Formation of epiphyllous buds in sunflower ( Helianthus annuus L.): induction in vitro and cellular origin

Abstract

Epiphyllous buds developed on leaves of shoots derived from in vitro cultured apices of sunflower ( Helianthus annuus L.) seedlings. This phenomenon was shown to be cytokinin-dependent but only occurred when the cytokinin was supplied via the cultured apices producing the leaf-bearing shoots. A 1-day exposure of apices to cytokinin was sufficient for epiphyllous bud induction, although an exposure of more than 4 days yielded maximal shoot development frequencies from these buds. Preculture of complete donor seedlings on cytokinin-supplemented media and subsequent culture of excised leaves on hormone-free medium was insufficient 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 originating 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.