The influence of increased solar UV-B radiation on magnesium-deficient cowpea seedlings: changes in the photosynthetic characteristics

摘要

The influence of increased solar UV-B radiation on the photosynthetic characteristics in cowpea (Vigna unguiculata) seedlings grown at optimal (Mgs) and low (Mgd) Mg levels were studied. Both higher UV-B and Mgd treatments caused significant decreases in photochemical activities and net CO2 uptake rates (PN). The UV-B-induced decrease in photosynthetic efficiency was less in Mgd seedlings. Leaf chlorophyll a fluorescence measurements proved that after receiving an enhanced UV-B radiation these seedlings showed a significant enhancement in their variable parts. The PSM oscillation of slow fluorescence kinetics was markedly altered by both treatments. PN also followed a typical inhibitory pattern as seen in photochemical activities. Concentrations of several chloroplast proteins in trifoliate leaves were significantly reduced by Mgd treatment and unaffected by the other two treatments. Whereas the contents of 43-47 kDa polypeptides in primary leaves were markedly reduced, with a maximal effect in Mgd seedlings, no major difference was noted for combined stress.