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.].
Flooding stress (FS) induced changes in pigment and protein contents and in photochemical efficiency of thylakoid membranes of chloroplasts were investigated during senescence of primary leaves of rice seedlings. Leaf senescence was accompanied by loss in 2,6-dichlorophenolindophenol (DCPIP) photoreduction, rate of oxygen evolution, quantum yield of photosystem 2 with an increase in MDA accumulation, and non-photochemical quenching (NPQ) of chlorophyll fluorescence. These changes were further aggravated when the leaves during this period experienced FS. The increase in NPQ value under stress may indicate photosynthetic adaptation to FS. and S. K. Mishra ... [et al.].