INDUCTION OF ENZYMES ASSOCIATED WITH LYSIGENOUS AERENCHYMA FORMATION IN ROOTS OF ZEA-MAYS DURING HYPOXIA OR NITROGEN STARVATION

Either hypoxia, which stimulates ethylene biosynthesis, or temporary N starvation, which depresses ethylene production, leads to formation o f aerenchyma in maize (Zea mays L.) adventitious roots by extensive ly sis of cortical cells. We studied the activity of enzymes closely invo lved in either ethylene formation (1-aminocyclopropane-1-carboxylic ac id synthase [ACC synthase]) or cell-wall dissolution (cellulase). Acti vity of ACC synthase was stimulated in the apical zone of intact roots by hypoxia, but not by anoxia or N starvation. However, N starvation, as well as hypoxia, did enhance cellulase activity in the apical zone , but not in the older zones of the same roots. Cellulase activity did not increase during hypoxia or N starvation in the presence of aminoe thoxyvinylglycine, an inhibitor of ACC synthase, but this inhibition o f cellulase induction was reversed during simultaneous exposure to exo genous ethylene. Together these results indicate both the role of ethy lene in signaling cell lysis in response to two distinct environmental factors and the significance of hypoxia rather than anoxia in stimula tion of ethylene biosynthesis in maize roots.