AMP1 - A MUTANT WITH HIGH CYTOKININ LEVELS AND ALTERED EMBRYONIC PATTERN, FASTER VEGETATIVE GROWTH, CONSTITUTIVE PHOTOMORPHOGENESIS AND PRECOCIOUS FLOWERING

amp1, a mutant of Arabidopsis thaliana has a phenotype altered in thre e different aspects of plant development; spatial pattern, photomorpho genetic growth, and initiation of flowering. While fewer than 0.1% of the seedlings of wild-type plants are non-dicot as many as 20% of the seedlings of the amp1 mutant are tricot or tetracot. The rate of leaf initiation is faster and vegetative phyllotaxy is altered in amp1. Whe n grown in the dark amp1 seedlings show morphogenetic properties simil ar to light-grown wild-type plants: they do not form an apical hook, h ave hypocotyls shorter than wild-type plants and form etiolated true l eaves. amp1 mutant flowers significantly earlier than congenic Amp1 pl ants. The mutant has six times more cytokinin than wild-type suggestin g that endogenous cytokinin levels might play an important role in med iating these different developmental processes. AMP1 might code for a negative regulator of cytokinin biosynthesis, or may be required for t he degradation of cytokinin.