Abstract
On water deficit, abscisic acid (ABA) induces stomata closure to reduce water loss by transpiration. To identify Arabidopsis thaliana mutants which transpire less on drought, infrared thermal imaging of leaf temperature has been used to screen for suppressors of an ABA-deficient mutant (aba3-1) cold-leaf phenotype. Three novel mutants, called hot ABA-deficiency suppressor (has), have been identified with hot-leaf phenotypes in the absence of the aba3 mutation. The defective genes imparted no apparent modification to ABA production on water deficit, were inherited recessively and enhanced ABA responses indicating that the proteins encoded are negative regulators of ABA signalling. All three mutants showed ABA-hypersensitive stomata closure and inhibition of root elongation with little modification of growth and development in non-stressed conditions. The has2 mutant also exhibited increased germination inhibition by ABA, while ABA-inducible gene expression was not modified on dehydration, indicating the mutated gene affects early ABA-signalling responses that do not modify transcript levels. In contrast, weak ABA-hypersensitivity relative to mutant developmental phenotypes suggests that HAS3 regulates drought responses by both ABA-dependent and independent pathways. has1 mutant phenotypes were only apparent on stress or ABA treatments, and included reduced water loss on rapid dehydration. The HAS1 locus thus has the required characteristics for a targeted approach to improving resistance to water deficit. In contrast to has2, has1 exhibited only minor changes in susceptibility to Dickeya dadantii despite similar ABA-hypersensitivity, indicating that crosstalk between ABA responses to this pathogen and drought stress can occur through more than one point in the signalling pathway.
Highlights
Environmental abiotic stresses, such as drought, high salinity and cold, have a major effect on plant development and yield
Seedlings from M2 pools were screened by infrared thermography for suppression of the cold leaf phenotype observed in the original aba3-1 mutant
This paper describes the isolation of three new mutants affected in stomata responses to abscisic acid (ABA) using a novel screen for suppression of the cold leaf phenotype exhibited by the ABA-deficient mutant aba3-1
Summary
Environmental abiotic stresses, such as drought, high salinity and cold, have a major effect on plant development and yield. Despite its reputation as a stress hormone, ABA is involved in the control of other physiological processes. It participates in plant vegetative development in a concentration-dependent manner, stimulating growth at low concentrations and inhibiting growth at high concentrations [2,3]. It is essential for seed development: during maturation it promotes the acquisition of reserves and desiccation tolerance and induces dormancy by inhibiting germination [4]
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