Interaction of Daylength and Applied Gibberellins on Stem Growth and Leaf Production in Three Varieties of Celery

Abstract

Pressman, E. and Negbi, M. 1987. Interaction of daylength and applied gibberellins on stem growth and leaf production in three varieties of celery.—J. exp. Bot. 38: 968-971. Exogenous application of gibberellins (GAs) stimulated stem length. The extent of this stimulation was less in long photoperiods, as long days (LD) or as long nights interrupted by night breaks (NB), than it was in short days (SD). Long photoperiods increased the length and erectness of leaves and reduced leaf number. Similar morphological changes were stimulated by applied GAs, which were more effective on plants grown in SD than on those in LD. It is suggested that long photoperiods cause these morphological changes via the production or metabolism of endogenous GAs, but it is not clear how endogenous GAs interact with the applied Key words—Daylength, gibberellins, stem growth, leaf production, celery. Correspondence to: Department of Vegetable Crops, Agricultural Research Organization, The Volcani Centre, Bet Dagan, Israel. INTRODUCTION Celery (Apium graveolens L.) is a short-day-long-day plant with a vernalization requirement. LD or NB during vernalization reduces bolting and flowering, while after vernalization LD promotes them (Pressman and Negbi, 1980). Biennial rosette plants grown under non-inductive conditions will bolt in response to gibberellin application (Lang, 1965). Metzger (1985) found that in the cold-requiring annual field pennycress (Thlaspi arvense L.), stems grew faster and taller when GA3 was applied to non-thermo-induced plants in LD rather than in SD. Similar effects of day length were obtained with other rosette LDP plants pretreated with Amo-1618; i.e. Silene armeria L. (Cleland and Zeevaart, 1970) and spinach (Spinacia oleracea L.) (Zeevaart, 1971) after GA3 treatment and Agrostemma githago (Jones and Zeevaart, 1980) after GA20 treatment. Long photoperiod caused upright presentation of spinach leaves and increased elongation 1 Contribution from the Agricultural Research Organization, The Volcani Centre, Bet Dagan, Israel. No. 1804-E, 1986 series. © Oxford University Press 1987 This content downloaded from 157.55.39.59 on Sat, 15 Oct 2016 04:15:07 UTC All use subject to http://about.jstor.org/terms Pressman and Negbi—Photoperiod and Gibberellin Interactions 969 of the petioles (Zeevaart, 1971). Davis (1967) showed that Proserpinaca palustris L. when maintained on LD grows erect, while in SD it tends to grow prostrate. Wallenstein and Albert (1963) reported that application of GA3 caused P. palustris L. plants grown in SD to grow erect. The leaf number of Arabidopsis thaliana strain ZU was reduced by GA3 or GA7 (Napp-Zinn, 1971). In celery, GA3 caused longer and more erect leaves (Aloni and Pressman, 1980). The present work examined the interaction between photoperiod and applied GAs on bolting and other morphological changes in the three varieties of celery. MATERIALS AND METHODS Plants of leaf celery (Apium graveolens L. var. dulce cv. Florida), an Israeli wild celery (var. lusitanicum) and root celery (var. rapaceum cv. Alabaster) were grown in a glasshouse, in day and night temperatures of 27 °C and 17 °C, respectively, for 70-80 d (up to 8-9 leaves). At this age plants were removed to the phytotron. In the phytotron of the Faculty of Agriculture of the Hebrew University, plants were held in a controlled temperature glasshouse, with day and night temperatures of 27 °C and 22 °C, under natural light. LD (16 h) was obtained by adding incandescent illumination (103 pW cm 2 at plant level) before sunrise and after sunset, and SD (8 h) by transferring the plants to a dark room from 16.00 h to 08.00 h. Night breaks (NB) for plants under the SD conditions, lasted from 23.00 h to 01.00 h. Fluorescent (40 W Tadiran, Israel) cool white tubes provided 200 pW cm-2 at plant level. Gibberellin (in water plus 0 05% Tween 20) was applied directly to the apex using a micropipette in two equal applications 48 h apart. In the first experiment a total of 320 pg was applied per plant. In the second and third experiments 160 pg was applied. In the fourth experiment 80 fig of GA3 or GA4/7 was applied to each plant. RESULTS Stems formed under SD in response to GA3 treatment were almost twice as long as those under LD in the three varieties examined (Table 1). Plants produced a few more leaves under SD than under LD. Application of GA3 reduced the leaf number under the two day length regimes, especially under SD. In Experiment 2 cv. 'Florida' plants maintained under three photoperiods were treated Table 1. The effect of day length on the response to GA3 (320 pg per plant) in celery plants of three varieties. Experiment 1