INTERNAL ZINC ACCUMULATION IS CORRELATED WITH INCREASED GROWTH IN RICE SUSPENSION-CULTURE

A high zinc concentration of 520 mu M, approximately 100 times that us ed most often in standard plant tissue culture media, was found to be superior in liquid callus cultures of japonica rice, increasing growth to 146% compared with standard N6 medium. At the same time, the inter nal zinc concentration increased 40 times in fast growing cells; solub le protein doubled, and free amino acids decreased. Under zinc-free co nditions the cultures slowed in growth, and several free amino acids s uch as aspartic acid, glutamic acid, asparagine, and glutamine accumul ated. We suggest that zinc acts as a direct regulatory factor in induc ing auxin activity, but not auxin levels, making high internal zinc ac cumulation mandatory if high auxin concentrations are required as in r ice callus cultures.