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Photosynthesis

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


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Journal ArticleDOI
TL;DR: Under controlled experimental conditions, the influences of light and temperature on the growth and metabolism of Egeria densa Planch, Hydrilla verticillata Royle, and Myriophyllum spicatum L. were comparatively examined.
Abstract: Under controlled experimental conditions, the influences of light and temperature on the growth and metabolism of Egeria densa Planch, Hydrilla verticillata Royle, and Myriophyllum spicatum L. were comparatively examined. Light was controlled at six levels ranging between 5 and 75% of full sunlight at solar noon. Water temperature was controlled at five levels ranging between 16? and 32?C. Growth considerations included morphology, biomass, and nutrition. Photosynthesis, respiration, and CO2 compensation points were determined to evaluate physiological differences in plant growth as affected by the experimental ranges of temperature and light. External morphology in these species was significantly affected by the different experimental light and temperature conditions. Both low light and high temperature promoted extensive shoot elongation and associated canopy formation. Biomass production and carbon metabolism in all species were influenced more by temperature than by light. Each of the species demonstrated metabolic acclimation to light over a broad range. Conversely, the macrophyte species considered here were not strictly capable of acclimating to temperature. Growth rate and the seasonal progression of senescence were interrelated in these species. Higher temperatures stimulated growth and promoted a compression of the growth cycle. The relationship between photosynthesis and respiration (P:R) was appreciably reduced by senescence, but the CO2 compensation point did not reflect this condition. In the species examined, CO2 compensation points decreased with increasing temperature, suggesting adaptations to low free CO2 levels in the environ- ment. Latitudinal differences in integral seasonal temperature, in relation to species-specific ranges of thermal tolerance, appear to be important in influencing the geographical distribution of the species considered here. Light may be the primary determinant of their depth distribution, but its importance in this regard could be somewhat diminished by their significant abilities to extend to the water surface under low light conditions.

353 citations

Journal ArticleDOI
TL;DR: The effects of starvation, glucose supplementation, and DCMU inhibition on the oxygen uptake rates in the light are described, and illumination was found to influence oxygen uptake by two mechanisms.

353 citations

Journal ArticleDOI
TL;DR: As the rate-limiting step in carbon assimilation, even modest improvements in the overall performance of Rubisco pose a viable pathway for obtaining significant gains in plant yield, particularly under stressful environmental conditions.
Abstract: Rubisco (ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase) enables net carbon fixation through the carboxylation of RuBP. However, some characteristics of Rubisco make it surprisingly inefficient and compromise photosynthetic productivity. For example, Rubisco catalyses a wasteful reaction with oxygen that leads to the release of previously fixed CO2 and NH3 and the consumption of energy during photorespiration. Furthermore, Rubisco is slow and large amounts are needed to support adequate photosynthetic rates. Consequently, Rubisco has been studied intensively as a prime target for manipulations to 'supercharge' photosynthesis and improve both productivity and resource use efficiency. The catalytic properties of Rubiscos from diverse sources vary considerably, suggesting that changes in turnover rate, affinity, or specificity for CO2 can be introduced to improve Rubisco performance in specific crops and environments. While attempts to manipulate plant Rubisco by nuclear transformation have had limited success, modifying its catalysis by targeted changes to its catalytic large subunit via chloroplast transformation have been much more successful. However, this technique is still in need of development for most major food crops including maize, wheat, and rice. Other bioengineering approaches for improving Rubisco performance include improving the activity of its ancillary protein, Rubisco activase, in addition to modulating the synthesis and degradation of Rubisco's inhibitory sugar phosphate ligands. As the rate-limiting step in carbon assimilation, even modest improvements in the overall performance of Rubisco pose a viable pathway for obtaining significant gains in plant yield, particularly under stressful environmental conditions.

353 citations

Journal ArticleDOI
TL;DR: Findings clearly indicates that salt stress did affect g s and g m but not the biochemical capacity to assimilate CO 2 and therefore, in these conditions, the sum of the diffusional resistances set the limit to photosynthesis rates.
Abstract: In this study it has been shown that increased diffusional resistances caused by salt stress may be fully overcome by exposing attached leaves to very low [CO 2 ] ( ~ ~ ~ 50 m mol mol - - 1 ), and, thus a non-destructive- in vivo method to correctly estimate photosynthetic capacity in stressed plants is reported. Diffusional (i.e. stomatal conductance, g s , and mesophyll conductance to CO 2 , g m ) and biochemical limitations to photosynthesis ( A ) were measured in two 1-yearold Greek olive cultivars (Chalkidikis and Kerkiras) subjected to salt stress by adding 200 m M NaCl to the irrigation water. Two sets of A ‐ C i curves were measured. A first set of standard A ‐ C i curves (i.e. without pre-conditioning plants at low [CO 2 ]), were generated for salt-stressed plants. A second set of A ‐ C i curves were measured, on both control and salt-stressed plants, after pre-conditioning leaves at [CO 2 ] of ~ 50 m mol mol - 1 for about 1.5 h to force stomatal opening. This forced stomata to be wide open, and g s increased to similar values in control and salt-stressed plants of both cultivars. After g s had approached the maximum value, the A ‐ C i response was again measured. The analysis of the photosynthetic capacity of the salt-stressed plants based on the standard A ‐ C i curves, showed low values of the J max (maximum rate of electron transport) to V cmax (RuBP-saturated rate of Rubisco) ratio (1.06), that would implicate a reduced rate of RuBP regeneration, and, thus, a metabolic impairment. However, the analysis of the A ‐ C i curves made on pre-conditioned leaves, showed that the estimates of the photosynthetic capacity parameters were much higher than in the standard A ‐ C i responses. Moreover, these values were similar in magnitude to the average values reported by Wullschleger ( Journal of Experimental Botany 44, 907‐920, 1993) in a survey of 109 C 3 species. These findings clearly indicates that: (1) salt stress did affect g s and g m but not the biochemical capacity to assimilate CO 2 and therefore, in these conditions, the sum of the diffusional resistances set the limit to photosynthesis rates; (2) there was a linear relationship ( r 2 = = = 0.68) between g m and g s , and, thus, changes of g m can be as fast as those of g s ; (3) the estimates of photosynthetic capacity based on A ‐ C i curves made without removing diffusional limitations are artificially low and lead to incorrect interpretations of the actual limitations of photosynthesis; and (4) the analysis of the photosynthetic properties in terms of stomatal and non-stomatal limitations should be replaced by the analysis of diffusional and non-diffusional limitations of photosynthesis. Finally, the C 3 photosynthesis model parameterization using in vitro -measured and in vivo measured kinetics parameters was compared. Applying the in vivo -measured Rubisco kinetics parameters resulted in a better parameterization of the photosynthesis model.

353 citations

Journal ArticleDOI
01 Jan 1995-Planta
TL;DR: It is concluded that a reversible modulation of gene expression in response to the export rate plays a central role in the mid-term feedback “sink” regulation of photosynthesis, and that feedback regulation of CO2 fixation by changes of Pi are of little importance in spinach under these conditions.
Abstract: Mature source leaves of spinach (Spinacia oleracea L.) plants growing hydroponically in a 9 h light (350 μmol photons·m−2 · s−1)/15 h dark cycle at 20° C in a climate chamber were fitted with a cold girdle around the petiole, 2 h into the light period. Samples were taken 1, 3 and 7 h later, and at the end of the photoperiod for the following 4 d. Control samples were taken from ungirdled leaves. In the first 7 h after fitting the cold girdle there was (compared to the control leaves) a two to five-fold accumulation of sucrose, glucose, fructose and starch, a 40–50% increase of hexose-phosphates and ribulose-1,5-bisphosphate, a decrease of glycerate-3-phosphate, a small decrease in sucrose-phosphate synthase activation, an increase of fructose-2,6-bisphosphate, increased activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), but no significant change in photosynthetic rate or stomatal conductance. Steady-state transcript levels for rbcS (small subunit of Rubisco) and atp-D (D-subunit of the thylakoid ATP synthase) decreased 30%, cab (chlorophyll-a-binding protein) decreased by 15% and agp-S (S-isoenzyme of ADP-glucose pyrophosphorylase) and nra (nitrate reductase) rose twofold. On the following days, levels of carbohydrates continued to rise and the changes of metabolites were maintained. Transcripts for rbcS, cab and atpD declined to 20, 70 and 25% of the control values. From day 3 onward the maximum activity of Rubisco declined. This was accompanied by a further increase of Rubisco activation to over 90% and, from day 4 onwards, an inhibition of photosynthesis which was associated with high internal CO2 concentration (ci), high ribulose-1,5-bisphosphate, and low glycerate-3-phosphate. When the cold-girdle was removed on day 5 there was a gradual recovery of photosynthesis and decline of ci over the next 2 d. Hexose-phosphates levels and transcripts for rbcS, cab and atp-D completely recovered within 2 d, even though the levels of carbohydrates had not fully recovered. Activity of Rubisco only reverted partly after 2 d, and Rubisco activation state and the ribulose-1,5-bisphosphate/glycerate-3-phosphate ratio were still higher than in control leaves. Transcripts for nra and agp-S were also still higher than in control leaves. It is concluded (i) that a reversible modulation of gene expression in response to the export rate plays a central role in the mid-term feedback “sink” regulation of photosynthesis, and (ii) that feedback regulation of CO2 fixation by changes of Pi are of little importance in spinach under these conditions. Further (iii) the rapid and reciprocal changes in nra and agpS transcripts, compared to rbcS, provide evidence that gene expression could also contribute to the modulation of nitrate assimilation and carbohydrate storage in conditions of decreased sink demand.

352 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20242
20232,453
20225,090
2021738
2020732
2019616