Ribonuclease activity as an index of hidden hunger of zinc in crops

Summary The activity of RN-ase at zero zinc level was found to be 2, 173-1 and 2 times higher in all the varieties of rice (Jaya and HM484) and Maize (Ganga 5 and Vijay) than that of 5 ppm zinc at 15/20 days, 30/40 days and 45/60 days growth stages respectively, but the difference in the zinc content of leaves between two treatments was not found to be significant except that of 30/40 days growth stage. Similarly the potash content in both the treatments did not vary, but the dry matter production of whole plant and protein content of leaves except 15/20 days growth stage varied significantly. The data suggest thirty ppm P released per 100 g protein per hour (RN-ase activity) could be taken as threshold value above which hidden deficiency at an early growth stage is detected. Also an average concentration of 27 and 25 ppm zinc in rice and maize leaves respectively could be taken as critical limit for zinc deficiency at their 15/20 days of growth respectively. On the basis of RN-ase activity the hidden hunger of zinc in crop can be predicted at an early growth stage (15/20 days) where the zinc content in plant tissue fail to reveal the true picture of zinc deficiency.