The objective of the present investigation was to examine the extent of variations in single leaf net photosynthetic rate (PN) and its relative dependence on stomatal conductance (gs) and the mesophyll capacity to fix carbon in 12 clones of the natural rubber plant. There were significant variations in PN measured at low and saturating photon flux density (PFD); the extent of variation was larger at low than at saturating PFD. The compensation irradiance (CI) and apparent quantum yield of CO2 assimilation (φc) calculated from the PN/PFD response curves showed significant variations among the clones. PN at low irradiance was positively correlated with φc. Thus a clone with large PN at low irradiance, high φc, and low CI may tolerate shade better and thus produce a high tree stand per hectare. A strong positive correlation existed between PN saturated with radiant energy (Psat) and carboxylation efficiency (CE) estimated from the response curves of PN on intercellular CO2 concentration (Ci), but gs showed a poor correlation with Psat High CO2 compensation concentration (Γ) led to low CE in Hevea clones. A clone with large Psat, high CE, low gs, and low Γ is the one in which photosynthesis is more dependent on the mesophyll factors than stomata. Such a clone may produce relatively high biomass and maintain high water use efficiency. and K. N. Nataraja, J. Jacob.
Fifty-d-old poplar (Populus deltoides L.) plants were irrigated with 50-200 mM NaCl. 100 and 200 mM NaCl significantly reduced net photosynthetic rate, chlorophyll and carotenoid contents, leaf area, dry matter accumulation, and harvest index (HI) in all tested poplar clones (Bahar, S7C15, and WSL22). Clone S7C15 was more tolerant to salinity than the other clones. and M. Singh, M. Jain, R. C. Pant.
Among the three cultívars of tea, Assam hybrids had a relatively higher net photosynthetic rate (P^) than the China and Cambod types. Though the leaves selected for chlorophyll (Chl) estimation were physiologically mature and identical, wide range of shades in the colour of leaves was observed. No significant difference between cultívars was notíced in Chl (a + b) content, but distinct difference was obtained among certain dones. Chl atb ratío exhibited significant difference between both the cultívars and dones.
Photosynthesis, photorespiration, and chlorophyll (Chl) fluorescence in green and red Berberis thunbergii leaves were studied with two different measuring radiations, red (RR) and "white" (WR). The photosynthetic and photorespiration rates responded differently to the different radiation qualities, which indicate that the carboxylase and oxygenase activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were affected. Differences in photosynthetic rate between the two color leaves were less under RR than under WR. However, this reduced difference in photosynthetic rate was not correlated with the stomatal response to the measuring radiation qualities. Compared with the WR, the RR reduced the differences in dark-adapted minimum and maximum fluorescence, steady-state fluorescence, light-adapted maximum fluorescence, and actual photochemical efficiency (ΦPS2) of photosystem 2 (PS2), but enlarged the difference in non-photochemical quenching between the two color leaves. Differences in both maximum quantum yield of PS2 and ratio of ΦPS2 to quantum yield of CO2 fixation between the two color leaves were similar under the two measuring radiations. To exclude disturbance of radiation attenuation caused by anthocyanins, it is better to use RR to compare the photosynthesis and Chl fluorescence in green versus red leaves. and P.-M. Li ... [et al.].
Gas exchanges and leaf water potential (Ψw) of six-years-old trees of fourteen Prunus amygdalus cultivars, grafted on GF-677, were studied in May, when fruits were in active growing period, and in October, after harvesting. The trees were grown in the field under rain fed conditions. Predawn Ψw showed lower water availability in October compared with May. The lowest Ψw values at midday in May increased gradually afterwards, while in October they decreased progressively until night, suggesting a higher difficulty to compensate the water lost by transpiration. However, relative water content (RWC) measured in the morning was similar in both periods, most likely due to some rainfall that occurred in September and first days of October that could be enough to re-hydrate canopy without significantly increasing soil water availability. The highest net photosynthetic rate (PN) was found in both periods early in the morning (08:00-11:00). Reductions in PN from May to October occurred in most cultivars except in José Dias and Ferrastar. In all cultivars a decrease in stomatal conductance (gs) was observed. Photosynthetic capacity (Pmax) did not significantly change from spring to autumn in nine cultivars, revealing a high resistance of photosynthetic machinery of this species to environmental stresses, namely high temperature and drought. Osmotic adjustment was observed in some cultivars, which showed reductions of ca. 23 % (Duro d' Estrada, José Dias) and 15 % (Tuono) in leaf osmotic potential (Ψπ). Such decreases were accompanied by soluble sugars accumulation. The Portuguese cultivar José Dias had a higher photosynthetic performance than the remaining genotypes. and M. C. Matos ... [et al.].
Under a moderate water stress (pod water potential, Ψ№, - 1.5 MPa), induced by stopping irrigation for 3 d, the net photosynthetic rate (PN) decreased to 50 %, transpiration rate (£) to 85 %, stomatal conductance to 65 % and chlorophyll (Chi) content to 82 %, while the activities of photosystems (PS) and of some enzymes of the photosynthetic carbon reduction cycle (NAD- and NADP-glyceraldehyde-3-P dehydrogenases, aldolase) were almost without changes. The exceptions were ribulose-5-P kinase and 3-phosphoglycerate kinase, the activities of which were reduced to 55 and 79 %, respectively. Under a severe water stress (5 d without irrigation, VPW -2.1 MPa) all the above characteristics were strongly reduced (PN to 0.5 %, E to 57 %, PS1 to 62 %, PS2 to 37 %, enzyme activities to 48-68 %), but after rehydration the initial activities were restored. The reduction of PN in pods at a moderate water stress is probably related to the decline in activities of 3-phosphoglycerate kinase and ribulose-5-P kinase, while under a severe stress, when PN is lowered almost to zero, the decline in gs and electron transport activities is very important.
Most organisms inhabiting earth feed directly or indirectly on the products synthesized by the reaction of photosynthesis, which at the current atmospheric CO2 levels operates only at two thirds of its peak efficiency. Restricting the photorespiratory loss of carbon and thereby improving the efficiency of photosynthesis is seen by many as a good option to enhance productivity of food crops. Research during last half a century has shown that several plant species developed CO2-concentrating mechanism (CCM) to restrict photorespiration under lower concentration of available CO2. CCMs are now known to be operative in several terrestrial and aquatic plants, ranging from most advanced higher plants to algae, cyanobacteria and diatoms. Plants with C4 pathway of photosynthesis (where four-carbon compound is the first product of photosynthesis) or crassulacean acid metabolism (CAM) may consistently operate CCM. Some plants however can undergo a shift in photosynthetic metabolism only with change in environmental variables. More recently, a shift in plant photosynthetic metabolism is reported at high altitude where improved efficiency of CO2 uptake is related to the recapture of photorespiratory loss of carbon. Of the divergent CO2 assimilation strategies operative in different oraganisms, the capacity to recapture photorespiratory CO2 could be an important approach to develop plants with efficient photosynthetic capacity. and S. K. Vats, S. Kumar, P. S. Ahuja
Activity of carbonic anhydrase (CA) was studied in wild type (WT) Chlamydomonas reinhardtii and five mutants distinguished only by retaining photosystem 1 (PS 1), photosystem 2 (PS 2), light-harvesting complexes (LHC) of PS 1 or PS 2 and both photosystems without LHC. Two forms of CA, soluble CA (sCA) and membrane- bound (mbCA), were found in the cells. The highest activity of mbCA was obseiwed in mutants which retained both photosystems, oř only PS 1 and PS 2. The mutants deprived of photosystems but retaining LHC almost lacked mbCA. Thus, there was a correlation between the retention of mbCA and mutant abilities to perform the photosynthesis. Photosynthetic characteristics of the high CO2 requiring mutant of C. reinhardtii CIA-3 were compared with those of WT grown at 2 % CO2 and after various times of exposure to limiting CO2 concentration (0.03 %). CIA-3 cells háve a lower photosynthetic affmity for inorganic carbon (Cj) as compared to WT when grown at high and low CO2 concentrations. Only in the WT cells the photosynthetic affmity for Cj was increased when the gas phase was changed to air. In CIA-3 the photosynthesis was inhibited by a high concentration of Cj.