Theobroxide inhibits stem elongation in Pharbitis nil by regulating jasmonic acid and gibberellin biosynthesis Fanjiang Kong, Xiquan Gao, Kyong-Hee Nam, Kosaku Takahashi, Hideyuki Matsuura, Teruhiko Yoshihara * Graduate School of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo 060-8589, Japan Received 25 February 2005; received in revised form 17 May 2005; accepted 18 May 2005 Available online 9 June 2005 Abstract In this study, exogenous factors affecting the elongation growth in the short day plant, Pharbitis nil, was investigated. Theobroxide inhibited stem elongation in P. nil both under short day (SD) and long day (LD) conditions. Salicylhydroxamic acid (SHAM), an inhibitor of jasmonic acid (JA) biosynthesis, and GA 3 recovered the inhibitory effect of theobroxide on stem elongation. Quantitative analysis of JA showed that the level of endogenous JA increased significantly in theobroxide treated plants, while exogenously applied GA 3 and SHAM suppressed JA biosynthesis stimulated by theobroxide. The activity of lipoxygenase (LOX, the key enzyme of JA biosynthesis) also was stimulated by theobroxide and this stimulation was nullified by SHAM and GA 3 . Quantitative analysis of GA 1 showed that theobroxide suppressed GA 1 biosynthesis. In non theobroxide treated P. nil, SD conditions stimulated JA biosynthesis and LOX activity, while GA 1 biosynthesis was suppressed. All these results suggest that JA probably is involved negatively in the control of stem elongation, and the balance between JA and gibberellin might determine the stem growth in P. nil. # 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Theobroxide; Jasmonic acid; Gibberellin; Stem elongation; Lipoxygenase; Pharbitis nil 1. Introduction Theobroxide, a potato tuber inducing compound, was isolated from the culture filtrate of Lasiodiplodia theobro- mae [1]. Interestingly, spraying theobroxide on the leaflets of potatoes (Solanum tuberosum L.) and the leaves of morning glories (Pharbitis nil), induced formation of potato tuber and flower buds, respectively, under non-inductive conditions [2]. Another report showed that theobroxide-induced potato tuber formation was correlated with increased endogenous levels of JA, and elevated LOX activity [3]. Moreover, the inductive effect of theobroxide on potato tuber formation was eliminated by applying SHAM, which was a JA biosynthesis inhibitor [4]. Many recent studies have demonstrated that JA is a significant component of the signaling pathway that regulates the expression of plant defense genes in response to various environmental stresses [5]. Other fundamental and remarkable roles of the jasmonates include their regulation of plant morphogenesis [5]. Needless to say, plant morphogenesis is controlled mainly by the frequency and direction of cell division, and the direction of cell expansion. The production of organs or tissues with defined shapes must be precisely controlled among the constituent cells. JA and JA-Me are known to participate in the control of the elongation growth of plants [6]. In dwarf rice seedlings, exogenous JA reduces the effect of GA 3 on the elongation of the second leaf sheath [7]. In lettuce, applied JA also diminishes the effect of GA 3 on the elongation of hypocotyls [7]. Exogenously applied JA substantially inhibits IAA-induced elongation of etiolated oat coleoptile segments [8]. In soybean, endogenous JA is involved in the control of the stem growth habit [9]. Exogenous JA-Me inhibits roots and shoots growth in P. nil [10]. www.elsevier.com/locate/plantsci Plant Science 169 (2005) 721–725 Abbreviations: GC–SIM-MS, gas chromatography–selected ion mon- itoring-mass spectrometry; GA, gibberellin; Jasmonates, JA and its related compounds; JA, jasmonic acid; LD, long day; LOX, lipoxygenase; JA-Me, methyl jasmonate; SHAM, salicylhydroxamic acid; SD, short day * Corresponding author. Tel.: +81 11 706 2505; fax: +81 11 706 2505. E-mail address: yosihara@chem.agr.hokudai.ac.jp (T. Yoshihara). 0168-9452/$ – see front matter # 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2005.05.023