FORMATION OF EPIPHYLLOUS BUDS IN SUNFLOWER (HELIANTHUS-ANNUUS L.) - INDUCTION IN-VITRO AND CELLULAR-ORIGIN

Epiphyllous buds developed on leaves of shoots derived from in vitro c ultured apices of sunflower (Helianthus annuus L.) seedlings. This phe nomenon was shown to be cytokinin-dependent but only occurred when the cytokinin was supplied via the cultured apices producing the leaf-bea ring shoots. A I-day exposure of apices to cytokinin was sufficient fo r epiphyllous bud induction, although an exposure of more than 4 days yielded maximal shoot development frequencies from these buds. Precult ure of complete donor seedlings on cytokinin-supplemented media and su bsequent culture of excised leaves on hormone-free medium was insuffic ient to induce epiphyllous bud formation. Buds became macroscopically visible after 9-11 days. At this time, epiphyllous buds consisted of a functional meristem producing true shoots which were capable of seed production. The meristems were formed by a multicellular process origi nating from subepidermal layers on the adaxial leaf side. The role of cytokinin and other potential factors in the induction of epiphyllous buds on sunflower leaves is discussed. (C) 1998 Elsevier Science Irela nd Ltd. All rights reserved.