AN HYPOTHESIS OF THE ROLE OF NAPHTHALENEACETIC ACID IN FLOWER INDUCTION IN THE PINEAPPLE

Abstract

THE USE OF the sodium salt of naphthaleneacetic acid (SNA) to induce flowering in the pineapple piant has been a commercial practice in the Hawaiian Islands for a number of years (van Overbeek, 1951). Although the use of naphthaleneacetic acid and other auxins has been studied extensively in connection with plants sensitive to photoperiod, little has been published concerning its role in the flowering of the pineapple, a day-neutral plant under Hawaiian conditions. It is the purpose of this paper to present some evidence in support of an hypothesis of the behavior of SNA in flower induction of the pineapple, Ananus comosuts (L.) Merr. var. 'Smooth Cayenne.' For some time it has been recognized that the level of auxin in plant tissues may influence the differentiation and growth of such widely different organs as stems, roots, and vegetative buds, and that the concentration of auxin which stimulates one may inhibit another (Thimann, 1937). That flowering, too, may be primarily a response to effective auxin level was demonstrated by Leopold and Thimann (1949)with particular reference to Wintex barley (a long-day plant) during inductive treatment. It was proposed by Bonner aind Liverman (1953) that, in inducing flowering in the pineapple, naphthaleneacetic acid and 2,4-dichlorophenoxyacetic acid might be acting as antiauxins rather than as auxins-antagonistically to the native auxin. In this connection, it is of interest to note that indoleacetic acid (IAA) is a native auxin in the pineapple plant, as shown by Gordon and Nieva (1949). As a working hypothesis, it is proposed that (1) there is a range of auxin concentration within which flower formation occurs and outside of which flowering does not occur. (2) Application of SNA (or other synthetic auxins) acts to lower the effective native auxin concentration in the stem tip by competing for sites of auxin activity. (3) Indoleacetic acid (IAA) is the native auxin of importance in pineapple flowering. Plant oxidases destroy both the added auxins and IAA, but the plant resynthesizes IAA, so that (4) the activity of plant oxidases in removing added auxins may be considered to control the length of time the effective IAA concentration remains within the flowering range.