THE PROMOTION OF FLORAL INITIATION BY AUXIN

Abstract

EVIDENCE CONCERNING the influence of auxin on flowering indicates that auxins can either promote or inhibit floral initiation in some plants. Inhibitions have been reported for a wide diversity of -species, including Xanthium, Kalanchoe, soybean, Helianthus tubero,sus, Eutchlaena, pineapple, barley, Calendula officinalis, Phalaenopsis schilleriana and others (cf. reviews by Lang, 1952; Liverman, 1955). Auxins have been shown to induce flowering in pineapple (Clark and Kerns, 1942; van Overbeek, 1946). Promotive effects of auxin on flowering have been reported only occasionally, and principally with long-day species, including Wintex barley (Leopold and Thimann, 1949) and Hyoscyamuis niger (Claes, 1952; Liverman and Lang, 1952). Only one short-day species has been reported to be promoted by auxin, the soybean (Leopold and Guernsey, 1953), and only at rather low temperatures. It is interesting to note that promotions of flowering have been obtained for short-day species so rarely, and in fact considerable importance has sometimes been attached to the concept that auxins apparently only inhibit floral initiation in these species. I Inhibitions of various growth functions occur generally with relatively high auxin concentrations, whereas promotive effects are obtained with low to very low auxin concentrations. If we are to seek promotive effects it would seem important to apply quite small amounts of auxin. In addition the question arises as to whether studies of the influence of auxin applied just during the flower-inducing treatment is sufficeient. It is reasonable to assume that a series of events is involved in the processes leading to floral initiation, and auxin may influence more than one of these events. Therefore, it seems attractive to apply the auxin not only during photoinduction, but alternatively before or immediately after photoinduction. The present work concerns the influence of the time and concentration of auxin application on flowering of two short-day species, cocklebur and Biloxi soybean. Evidence is brought forth that low auxin concentrations, applied before the short-day treatment, have a large promolive effect on flowering.