ACCUMULATION OF A GENE-SPECIFIC MESSENGER-RNA IN RESPONSE TO CYTOKININ TREATMENT OF LEAVES IN PHASEOLUS-VULGARIS

The abundance of the transcripts of certain plant genes increases in r esponse to cytokinin treatments in vitro. This study was conducted to determine whether one such transcript would respond to cytokinin treat ment in planta. Cytokinin treatment of the leaves of Phaseolus vulgari s L. plants grown in the greenhouse stimulated the accumulation of an mRNA, designated L-22, by approximately 4-fold within 4 h in replicate d experiments. The extent of the L-22 transcript accumulation was in l ogarithmic relation to the dose of cytokinin applied between 10 mu M a nd 1 mM, however the mRNA accumulation was transient. Therefore, trans cript abundance was regulated in response to both the dose of cytokini n applied and the event of a change in cytokinin concentration in trea ted leaves. The extent of mRNA accumulation differed only slightly dep ending on the structure of the cytokinin applied indicating only small differences among the activities of cytokinins used in this assay. Am ong the plant growth regulators tested only cytokinin caused the mRNA to accumulate, suggesting the response was cytokinin specific. The ded uced amino acid sequence of the L-22 protein product, derived from the nucleotide sequence of the L-22 cDNA, was up to 24% identical and 49% similar to the gamma subunit of mitochondrial H+-transporting ATP syn thase (EC 3.6.1.34) in the conserved, catalytic, carboxyl-terminal dom ain. Therefore, the L-22 protein product may have a role in the regula tion of processes related to plant respiration by cytokinin.