Carotenoids (Car) regulate energy flow in photosynthesis by a specific Car-chlorophyll (Chl) interaction in the singlet-excited states, leading to a reduction in Chl fluorescence. We studied quenching of Chl a-fluorescence in benzene by trans-β-carotene. Non-linear analysis of the quenching process enables to explain the possible molecular mechanism leading to the de-excitation of Chl a. The fluorescence intensity was measured at 670 nm for excitation wavelengths of 380, 430, 640, and 650 nm. The β -carotene concentrations ranged from 4×10-5 M to 5×10-3 M. When the samples were excited at 640 and 650 nm, the Stern-Volmer plots showed that the quenching process has high rate constants, hence β-carotene is a very efficient quencher. Two different types of quenching process could take place. and D. M. Gazdaru, B. Iorga.
Caragana korshinskii Kom. is a perennial xerophytic shrub, well known for its ability to resist drought. In order to study ecophysiological responses of C. korshinskii under extreme drought stress and subsequent rehydration, diurnal patterns of gas exchange and chlorophyll (Chl) fluorescence parameters of photosystem II as well as Chl content were analyzed. Plant responses to extreme drought included (1) leaf abscission and using stem for photosynthesis, (2) improved instantaneous water-use efficiency, (3) decreased photosynthetic rate and partly closed stomata owing to leaf abscission and low water status, (4) decreased maximum photochemical efficiency of photosystem II (PSII) (variable to maximum fluorescence ratio, Fv/Fm), quantum efficiency of noncyclic electron transport of PSII, and Chl a and Chl b. Four days after rehydration, new leaves budded from stems. In the rewatered plants, the chloroplast function was restored, the gas exchange and Chl fluorescence returned to a similar level as control plant. The above result indicated that maintaining an active stem system after leaf abscission during extreme drought stress may be the foundation which engenders these mechanisms rapid regrowth for C. korshinskii in arid environment., D. H. Xu ... [et al.]., and Obsahuje bibliografii
Changes in photosynthetic attributes related to genetic improvement of cotton yield were studied in seven Chinese cotton cultivars widely grown in Xinjiang during the past 30 years. Our results showed that a chlorophyll (Chl) content and net photosynthetic rate (PN) of the 1980s cultivar was the highest among all after 60 days from planting (DAP). However, after 75 DAP, the Chl content, PN, and actual photochemical efficiency of PSII of the old cultivars declined gradually, whereas those of the new cultivars remained relatively high. Compared to the old cultivars, leaves of the new cultivars endured a longer period and their senescence was slower, shoot and boll dry mass was higher, but the root to shoot ratio was lower. The lint yield of the 2000s cultivars was 14.7 and 21.4% higher than that of 1990s and 1980s cultivars, respectively. The high yield of the new cultivars was attributed to a greater number of bolls per unit of area with high lint percentage. We suggested that the improved photosynthetic capacity and the increased ability to deliver photosynthates to reproductive sites during the peak boll-setting stage to boll-opening stage were the key physiological basis in the evolution process of cotton cultivars from 1980s to 2000s for the cotton yield improvement within a short growing period., H. H. Luo, H. L. Zhang, Y. L. Zhang, W. F. Zhang., and Obsahuje bibliografii