Manganese stress alters phytotoxic effects of chromium in green gram physiology (Vigna radiata L.) cv. PU 19

To see the effect of variable Mn on excess Cr, plants of green gram (Vigna radiata L.) cv. PU 19 were grown in refined sand. Plants were maintained previously at three levels of manganese, at 1 μM (deficient), 10 μM (adequate) and 500 μM (excess) for 47 days. After manifestation of Mn deficiency (40-45 days) as well as that of excess Mn (38-40 days), on 48th day excess Cr was superimposed on a set of these plants. On day 52 (5 days after metal supply) the Mn deficient plants with excess Cr exhibited interveinal chlorosis, which intensified with age. Similar symptoms of excess Cr appeared at adequate and excess Mn but were mild. Low Mn accentuated the effects of excess Cr by decreasing further the reduced biomass, concentration of iron, chlorophyll a and b, activity of ribonuclease and increased further that of peroxidase, whereas excess Mn increased Hill reaction activity and acid phosphatase activity more than low Mn.