JXB Advance Access originally published online on June 23, 2006
Journal of Experimental Botany 2006 57(10):2421-2434; doi:10.1093/jxb/erj215
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© 2006 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 |
Field studies on the regulation of abscisic acid content and germinability during grain development of barley: molecular and chemical analysis of pre-harvest sprouting

1Department of Wheat and Barley Research, National Institute of Crop Science, National Agriculture and Bio-oriented Research Organization, 2-1-18 Kannondai, Tsukuba, Ibaraki 305-8518, Japan
2Department of Physiology and Quality Science, National Institute of Vegetable and Tea Science, National Agriculture and Bio-oriented Research Organization, 360 Kusawa, Ano, Mie 514-2392, Japan
3Plant Science Center, RIKEN, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan
4Department of Life Science, Faculty of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan
*To whom correspondence should be addressed. E-mail: mchono{at}affrc.go.jp
To investigate whether the regulation of abscisic acid (ABA) content was related to germinability during grain development, two cDNAs for 9-cis-epoxycarotenoid dioxygenase (HvNCED1 and HvNCED2) and one cDNA for ABA 8'-hydroxylase (HvCYP707A1), which are enzymes thought to catalyse key regulatory steps in ABA biosynthesis and catabolism, respectively, were cloned from barley (Hordeum vulgare L.). Expression and ABA-quantification analysis in embryo revealed that HvNCED2 is responsible for a significant increase in ABA levels during the early to middle stages of grain development, and HvCYP707A1 is responsible for a rapid decrease in ABA level thereafter. The change in the embryonic ABA content of imbibing grains following dormancy release is likely to reflect changes in the expression patterns of HvNCEDs and HvCYP707A1. A major change between dormant and after-ripened grains occurred in HvCYP707A1; the increased expression of HvCYP707A1 in response to imbibition, followed by a rapid ABA decrease and a high germination percentage, was observed in the after-ripened grains, but not in the dormant grains. Under field conditions, HvNCED2 showed the same expression level and pattern during grain development in 2002, 2003, and 2004, indicating that HvNCED2 expression is regulated in a growth-dependent manner in the grains. By contrast, HvNCED1 and HvCYP707A1 showed a different expression pattern in each year, indicating that the expression of these genes is affected by environmental conditions during grain development. The varied expression levels of these genes during grain development and imbibition, which would have effects on the activity of ABA biosynthesis and catabolism, might be reflected, in part, in the germinability in field-grown barley.
Key words: ABA 8'-hydroxylase, abscisic acid, dormancy, field-grown barley, germination, nine-cis-epoxycarotenoid dioxygenase, pre-harvest sprouting
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