Net photosynthetic rate (PN) in the mother leaves was higher in the drought tolerant (DT) clones of tea (Camellia sinensis) while liberation of the fixed 14C in light from the mother leaves was higher in the drought susceptible (DS) clones. The DT clones translocated more photosynthates to the crop shoots (three leaves and a bud) from the mother leaf than the DS clones. Concentrations of RuBP carboxylase (RuBPC) or oxygenase (RuBPO) had no relationship with the drought tolerant nature of tea clones but their ratio correlated with the same. DT tea clones had higher catalase activity that could scavenge the hydrogen peroxide formed in the photorespiratory pathway and thereby reduced photorespiration rate (PR). The ratio of RuBPC/RuBPO had a positive correlation with PN and catalase activity. Negative correlation between RuBPC/RuBPO and PR and between catalase activity and RuBPO activity was established. and P. R. Jeyaramraja ... [et al.].
In the course of dehydration, the gas exchange and chlorophyll (Chl) fluorescence were measured under irradiance of 800 μmol m-2 s-1 in detached apple leaves, and the production of active oxygen species (AOS), hydrogen peroxide (H2O2), superoxide (O2-), hydroxyl radical (-OH), and singlet oxygen (1O2), were determined. Leaf net photosynthetic rate (PN) was limited by stomatal and non-stomatal factors at slight (2-3 h dehydration) and moderate (4-5 h dehydration) water deficiency, respectively. Photoinhibition occurred after 3-h dehydration, which was defined by the decrease of photosystem 2 (PS2) non-cyclic electron transport (P-rate). After 2-h dehydration, an obvious rise in H2O2 production was found as a result of photorespiration rise. If photorespiration was inhibited by sodium bisulfite (NaHSO3), the rate of post-irradiation transient increase in Chl fluorescence (Rfp) was enhanced in parallel with a slight decline in P-rate and with an increase in Mehler reaction. At 3-h dehydration, leaf P-rate decrease could be blocked by glycine (Gly) or methyl viologen (MV) pre-treatment, and MV was more effective than Gly at moderate drought time. AOS (H2O2 and O2-), prior to photoinhibition produced from photorespiration and Mehler reaction in detached apple leaves at slight water deficiency, were important in dissipating photon energy which was excess to the demand of CO2 assimilation. So photoinhibition could be effectively prevented by the way of AOS production. and H. S. Jia, Y. Q. Han, D. Q. Li.
In order to investigate the photoprotective function of photorespiration in grapevine under water stress, potted grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) were randomly divided into three uniform groups for well-watered [watered every morning to keep the relative water content (RWC) of soil over 70 %], water-stress adapted (drought-adapted at 30 % relative soil water content for 30 days), and water stress without adaptation treatment (water-stressed to 30 % relative soil water content for 3 days). Net assimilation rate (AN), stomatal conductance (gs), substomatal CO2 concentration (Ci), transpiration rate (E), actual photochemical efficiency of PSII (ΦPSII), and maximum photochemical efficiency of PSII (Fv/Fm) were recorded by combining measurements of gas exchange and chlorophyll fluorescence. Gross photorespiration (Pr), photosynthetic electron partitioning (JC/JT), photochemical quenching coefficient (qP), and non-photochemical quenching (NPQ) were also calculated. The ratio of net assimilation rate to transpiration rate (AN/E) was used as an indicator of water use efficiency (WUE). AN, apparent Pr, ΦPSII, Fv/Fm, qp, and gs decreased, NPQ increased, and gross Pr sustained at a high level under water stress. This suggests that both photorespiration and energy dissipation play important roles in protecting photosynthetic apparatus against photoinhibition. Ci in water-stressed plants without adaptation treatment increased, which indicates the leaves suffered a non-stomatal limitation, while the water-stress adaped plants only suffered a stomatal limitation indicated by low Ci. and X. Guan, S. Gu.
Primary leaves of bean (Phaseolus vulgaris L.) seedlings cultivated for 14 days in a growth chamber on complete (control) and phosphate deficient (-P) Knop liquid medium were used for measurements. The -P leaves were smaller and showed an increased specific leaf area (SLA). Their inorganic phosphate (Pi) concentration was considerably lowered. They did not show any significant changes in chlorophyll (Chl) (a + b) concentration and in their net CO2 assimilation rate when it was estimated under the conditions close to those of the seedlings growth. Light response curves of photosynthetic net O2 evolution (P NO2) of the leaves for the irradiation range up to 500 μmol(photon) m-2 s-1 were determined, using the leaf-disc Clark oxygen electrode. The measurements were taken under high CO2 concentration of about 1 % and O2 concentrations of 21 % or lowered to about 3 % at the beginning of measurement. The results obtained at 21 % O2 and the irradiations close to or higher than those used during the seedlings growth revealed the phosphorus stress suppressive effect on the leaf net O2 evolution, however, no such effect was observed at lower irradiations. Other estimated parameters of P NO2 such as: apparent quantum requirement (QRA) and light compensation point (LCP) for the control and -P leaves were similar. However, with a high irradiation and lowered O2 concentration the rate of P NO2 for the -P leaves was markedly higher than that for the control, in relation to both the leaf area and leaf fresh mass. This difference also disappeared at low irradiations, but the estimated reduced QRA values indicate, under those conditions, the increased yield of photosynthetic light reaction, especially in the -P leaves. The presented results confirm the suggestion that during the initial phase of insufficient phosphate feeding the acclimations in the light phase of photosynthesis, both structural and functional appear. They correspond, probably, to the increased energy costs of carbon assimilation under phosphorus stress, e.g. connected with raised difficulties in phosphate uptake and turnover and enhanced photorespiration. Under the experimental conditions especially advantageous for the dark phase of photosynthesis (saturating CO2 and PAR, low O2 concentration), those acclimations may be manifested as an enhancement of photosynthetic net O2 evolution. and B. Kozłowska-Szerenos, A. Jarosz, S. Maleszewski.
The dynamics of the terrestrial ecosystems depend on interactions between a number of biogeochemical cycles (i.e. carbon, nutrient, and hydrological cycles) that may be modified by human actions. Conversely, terrestrial ecosystems are important components of these cycles that create the sources and sinks of important greenhouse gases (e.g. carbon dioxide, methane, nitrous oxide). Especially, carbon is exchanged naturally among these ecosystems and the atmosphere through photosynthesis, respiration, decomposition, and combustion processes. Continuous increase of atmospheric carbon dioxide (CO2) concentration has led to extensive research over the last two decades, during which more then 1 400 scientific papers describing impacts of elevated [CO2] (EC) on photosynthesis have been published. However, the degree of response is very variable, depending on species, growing conditions, mineral nutrition, and duration of CO2 enrichment. In this review, I have summarised the major physiological responses of plants, in particular of trees, to EC including molecular and primary, especially photosynthetic, physiological responses. Likewise, secondary (photosynthate translocation and plant water status) and tertiary whole plant responses including also plant to plant competition are shown.
The review is done to summarise the history of the discoveries of the many anatomical, agronomical, and physiological aspects of C4 photosynthesis (where the first chemical products of CO2 fixation in illuminated leaves are four-carbon dicarboxylic acids) and to document correctly the scientists at the University of Arizona and the University of California, Davis, who made these early discoveries. The findings were milestones in plant science that occurred shortly after the biochemical pathway of C3 photosynthesis in green algae (where the first chemical product is a three-carbon compound) was elucidated at the University of California, Berkeley, and earned a Nobel Prize in chemistry. These remarkable achievements were the result of ground-breaking pioneering research efforts carried out by many agronomists, plant physiologists and biochemists in several laboratories, particularly in the USA. Numerous reviews and books written in the past four decades on the history of C4 photosynthesis have focused on the biochemical aspects and give an unbalanced history of the multidisciplinary/multinstitutional nature of the achievements made by agronomists, who published much of their work in Crop Science. Most notable among the characteristics of the C4 species that differentiated them from the C3 ones are: (I) high optimum temperature and high irradiance saturation for maximum leaf photosynthetic rates; (II) apparent lack of CO2 release in a rapid stream of CO2-free air in illuminated leaves in varying temperatures and high irradiances; (III) a very low CO2 compensation point; (IV) lower mesophyll resistances to CO2 diffusion coupled with higher stomatal resistances, and, hence, higher instantaneous leaf water use efficiency; (V) the existence of the so-called "Kranz leaf anatomy" and the higher internal exposed mesophyll surface area per cell volume; and (VI) the ability to recycle respiratory CO2 by illuminated leaves.
Productivity of most improved major food crops showed stagnation in the past decades. As human population is projected to reach 9-10 billion by the end of the 21st century, agricultural productivity must be increased to ensure their demands. Photosynthetic capacity is the basic process underlying primary biological productivity in green plants and enhancing it might lead to increasing potential of the crop yields. Several approaches may improve the photosynthetic capacity, including integrated systems management, in order to close wide gaps between actual farmer’s and the optimum obtainable yield. Conventional and molecular genetic improvement to increase leaf net photosynthesis (P N) are viable approaches, which have been recently shown in few crops. Bioengineering the more efficient CC4 into C3 system is another ambitious approach that is currently being applied to the C3 rice crop. Two under-researched, yet old important crops native to the tropic Americas (i.e., the CC4 amaranths and the C3-CC4 intermediate cassava), have shown high potential P N, high productivity, high water use efficiency, and tolerance to heat and drought stresses. These physiological traits make them suitable for future agricultural systems, particularly in a globally warming climate. Work on crop canopy photosynthesis included that on flowering genes, which control formation and decline of the canopy photosynthetic activity, have contributed to the climate change research effort. The plant breeders need to select for higher P N to enhance the yield and crop tolerance to environmental stresses. The plant science instructors, and researchers, for various reasons, need to focus more on tropical species and to use the research, highlighted here, as an example of how to increase their yields., M. A. El-Sharkawy., and Obsahuje seznam literatury
Young (12 years old) Norway spruce {Picea abies [L.] Karst.) trees were exposed to ambient CO2 or ambient + 350 |niiol(C02) moL' continuously over 2 growing seasons in open-top chambers, under field conditions of a mountain stand. Comprehesive analysis of CO2 assimílation was performed after 4 and 22 weeks of the second growing season to evaluate the influence of elevated atmospheric CO2. A combination of gas exchange and a mathematical model of ribulose-l,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity was ušed. After 4 weeks of exposure no statistically significant stimulation of the radiant energy and CO2 saturated rate of CO2 uptake (ENsat) by the elevated CO2 concentration was found. Yet after 24 weeks a statistically significant depression of Ejvjsa, (38 %) and carboxylation efficiency (32 %) was observed. Depression of photosynthetic activity by elevated CO2 resulted from a decrease in the RuBPCO carboxylation rate. The electron transport rate was also modified similarly to the rate of RuBP formation. An accompanying decrease in nitrogen content of the needles (by 12 %) together with an increase in total saccharides (by 34 %) was observed after 24 weeks of exposure to enhanced CO2.
Five-year-old plants of two olive cultivars (Frantoio and Moraiolo) grown in large pots were exposed for 7 to 8 months to ambient (AC) or elevated (EC) CO2 concentration in a free-air CO2 enrichment (FACE) facility. Exposure to EC enhanced net photosynthetic rate (PN) and decreased stomatal conductance, leading to greater instantaneous transpiration efficiency. Stomata density also decreased under EC, while the ratio of intercellular (Ci) to atmospheric CO2 concentration and chlorophyll content did not differ, except for the cv. Moraiolo after seven months of exposure to EC. Analysis of the relationship between photosynthesis and Ci indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase after five months of exposure to EC. Based on estimates derived from the PN-Ci relationship, there were no apparent treatment differences in daytime respiration, CO2 compensation concentration, CO2-saturated photosynthetic rate, or photosynthetic rate at the mean Ci, but there was a reduction in stomata limitation to PN at EC. Thus 5-year-old olive trees did not exhibit down regulation of leaf-level photosynthesis in their response to EC, though some indication of adjustment was evident for the cv. Frantoio with respect to the cv. Moraiolo. and R. Tognetti ... [et al.].
Nowadays, a quest for efficient greenhouse heating strategies, and their related effects on the plant's performance, exists. In this study, the effects of a combination of warm days and cool nights in autumn and spring on the photosynthetic activity and efficiency of Phalaenopsis were evaluated; the latter, being poorly characterised in plants with crassulacean acid metabolism (CAM) and, to our knowledge, not reported before in Phalaenopsis. 24-h CO2 flux measurements and chlorophyll (Chl) fluorescence analyses were performed in both seasons on Phalaenopsis 'Hercules' exposed to relatively constant temperature regimes, 25.5/24.0°C (autumn) and 30/27°C (spring) respectively, and distinctive warm day/cool night temperature regimes, 27/20°C (autumn) and 36/24°C (spring), respectively. Cumulated leaf net CO2 uptake of the distinctive warm day/cool night temperature regimes declined with 10-16% as compared to the more constant temperature regimes, while the efficiency of carbon fixation revealed no substantial differences in both seasons. Nevertheless, a distinctive warm day/cool night temperature regime seemed to induce photorespiration. Although photorespiration is expected not to occur in CAM, the suppression of the leaf net CO2 exchange during Phase II and Phase IV as well as the slightly lower efficiency of carbon fixation for the distinctive warm day/cool night temperature regimes confirms the involvement of photorespiration in CAM. A seasonal effect was reflected in the leaf net CO2 exchange rate with considerably higher rates in spring. In addition, sufficiently high levels of photosynthetically active radiation (PAR) in spring led to an efficiency of carbon fixation of 1.06-1.27% which is about twice as high than in autumn. As a result, only in the case where a net energy reduction between the temperature regimes compensates for the reduction in net CO2 uptake, warm day/cool night temperature regimes may be recommended as a practical sustainable alternative. and B. Pollet ... [et al.].