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AOBPreview originally published online on June 25, 2007
Annals of Botany 2008 101(2):249-259; doi:10.1093/aob/mcm115
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© The Author 2007. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Differential Effects of NAA and 2,4-D in Reducing Floret Abscission in Cestrum (Cestrum elegans) Cut Flowers are Associated with their Differential Activation of Aux/IAA Homologous Genes

Bekele Abebie1,2, Amnon Lers2, Sonia Philosoph-Hadas2, Raphael Goren1,*, Joseph Riov1 and Shimon Meir2

1 The Kennedy-Leigh Centre for Horticultural Research, The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100, Israel
2 Department of Postharvest Science of Fresh Produce, The Volcani Center, Agricultural Research Organization, Bet-Dagan, 50250, Israel

* For correspondence. E-mail Rgoren{at}agri.huji.ac.il

Received: 14 February 2007    Returned for revision: 20 March 2007    Accepted: 14 April 2007    Published electronically: 25 June 2007

Background and Aims: A previous study showed that the relative effectiveness of 2,4-dichlorophenoxyacetic acid (2,4-D) compared with that of 1-naphthaleneacetic acid (NAA) in reducing floret bud abscission in cestrum (Cestrum elegans) cut flowers was due to its acropetal transport. The aim of the present study was to examine if the differential effect of these auxins on floret abscission is reflected in the expression of Aux/IAA genes in the floret abscission zone (AZ).

Methods: cDNAs were isolated by PCR-based cloning from the floret AZ of auxin-treated cut flowers. The expression patterns of the cDNAs in various tissues and the effect of indole-3-acetic acid (IAA), applied with or without cycloheximide, on their expression in the floret AZ were examined by northern blot analysis. The regulation of transcript accumulation in the floret AZ in response to NAA or 2,4-D was measured by real-time PCR during auxin pulsing of cut flowers and vase life, concomitantly with floret abscission.

Key Results: Six isolated cDNAs were identified to represent Aux/IAA homologous genes, designated as Cestrum elegans (Ce)-IAA1 to Ce-IAA6. Four Ce-IAA genes were characterized as early auxin-responsive genes (ARGs), and two (Ce-IAA1 and Ce-IAA5) as late ARGs. Only Ce-IAA5 was AZ-specific in floret buds. A temporal regulation of Ce-IAA transcript levels in the floret AZ was found, with 2,4-D inducing higher expression levels than NAA in floret buds. These Ce-IAA expression levels were negatively correlated with floret abscission.

Conclusions: The differential transport characteristics of NAA and 2,4-D in cestrum cut flowers were reflected in differential activation of the Ce-IAA genes identified in the floret AZ. Therefore, Aux/IAA genes can be used as molecular markers to measure auxin activity, which reflects free auxin level in the AZ. Two of the identified genes, Ce-IAA1 and Ce-IAA5, may also have a regulatory role in abscission.

Key words: Abscission zone, auxin, Aux/IAA gene expression, Cestrum elegans, cut flowers, cycloheximide, 2,4-D, floret abscission, NAA


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