-encoded DPOR and nuclear-encoded GluTR and FLU-like proteins in spruce cotyledons.

Synthesis of 5-aminolevulinic acid (ALA) represents a rate limiting step in the tetrapyrrole biosynthetic pathway, and is regulated by metabolic feedback control of glutamyl-tRNA reductase (GluTR) activity. The FLU protein has been attributed to this regulation. Later in the biosynthetic pathway, reduction of protochlorophyllide (Pchlide), catalyzed by protochlorophyllide oxidoreductase (POR), ensures another important regulatory step in the chlorophyll biosynthesis. In the present work, we investigated the expression and cellular abundance of nuclear-encoded and plastid-encoded proteins involved in ALA synthesis and Pchlide reduction in Norway spruce (Picea abies L. Karst.) as a representative of plant species with high ability to synthesize chlorophyll in the dark. Using dark-grown, light/dark-grown and gabaculine-treated seedlings, we demonstrated that gabaculine-impaired etiochloroplast and chloroplast development has no negative effect on GluTR accumulation in the cotyledons. However, in contrast to control plants, the relative amount of GluTR was similar both in the dark-grown and light/dark-grown gabaculine-treated seedlings. We identified a partial sequence of the FLU-like gene in Norway spruce, and using antibodies against the FLU-like protein (FLP), we showed that FLP accumulated mostly in the dark-grown control seedlings and gabaculine-treated seedlings. In contrast to nuclear-encoded GluTR and FLP, accumulation of plastid-encoded light-independent POR (DPOR) was sensitive to gabaculine treatment. The levels of DPOR subunits were substantially lower in the light/dark-grown control seedlings and gabaculine-treated seedlings, although the corresponding genes chlL, chlN and chlB were expressed. Since we analyzed the samples with different plastid types, plastid ultrastructure and physiological parameters like Pchlide and chlorophyll contents, in vivo chlorophyll fluorescence and photosynthetic efficiency of the seedlings were characterized. Apart from etiochloroplast-specific accumulation of the DPOR subunits, we described, in some detail, additional specific features of chlorophyll biosynthesis in the spruce seedlings that differ from those known in angiosperms.

Trap closure and prey retention in Venus flytrap (Dionaea muscipula) temporarily reduces photosynthesis and stimulates respiration.

BACKGROUND AND AIMS: The carnivorous plant Venus flytrap (Dionaea muscipula) produces a rosette of leaves: each leaf is divided into a lower part called the lamina and an upper part, the trap, with sensory trigger hairs on the adaxial surface. The trap catches prey by very rapid closure, within a fraction of a second of the trigger hairs being touched twice. Generation of action potentials plays an important role in closure. Because electrical signals are involved in reduction of the photosynthetic rate in different plant species, we hypothesized that trap closure and subsequent movement of prey in the trap will result in transient downregulation of photosynthesis, thus representing the energetic costs of carnivory associated with an active trapping mechanism, which has not been previously described. METHODS: Traps were enclosed in a gas exchange cuvette and the trigger hairs irritated with thin wire, thus simulating insect capture and retention. Respiration rate was measured in darkness (RD). In the light, net photosynthetic rate (AN), stomatal conductance (gs) and intercellular CO2 concentration (ci) were measured, combined with chlorophyll fluorescence imaging. Responses were monitored in the lamina and trap separately. KEY RESULTS: Irritation of trigger hairs resulted in decreased AN and increased RD, not only immediately after trap closure but also during the subsequent period when prey retention was simulated in the closed trap. Stomatal conductance remained stable, indicating no stomatal limitation of AN, so ci increased. At the same time, the effective quantum yield of photosystem II (PSII) decreased transiently. The response was confined mainly to the digestive zone of the trap and was not observed in the lamina. Stopping mechanical irritation resulted in recovery of AN, RD and PSII. CONCLUSIONS: We put forward the first experimental evidence for energetic demands and carbon costs during insect trapping and retention in carnivorous plants, providing a new insight into the cost/benefit model of carnivory.

A novel insight into the regulation of light-independent chlorophyll biosynthesis in Larix decidua and Picea abies seedlings.

Light-independent chlorophyll (Chl) biosynthesis is a prerequisite for the assembly of photosynthetic pigment-protein complexes in the dark. Dark-grown Larix decidua Mill. seedlings synthesize Chl only in the early developmental stages and their Chl level rapidly declines during the subsequent development. Our analysis of the key regulatory steps in Chl biosynthesis revealed that etiolation of initially green dark-grown larch cotyledons is connected with decreasing content of glutamyl-tRNA reductase and reduced 5-aminolevulinic acid synthesizing capacity. The level of the Chl precursor protochlorophyllide also declined in the developing larch cotyledons. Although the genes chlL, chlN and chlB encoding subunits of the light-independent protochlorophyllide oxidoreductase were constitutively expressed in the larch seedlings, the accumulation of the ChlB subunit was developmentally regulated and ChlB content decreased in the fully developed cotyledons. The efficiency of chlB RNA-editing was also reduced in the mature dark-grown larch seedlings. In contrast to larch, dark-grown seedlings of Picea abies (L.) Karst. accumulate Chl throughout their whole development and show a different control of ChlB expression. Analysis of the plastid ultrastructure, photosynthetic proteins by Western blotting and photosynthetic parameters by gas exchange and Chl fluorescence measurements provide additional experimental proofs for differences between dark and light Chl biosynthesis in spruce and larch seedlings.

Feeding enhances photosynthetic efficiency in the carnivorous pitcher plant Nepenthes talangensis.

BACKGROUND AND AIMS: Cost-benefit models predict that carnivory can increase the rate of photosynthesis (A(N)) by leaves of carnivorous plants as a result of increased nitrogen absorption from prey. However, the cost of carnivory includes decreased A(N) and increased respiration rates (R(D)) of trapping organs. The principal aim of the present study was to assess the costs and benefits of carnivory in the pitcher plant Nepenthes talangensis, leaves of which are composed of a lamina and a pitcher trap, in response to feeding with beetle larvae. METHODS: Pitchers of Nepenthes grown at 200 micromol m(-2) s(-1) photosynthetically active radiation (PAR) were fed with insect larvae for 2 months, and the effects on the photosynthetic processes were then assessed by simultaneous measurements of gas exchange and chlorophyll fluorescence of laminae and pitchers, which were correlated with nitrogen, carbon and total chlorophyll concentrations. KEY RESULTS: A(N) and maximum (F(v)/F(m)) and effective quantum yield of photosystem II (Phi(PSII)) were greater in the fed than unfed laminae but not in the fed compared with unfed pitchers. Respiration rate was not significantly affected in fed compared with unfed plants. The unfed plants had greater non-photochemical quenching (NPQ) of chlorophyll fluorescence. Higher NPQ in unfed lamina did not compensate for their lower Phi(PSII), resulting in lower photochemical quenching (QP) and thus higher excitation pressure on PSII. Biomass and nitrogen and chlorophyll concentration also increased as a result of feeding. The cost of carnivory was shown by lower A(N) and Phi(PSII) in pitchers than in laminae, but R(D) depended on whether it was expressed on a dry weight or a surface area basis. Correlation between nitrogen and A(N) in the pitchers was not found. Cost-benefit analysis showed a large beneficial effect on photosynthesis from feeding as light intensity increased from 200 to 1000 micromol m(-2) s(-1) PAR after which it did not increase further. All fed plants began to flower. CONCLUSION: Feeding pitchers with insect larvae increases A(N) of leaf laminae, due to higher nutrient acquisition, with strong correlation with nitrogen concentration, but A(N) of pitchers does not increase, despite increased nitrogen concentration in their tissue. Increased A(N) improves growth and reproduction and is likely to increase the competitive advantage of carnivorous over non-carnivorous plants in nutrient-poor habitats.

Carnivorous syndrome in Asian pitcher plants of the genus Nepenthes.

BACKGROUND AND AIMS: Pitcher plants Nepenthes alata and N. mirabilis are carnivorous species with leaves composed of a photosynthetic part (lamina) and a pitcher trap. This characteristic permitted direct physiological and anatomical comparison between these two distinct parts of the leaves to determine those features involved in the 'carnivorous syndrome', which include low net photosynthetic assimilation rate (A(N)) and low photosynthetic nitrogen use efficiency (PNUE). METHODS: Photosynthetic rate (A(N)) and respiration rate (R(d)) were measured gasometrically, chlorophyll concentration was determined spectrophotometrically and nitrogen concentration was determined using a CHN elemental analyser in lamina and trap separately. Anatomy of N. alata was observed using light, fluorescence and transmission electron microscopy. A(N), foliar nitrogen and chlorophyll concentration were also compared with values for other carnivorous plant species (genera Sarracenia, Drosera) that combine both autotrophic and carnivorous functions into the same physical organ. KEY RESULTS: It was found that the A(N) in Nepenthes lamina was low and PNUE was only slightly higher or similar in comparison with other carnivorous plants. It was not observed that the pitcher had a higher R(d) than the lamina, but A(N) in the pitcher was significantly lower than in the lamina. Nepenthes possesses a cluster of characters that could result in reduced photosynthesis in the pitcher and be responsible for carnivorous function of the leaf: replacement of chlorophyll-containing cells with digestive glands, low chlorophyll and nitrogen concentration, compact mesophyll with a small portion of intercellular spaces, absence of palisade parenchyma and low stomatal density. CONCLUSION: Low photosynthetic capacity, nitrogen efficiency, chlorophyll and nitrogen concentration of Nepenthes pitchers was found, together with a set of features that characterized the carnivorous syndrome. Dual use of leaves for photosynthesis and nutrient gain can decrease photosynthetic efficiency in carnivorous plants in general.

Plastid structure and chlorophyll content in leaf primordia of onion bulbs.

Angiosperms do not synthesize chlorophyll in the dark. Here we show that leaf primordia in onion bulbs are green, though they developing in dark conditions. We present results that show plastids in green primordia are chloroplasts, and that they contain chlorophyll as well as embryos in seeds of certain angiosperms.