The Influence of Increased Solar UV-B Radiation on Magnesium-Deficient Cowpea Seedlings: Changes in the Photosynthetic Characteristics

The influence of increased solar UV-B radiation on the photosynthetic characteristics in cowpea seedlings (Vigna unguiculata) grown at optimal (Mg_s) and low (Mg_d) Mg levels were studied. Both higher UV-B and Mg_d treatments caused significant drops of photochemical activities and net CO₂ uptake rates (P_N). Yet the UV-B-induced decrease in the photosynthetic efficiency was lesser in Mg_d seedlings. The leaf Chl 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 remarkably altered by both treatments. The P_N also followed a typical inhibitory pattern as seen in photochemical activities. Concentrations of several chloroplast proteins in trifoliate leaves were significantly reduced by Mg_d 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 Mg_d seedlings, no major difference was noted for combined stress. This revised version was published online in September 2006 with corrections to the Cover Date.