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 this paper we show that during this process, ABA rapidly induces elevated levels of mRNA transcripts encoding a novel basic peroxidase. In addition, we show that in the presence of the cytokinin kinetin the maintained increase is attenuated. Kinetin not only totally inhibits the induction of turions by ABA but also alleviates ABA-induced growth inhibition. This antagonism of an ABA-induced gene by a cytokinin correlates with an easily observable antagonistic effect of these two hormones on plant morphogenesis. These data contribute to a growing body of evidence linking growth regulators with changes in peroxidase gene expression and to the concept of pairs of hormones playing antagonistic roles during plant development. Finally, we discuss the possible functions that peroxidases could have during ABA-induced turion formation and growth inhibition.