Photosynthesis

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

The growth of soybean under free air [CO2] enrichment (FACE) stimulates photosynthesis while decreasing in vivo Rubisco capacity

Abstract: Down-regulation of light-saturated photosyn- thesis (Asat) at elevated atmospheric CO2 concentration, (CO2), has been demonstrated for many C3 species and is often associated with inability to utilize additional photosynthate and/or nitrogen limitation. In soybean, a nitrogen-fixing species, both limitations are less likely than in crops lacking an N-fixing symbiont. Prior studies have used controlled environment or field enclosures where the artificial environment can modify responses to (CO2). A soybean free air (CO2) enrichment (FACE) facility has provided the first opportunity to analyze the effects of elevated (CO2) on photosynthesis under fully open-air conditions. Potential ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation (Vc,max) and electron transport through photosystem II (Jmax) were determined from the responses of Asat to intercel- lular (CO2 )( Ci) throughout two growing seasons. Mesophyll conductance to CO2 (gm) was determined from the responses of Asat and whole chain electron transport (J) to light. Elevated (CO2) increased Asat by 15-20% even though there was a small, statistically significant, decrease in Vc,max. This differs from previous studies in that Vc,max/Jmax decreased, inferring a shift in resource investment away from Rubisco. This raised the Ci at which the transition from Rubisco-limited to ribulose-1,5-bisphosphate regeneration-limited photosynthesis occurred. The decrease in Vc,max was not the result of a change in gm, which was unchanged by elevated (CO2). This first analysis of limitations to soy- bean photosynthesis under fully open-air conditions re- veals important differences to prior studies that have used enclosures to elevate (CO2), most significantly a smaller response of Asat and an apparent shift in re- sources away from Rubisco relative to capacity for electron transport.

Photoacclimation in the marine diatom Skeletonema costatum

Abstract: Photoacclimation was examined in the marine diatom Skeletonema costatum, which was subjected to reciprocal shifts between irradiances of 50 (low-light) and 1,200 (high-light) mmol photons m 22 s 21 . Cell chlorophyll a and fucoxanthin contents were higher but diadinoxanthin and diatoxanthin contents lower in cells grown at 50 mmol photons m 22 s 21 than in cells shifted to 1200 mmol photons m 22 s 21 . Cell carbon contents measured at the start of the light period were similar in both high-light and low-light treatments. However, b y 6 h into the light period, the carbon contents in the high-light cells were about twofold higher than in the low-light cells. Dark respiration rates, dark Chl a synthesis rates, and dark cell-division rates were greater in the high-light acclimated cells than in the low-light cells. Thus, there was a greater uncoupling of carbon assimilation from cell division during the day in the high-light cells, but pigment synthesis and cell division continued in darkness. Cell-specific, light saturated photosynthesis rates, and chlorophyll a specific light-limited photosynthesis rates were constant during reciprocal shifts between growth irradiances of 50 and 1200 mmol photons m 22 s 21 . Thus, differences of photosynthesis versus irradiance curves between cells acclimated to high-light versus low-light could be accounted for largely in terms of changes in cell chlorophyll a contents. Although the chlorophyll a-specific initial slope, a chl , was constant, the chlorophyll a-specific light absorbtion coeffecient, a chl , increased and the maximum quantum efficiency of photosynthesis (fm) declined following the shift to high light. The increase of a chl was most likely due to a decreased package effect. The decline of fm was most likely due to accumulation of xanthophyll cycle pigments. Carbonspecific, light-saturated photosynthesis rates were lower in high-light than in low-light cells; this observation may indicate that control of light-saturated photosynthesis shifts from enzymes of the carbon dioxide reduction cycle (Calvin cycle) in low-light cells to the photosynthetic electron transfer chain in high-light cells.

Internal Leaf Area and Cellular CO2 Resistance: Photosynthetic Implications of Variations with Growth Conditions and Plant Species

Abstract: The influences of illumination, temperature, and soil water potential during development on leaf thickness, mesophyll cell wall area per unit leaf area (Ames/A), and the cellular CO2, resistance expressed on a mesophyll cell wall area basis (rCO2cell,) were examined for Plectranthus parviflorus Henckel. Although the ranges of all three growth conditions caused at least 9-fold variations in the leaf biomass produced in 4 weeks, only the illumination had a major effect on internal leaf morphology, e.g. the thickness went from 279 to 831 μm and Ames/A from 10.5 to 34.8 as the photosynthetically active radiation was raised from 3 to 53 nEinsteins cm−2 s−1, while rCO2cell remained close to 154 s cm−1. Variations in the growth temperature, soil water potential, and the nutritional status of the plant, affected photosynthesis mainly by changes in rCO2cell. To compare the influence of internal leaf area on photosynthesis for other plants, especially those with low Ames/A values, the maximum rates of CO2 uptake at light saturation and photosynthetically optimal temperatures were also determined for a moss, Mnium ciliare (C. Muell.) Schimp., and two ferns, Adiantum decorum Moore and Alsophila australe R. Br. As Ames/A went from 2.00 for the moss to 3.8, 7.5, 11.7, and 20.8 for the fens, the illumination at light saturation and the maximum rate of photosynthesis both progressively increased. The cellular CO2 resistance, which theoretically might have a lower limit of 20 s cm−1, ranged from 85 to 190 s cm−1.

High-resolution two-dimensional electrophoresis separation of proteins from metal-stressed rice (Oryza sativa L.) leaves: drastic reductions/fragmentation of ribulose-1,5-bisphosphate carboxylase/oxygenase and induction of stress-related proteins.

Abstract: Employing high-resolution two-dimensional electrophoresis (2-DE), we studied changes in the rice leaf protein patterns, in response to applied heavy and alkaline metals, important environmental pollutants in our surroundings. Drastic changes in 2-DE protein patterns after treatment with copper, cadmium, and mercury, over control were found, including changes in the morphology of the leaf segments. Changes in the major leaf photosynthetic protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO, both suppression and fragmentation), and induction of proteins are reported. A total of 33 proteins, which were highly reproducible in repeated experiments, were visually identified as changed over the control, and taken for N-terminal or internal amino acid sequencing. Among these, nine proteins were N-terminally blocked, and six proteins could not be sequenced. Most of the proteins showed homology to RuBisCO protein, and some to defense/stress-related proteins, like the pathogenesis related class 5 protein (OsPR5), the probenazole-inducible protein (referred to as the OsPR10), superoxide dismutase, and the oxygen evolving protein. Results presented here strongly indicate a highly specific action of some of these metals in disturbing the photosynthetic machinery, as evidenced by prominent reductions/fragmentation of the major photosynthetic protein, RuBisCO, and resulting in stress.