Photosynthesis

About: Photosynthesis is a research topic. Over the lifetime, 19789 publications have been published within this topic receiving 895197 citations.

Chlorophyll biosynthesis in bacteria: the origins of structural and functional diversity.

Abstract: The use of photochemical reaction centers to convert light energy into chemical energy, chlorophototrophy, occurs in organisms belonging to only five eubacterial phyla: Cyanobacteria, Proteobacteria, Chlorobi, Chloroflexi, and Firmicutes. All chlorophototrophs synthesize two types of pigments: (a) chlorophylls and bacteriochlorophylls, which function in both light harvesting and uniquely in photochemistry; and (b) carotenoids, which function primarily as photoprotective pigments but can also participate in light harvesting. Although hundreds of carotenoids have been identified, only 12 types of chlorophylls (Chl a, b, d; divinyl-Chl a and b; and 8(1)-hydroxy-Chl a) and bacteriochlorophylls (BChl a, b, c, d, e, and g) are currently known to occur in bacteria. This review summarizes recent progress in the identification of genes and enzymes in the biosynthetic pathways leading to Chls and BChls, the essential tetrapyrrole cofactors of photosynthesis, and addresses the mechanisms for generating functional diversity for solar energy capture and conversion in chlorophototrophs.

Photosynthesis in Salt-Stressed Grapevines

Abstract: Rooted cuttings of grapevine (Vitis vinifera L. cv. Sultana syn. Thompson Seedless) were grown in sand culture irrigated with nutrient solution containing 1-125 mM NaCl. The effect of salinity on vine growth and photosynthesis is described. Salinity led to reduced growth where foliar symptoms of salt toxicity were absent. Rates of CO2 fixation decreased with increasing levels of chloride in leaves. This decrease in photosynthesis could be largely attributed to increased residual (mesophyll) resistance to CO2 fixation. Radiotracer studies showed that salt stress led to the accumulation of label in intermediates of the glycollate pathway. Salt-stressed leaves contained decreased amounts of sucrose and starch, but increased levels of reducing sugars.

Effects of light quality on CO2 assimilation, chlorophyll-fluorescence quenching, expression of Calvin cycle genes and carbohydrate accumulation in Cucumis sativus.

Abstract: Light quality is thought to affect many plant physiological processes during growth and development, particularly photosynthesis. We examined how light quality influences plant photosynthesis by analyzing changes in photosynthetic parameters and expression levels of some photosynthesis related genes of cucumber (Cucumis sativus L. cv. Jinyou No. 1) plants. The plants were grown under different light qualities: purple (P), blue (B), green (G), yellow (Y), red (R) and white light (W) of the same photosynthetic photon flux density (PFD) about 350 micromol m(-2)s(-1) for 5 days. The results show that all plants grown under monochromatic light had reduced growth, CO(2) assimilation rate (Pn) and quantum yield of PSII electron transport (Phi(PSII)) as compared with plants grown under W, and these reductions were more significant in the plants under G, Y and R. The decrease in Phi(PSII) is mostly due to the reduction in photochemical quenching (qP). Interestingly, P- and B-grown plants had higher stomatal conductance (Gs), total and initial Rubisco activities and higher transcriptional levels of 10 genes which encode key enzymes in the Calvin cycle together with higher total soluble sugars, sucrose and starch contents as compared with W-grown plants, whereas in G-, Y-, and R-grown plants these parameters declined. Therefore, the reduction in Pn under P and B is likely the result of inactivation of photosystems, whilst under Y, G and R it is caused by, in addition to photosystem inactivation, the closure of stomata and the transcriptional down-regulation of genes for the Calvin cycle enzymes such as rbc L and rca. In conclusion, light quality alters plant photosynthesis by the effects on the activity of photosynthetic apparatus in leaves and the effects on the expression and/or activity of the Calvin cycle enzymes.

Up-regulation of the mitochondrial alternative oxidase pathway enhances photosynthetic electron transport under drought conditions

Abstract: The aim of this study was to explore the role of the mitochondrial alternative oxidase (AOX) in the protection of photosynthesis during drought in wheat leaves. The relative water contents of water-replete and drought-exposed wheat plants were 97.2+/-0.3 and 75+/-2, respectively. Drought increased the amount of leaf AOX protein and also enhanced the rate of AOX-dependent O(2) uptake by the respiratory electron transport chain. The amount of the reduced, active form of the AOX protein was specifically increased by drought. The AOX inhibitor salicylhydroxamic acid (1 mM; SHAM) inhibited 70% of AOX activity in vivo in both water-replete and drought-exposed plants. Plants treated with SHAM were then exposed to low (100), high (350), or excess light (800 mumol photons m(-2) s(-1)) for 90 min. SHAM did not modify chlorophyll a fluorescence quenching parameters in water-replete controls after any of these treatments. However, while the maximal quantum yield of photosystem II (PSII) electron transport (F(v)/F(m)) was not affected by SHAM, the immediate quantum yield of PSII electron transport (Phi(PSII)) and photochemical quenching (qP) were gradually reduced by increasing irradiance in SHAM-treated drought-exposed plants, the decrease being most pronounced at the highest irradiance. Non-photochemical quenching (NPQ) reached near maximum levels in plants subjected to drought at high irradiance. However, a combination of drought and low light caused an intermediate increase in NPQ, which attained higher values when AOX was inhibited. Taken together, these results show that up-regulation of the respiratory AOX pathway protects the photosynthetic electron transport chain from the harmful effects of excess light.