Cadmium and zinc induced chlorosis in Indian mustard [Brassica juncea (L.) Czern] involves preferential loss of chlorophyll b

Plants of Indian mustard (Brassica juncea) were treated with either 50 mu M Cd, 250 mu M Zn, or 25 mu M Cd+125 mu M Zn and the progression of chlorosis in the mature leaves monitored. As relative chlorophyll (Chl) contents in the mature leaves decreased to 75, 50, and 25 % relative to controls, both mature and young leaves were harvested and the Chl pools extracted. The metal treatments caused a greater loss of Chl b than Chl a. As mature leaves underwent progressive chlorosis, the young leaves displayed a characteristic over-greening, due largely to increased content of Chl b. However, as the young leaves began to experience chlorosis, a greater loss of Chl b was also observed. Thus during metal induced chlorosis, there is a preferential turnover of the Chl b pool in mature and young leaves.