IAA Inhibition of in vitro Flowering of the Short-Day Plant Streptocarpus nobilis. An Effect on Maintenance of Induction

Abstract

Summary Leaf explants from photoperiodically induced plants of the short-day plant Streptocarpus nobilis (C. B. Clarke) developed adventitious flower buds when cultured in non-inductive photo-periods. The degree of in vitro flowering correlated quantitatively with the number of short days received by the donor plant. The discrete states of induction, generated in response to various cycles of short days, were stable and served to assay the influence of IAA on the expression of the induced state in vitro . IAA was a very potent inhibitor of the expression of the induced state. In non-inductive photoperiods, IAA (5×10 −6 M) increased bud production three-fold and completely inhibited flower formation on explants of photoinduced leaves. In short days flowering was not inhibited by IAA and although IAA-mediated bud production was lower than in night-breaks IAA treatment resulted in an increased production of flower buds. Inhibition of flowering by IAA was due to degradation of the induced state in non-inductive photo-periods. Mechanisms by which IAA could modulate the expression of the photoperiodically induced flowering signal are discussed.