Water deficit, when rapidly imposed on three C4 grasses of the different metabolic subtypes, Paspalum dilatatum Poiret (NADP-malic enzyme), Cynodon dactylon (L.) Pers (NAD-malic enzyme) and Zoysia japonica Steudel (phosphoenolpyruvate carboxykinase), caused decreases in photosynthetic rates, in the quantum yield of PS II and photochemical quenching, and in the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC). The results provide evidence for non-stomatal limitations of photosynthesis differing in nature between the three species. and A. S. Soares-Cordeiro ... [et al.].
The influence of viral infection caused by two different potyviruses, Potato virus Y (PVY) and Potato virus A (PVA) on plant metabolism and photosynthetic apparatus of Nicotiana tabacum L. cv. Samsun and cv. Petit Havana SR1 was studied. The main stress was focused on the activities of phosphoenolpyruvate carboxylase (PEPC), NADP-malic enzyme (NADP-ME), and pyruvate phosphate dikinase (PPDK). The analysis of the presence of viral proteins, enzyme activities, and different photosynthetic parameters showed the time dependent progress of viral infection and NADP-ME and PEPC activities. PVY caused significant response, while PVA affected both tobacco cultivars only slightly. Viral infection, namely PVY, affected more negatively photosynthetic apparatus of cv. Petit Havana SR1 than cv. Samsun. and H. Ryšlavá ... [et al.].
Biao 810S is a chlorina mutant of the thermosensitive genic male sterile (TGMS) rice. We compared photosynthetic characteristics of these two lines. The contents of chlorophylls and carotenoids in Biao 810S were approximately half of those in 810S. However, the net photosynthetic rate (PN) of Biao 810S was higher than that of 810S under high irradiance or low concentration of carbon dioxide, and the photon quantum efficiency was higher than that of 810S. The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in Biao 810S was only 69.80 % of that in 810S, but the activities of phosphoenolpyruvate carboxylase and NADP-malic enzyme were 79.50 and 69.06 % higher than those of 810S, respectively, suggesting that the efficiency of photon energy utilization in Biao 810S was enhanced by reduction of thermal dissipation and increase of electron transfer rate to generate sufficient assimilation power for the dark reactions. Consequently, the increased activities of C4 photosynthetic enzymes lead to more effective fixation of CO2 and the synergistic effect of light and dark reactions contributed to the higher PN of Biao 810S. and L.-J. Ou ... [et al.].
Two stress imposing systems were used: a rapid stress developed by allowing excised leaves to loose water by transpiration, and a slow stress developed by withholding watering of potted plants. Carboxylating enzymes reacted differently on both types of stress. Rapid stress increased ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activation, but both activities (initial and total) showed little variation with stress. Under slow stress the activation did not change, although both activities decreased much under stress. Phosphoenolpyruvate carboxylase (PEPC) showed a deep decrease of activity under rapid stress, nevertheless, a certain recovery was found under extreme stress. On the other hand, under slow stress the activity of PEPC showed a linear increase with decreasing relative water content. The ratio between physiological and maximal activity increased slightly under both types of stress. The activity of malic enzyme did not change under rapid stress, and decreased linearly under slow stress. and J. Marques da Silva, M. C. Arrabaça.