ROLE OF PUTRESCINE METABOLIC PATHWAYS IN THE DIFFERENTIATION PROCESS OF MAIZE MERISTEMATIC CALLUS

The role of putrescine and its interaction with auxin in modulating th e differentiation of maize meristematic callus was studied. The effect of exogenous putrescine on differentiation depends on the endogenous polyamine level of the callus and the stage at which putrescine was ap plies. Plant regeneration was highest in the 1 mM putrescine initiated the differentiation process with a higher endogenous putrescine conte nt versus control. The enzymatic activities of arginine and ornithine decarboxylase (responsible for putrescine synthesis) were considerably lower in the presence of exogenous putrescine, indicating a feed-back or a final product inhibition, respectively. The rise observed in the perchloric acid-insoluble polyamine fraction, especially putrescine, could be related to the initiation of the differentiation process. Low doses of auxin in differentiation medium induced a general decrease i n plant regeneration. However, activation of the differentiation proce ss was observed in calluses cultured in the presence of auxin and an e xcess of putrescine. In these calluses, the perchloric acid-soluble co njugated fraction increased significantly. These data indicate that pu trescine is involved in the endogenous regulation of callus morphogene sis. (C) Elsevier, Paris.