MODULATION OF PLANT GENE-EXPRESSION BY CYTOKININS

Cytokinins play important roles in plant growth and development. They regulate the synthesis or degradation of proteins and nucleic acids. S pecific mRNAs and proteins are up- and down-regulated by the hormones. Regulation of plant gene expression by cytokinins is at the levels of transcription and post-transcription. Expression of a single gene can be modulated by the interaction of two hormones since the levels of c ytokinin-enhanced nitrate reductase transcript are reduced by abscisic acid. Relatively high-affinity cytokinin-binding proteins have been i solated, but the physiological role of the binding proteins remains un known. Examination of X-ray crystal structures of cytokinin molecules indicates that correct stereochemical conformation is required for a b iologically active cytokinin. Using available genetic, immunological, biochemical and recombinant DNA techniques, some questions regarding t he mechanisms of cytokinin action may be answered in the near future.