Role of Abscisic Acid (Aba) and Arabidopsis Thaliana Aba-Insensitive Loci in Low Water Potential-Induced Aba and Proline Accumulation

Journal of Experimental Botany, Vol. 57, No. 1, pp. 201–212, 2006 doi:10.1093/jxb/erj026 Advance Access publication 9 December, 2005

RESEARCH PAPER

Role of abscisic acid (ABA) and Arabidopsis thaliana ABA-insensitive loci in low water potential-induced ABA and proline accumulation

Paul E. Verslues* and Elizabeth A. Bray† Department of Botany and Plant Sciences and Center for Plant Cell Biology, University of California, Riverside, CA 92521, USA

Received 17 June 2005; Accepted 24 October 2005

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Abstract

The mechanisms by which plants respond to reduced water availability (low water potential) include both ABA-dependent and ABA-independent processes. Pro accumulation and osmotic adjustment are two important traits for which the mechanisms of regulation by low water potential, and the involvement of ABA, is not well understood. The ABA-deficient mutant, aba2-1, was used to investigate the regulatory role of ABA in low water potential-induced Pro accumulation and osmotic adjustment in seedlings of Arabidopsis thaliana. Low water potential-induced Pro accumulation required wild-type levels of ABA, as well as a change in ABA sensitivity or ABA-independent events. Osmotic adjustment, in contrast, occurred independently of ABA accumulation in aba2-1. Quantification of low water potential-induced ABA and Pro accumulation in five ABA-insensitive mutants, abi1-1, abi2-1, abi3, abi4, and abi5, revealed that abi4 had increased Pro accumulation at low water potential, but a reduced response to exogenous ABA. Both of these responses were modified by sucrose treatment, indicating that ABI4 has a role in connecting ABA and sugar in regulating Pro accumulation. Of the other abi mutants, only abi1 had reduced Pro accumulation in response to low water potential and ABA application. It was also observed that abi1-1 and abi2-1 had increased ABA accumulation. The involvement of these loci in feedback...