Phyllotaxis of vegetative shoots of Anagallis arvensis L. treated in vitro with 6-benzylaminopurine

Application of 6-benzylaminopurine (BA), a synthetic cytokinin, to the growth medium in vitro stimulates the formation of adventitious shoots on stem explants of Anagallis arvensis. They regenerate from dedifferentiating epidermal cells of stem internodes. The process starts from periclinal and anticlinal divisions in a few of neighbouring cells. The amount of adven-titious shoots increases with an increasing BA concentration. The BA treatment also affects phyllotaxis, but only of adventitious shoots, and not of normal lateral shoots developing in leaf axils. Leaf arrangement on adventitious shoots is always variable, even on the control medium. Generally, patterns observed in case of in vitro shoots do not differ from those reported earlier for intact A. arvensis plants. BA treatment also leads to the teratologic development, i.e. fasciation and the formation of abnormally shaped leaves, but again in adventitious rather than in normally developing shoots. We postulate that the variability of phyllotaxis characteristic for adventitious shoots and their responce to BA treatment, result from the fact that their apical meristems develop de novo from initially unorganised meristematic centres, whereas meristems of normally developing lateral shoots are well organised from the time of their initiation.