HORMONE MUTANTS IN HIGHER-PLANTS - CHARAC TERIZATION OF CYTOKININ-RESISTANT MUTANTS OF NICOTIANA-PLUMBAGINIFOLIA

Progress in understanding the modes of phytohormone action have now be en obtained using a genetic approach. This was illustrated here by the study of the cytokinin-resistant mutants zea isolated in Nicotiana pl umbaginifolia (Jullien et al., 1990). The resistance to cytokinins con ferred by the zea mutations is expressed in different ways. At the pla ntlet and seedling level, ca 1 muM cytokinin stimulated the growth of the mutants. At higher concentrations, the seedlings of the mutants sh ow a pronounced hypertrophy of the hypocotyl and cotyledons when the w ild type were inhibited. Mutants grew faster than the wild type on bas al medium containing sucrose. Tissues of the mutant plantlets grown in these conditions contained less sucrose and more glucose, fructose, s tarch and malate than the wild type plantlets. The malate level in som e of the mutants zea appeared very sensitive to cytokinins.