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JXB Advance Access originally published online on September 17, 2008
Journal of Experimental Botany 2008 59(13):3729-3739; doi:10.1093/jxb/ern224
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

CsPLD{alpha}1 and CsPLD{gamma}1 are differentially induced during leaf and fruit abscission and diurnally regulated in Citrus sinensis

Anish Malladi * and Jacqueline K. Burns{dagger}

University of Florida/IFAS, Horticultural Sciences Department, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850, USA

{dagger} To whom correspondence should be addressed: E-mail: jkbu{at}ufl.edu

Understanding leaf and fruit abscission is essential in order to develop strategies for controlling the process in fruit crops. Mechanisms involved in signalling leaf and fruit abscission upon induction by abscission agents were investigated in Citrus sinensis cv. ‘Valencia’. Previous studies have suggested a role for phospholipid signalling; hence, two phospholipase D cDNA sequences, CsPLD{alpha}1 and CsPLD{gamma}1, were isolated and their role was examined. CsPLD{alpha}1 expression was reduced in leaves but unaltered in fruit peel tissue treated with an ethylene-releasing compound (ethephon), or a fruit-specific abscission agent, 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP). By contrast, CsPLD{gamma}1 expression was up-regulated within 6 h (leaves) and 24 h (fruit peel) after treatment with ethephon or CMNP, respectively. CsPLD{alpha}1 expression was diurnally regulated in leaf blade but not fruit peel. CsPLD{gamma}1 exhibited strong diurnal oscillation in expression in leaves and fruit peel with peak expression around midday. While diurnal fluctuation in CsPLD{alpha}1 expression appeared to be light-entrained in leaves, CsPLD{gamma}1 expression was regulated by light and the circadian clock. The diurnal expression of both genes was modulated by ethylene-signalling. The ethephon-induced leaf abscission and the ethephon- and CMNP-induced decrease in fruit detachment force were enhanced by application during rising diurnal expression of CsPLD{gamma}1. The results indicate differential regulation of CsPLD{alpha}1 and CsPLD{gamma}1 in leaves and fruit, and suggest possible roles for PLD-dependent signalling in regulating abscission responses in citrus.

Key words: Abscission, circadian, Citrus sinensis, diurnal, ethephon, phospholipase D

* Present address: 1121 Miller Plant Sciences Building, Department of Horticulture, University of Georgia, Athens, GA 30602, USA.

Received 5 June 2008; Revised 26 July 2008 Accepted 4 August 2008


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