Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280-320 nm; 60 µmol m-2 s-1) exposure alone and in combination with photosynthetically active radiation (PAR; 400-800 nm; 200 µmol m-2 s-1) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O2 evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development and the ability was modified in UV-B+ PAR exposed samples. and M. K. Pradhan ... [et al.].
The effects of iso-osmotic salinity and drought stresses on leaf net photosynthetic rate (PN) in two wheat (Triticum aestivum L.) cultivars BR 8 and Norin 61, differing in drought tolerance, were compared. In drought-sensitive Norin 61, the decline of PN was larger than that in drought-tolerant BR 8. Under NaCl treatment, PN decreased in two phases similarly in both cultivars. In the first phase, photosynthetic depression was gradual without any photochemical changes. In the second phase, photosynthetic depression was rapid and accompanied with a decline of the energy conversion efficiency in photosystem 2 (ΦPS2). Our observations suggest that the osmotic factor may induce a gradual depression of photosynthesis due to stomatal closure under both stress treatments. However, under NaCl treatment, a ionic factor (uptake and accumulation of excess Na+) may have direct effects on electron transport and cause more severe photosynthetic depression. The drought tolerance mechanism of BR 8 was insufficient to maintain single-leaf photosynthesis under salinity. and S. Muranaka, K. Shimizu, M. Kato.
Fluorescence microscopy and physiological examination revealed the presence of an inner cylinder of active photosynthetic cells located below the endodermis-like layer in stems of four of the six taxa of the tribe Salicornieae (Chenopodiaceae). and S. Redondo-Gómez ... [et al.].
Nitrogen is an essential factor for normal plant and algal development. As a component of nucleic acids, proteins, and chlorophyll (Chl) molecules, it has a crucial role in the organization of a functioning photosynthetic apparatus. Our aim was to study the effects of nitrogen starvation in cultures of the unicellular green alga, Chlamydomonas reinhardtii, maintained on nitrogen-free, and then on nitrogen-containing medium. During the three-week-long degreening process, considerable changes were observed in the Chl content, the ratio of Chl-protein complexes, and photosynthetic activity of the cultures as well as in the ultrastructure of single chloroplasts. The regreening process was much faster then the degradation; total greening of the cells occurred within four days. The rate of regeneration depended on the nitrogen content. At least 50% of the normal nitrogen content of Tris-Acetate-Phosphate (TAP) medium was required in the medium for the complete regreening of the cells and regeneration of chloroplasts., É. Preininger, A. Kósa, Z. S. Lőrincz, P. Nyitrai, J. Simon, B. Böddi, Á. Keresztes, I. Gyurján., and Obsahuje seznam literatury