Induction of flowering in a duckweed ? Wolffia microscopica ? By a new kinin, zeatin

Abstract

Success in induction of flowering, particularly in short-day plants, by chemical means is still a rare phenomenon. Among plants of this class, Perilla nankinensis and Chrysanthemum morifolium are perhaps the only two examples where flowering has been induced under non inductive conditions. In Perilla cultured shoot apices turned reproductive when kinetin and adenine were included in the medium (Chailakhian, 1961); in Chrysanthemum GA applied to plants brought about the same effect (Barbat and Ochesanix, 1964). We report here that zeatin, a new kinin, has a marked effect in initiating flowers in a short-day plant — Wolffia microscopica — under long-day conditions. This we believe to be interesting not only from the viewpoint of the role of zeatin in plants in general, but also of the physiology of flowering since few substances of equivalent potency in inducing flowering are yet known. Zeatin, it may be added is chemically known as 6-(4-hydroxy-3-methyl but-2-enyl) aminopurine, and was recently isolated by Le-tham (1963) from the immature seeds of Zea mays. The plants of Wolffia microscopica, which are about the size of a pinhead, are ideally suited for investigations on flowering (Maheshwari and Chauhan, 1963). They were aseptically cultured on medium containing Hoagland's major salts and Heller's micronutrients supplemented with 5 X 10~5 M EDTA and 1 % sucrose. The medium contained the following salts (mg/1): KN03506, Ca(N03)2-4H201180, KH2P04136, MgS04-7H20 493, ZnS04-7H20 1, H3B03 1, MnS04H20 0.1, CuS04-5H20 0.03, Na2Mo04-2H20 0.025 and 4 mg of ferric citrate. The pH of the medium was adjusted to 5.5. Plants obtained from a single clone were used for the investigation. The plants were kept at 25° C (± 1°C) under a photoperiodic regime consisting of 20hours of light (550—600 f t-c) and 4 hours of darkness. Under these conditions their number doubles every 24 hours through vegetative multiplication but there is no flowering. The incorporation of zeatin caused some decrease in the multiplica tion rate. However, the growth of individual plants was greatly accelera ted. An increase in the size of the fronds was apparent even on the fourth