THE ABSCISIC-ACID INDUCTION OF A NOVEL PEROXIDASE IS ANTAGONIZED BY CYTOKININ IN SPIRODELA-POLYRRHIZA L

The growth regulator abscisic acid (ABA) can be used to induce dormant bud structures (turions) in the duckweed Spirodela polyrrhiza L. In t his paper we show that during this process, ABA rapidly induces elevat ed levels of mRNA transcripts encoding a novel basic peroxidase. In ad dition, we show that in the presence of the cytokinin kinetin the main tained increase is attenuated. Kinetin not only totally inhibits the i nduction of turions by ABA but also alleviates ABA-induced growth inhi bition. This antagonism of an ABA-induced gene by a cytokinin correlat es with an easily observable antagonistic effect of these two hormones on plant morphogenesis. These data contribute to a growing body of ev idence linking growth regulators with changes in peroxidase gene expre ssion and to the concept of pairs of hormones playing antagonistic rol es during plant development. Finally, we discuss the possible function s that peroxidases could have during ABA-induced turion formation and growth inhibition.