Roles of Floral Organs and Phytohormones in Flower Stalk Elongation of Cymbidium (Orchidaceae)

Abstract

Effects of floral organs and phytohormones on the flower stalk elongation were investigated using a miniature Cymbidium hybrid (C. x Sazanami 'Haru-no-umi'). Complete excision of flower buds from an inflorescence greatly inhibited the elongation of the flower stalk (peduncle).When the basal two-thirds of flower buds on an inflorescence were removed, the flower stalk elongated nearly to the length of an intact peduncle. On the contrary, when the distal flower buds were excised, the upper part of the peduncle did not elongate. The elongation was also greatly reduced by removal of anthers alone or the entire perianths.
Under high temperature conditions that induce blasting of flower buds, 13-naphthaleneacetic acid (NAA) stimulated flower stalk elongation whether flower buds did or did not set. NAA also reversed the cessation of peduncle elongation caused by anther excision. However, this treatment did not promote flower opening. The application of gibberellic acid (GA3) stimulated both peduncle elongation and flower bud development, but the treatment failed to restore the elongation of peduncles from which flower buds were excised. These findings suggest that the peduncle elongation is stimulated mainly by auxin supplied from developing flower buds, especially from the anthers, and that flower bud development is primarily caused by gibberellin (GA). The elongation of the stalk is a secondary effect of developing floral parts brought about by GA.