Abstract
Inhibition of leaf elongation and expansion is one of the earliest responses of rice to water deficit. Despite this sensitivity, a great deal of genetic variation exists in the extant of leaf elongation rate (LER) reduction in response to declining soil moisture. We analyzed global gene expression in the leaf elongation zone under drought in two rice cultivars with disparate LER sensitivities to water stress. We found little overlap in gene regulation between the two varieties under moderate drought; however, the transcriptional response to severe drought was more conserved. In response to moderate drought, we found several genes related to secondary cell wall deposition that were down regulated in Moroberekan, an LER tolerant variety, but up-regulated in LER sensitive variety IR64.
Highlights
The inhibition of leaf expansion under drought is an important adaptive mechanism to limit leaf area and transpirative loss while water is scarce
Our results indicate that genotypic differentiation of leaf elongation rates is greater under moderate drought stress, whereas under severe stress elongation rates decline sharply in both genotypes
This result indicates that genotypic comparisons of growth response dynamics to water deficit are more relevant under mild stress than under severe drought, when most of the cellular and metabolic processes are affected and the plant reaches drought survival phase [7]
Summary
The inhibition of leaf expansion under drought is an important adaptive mechanism to limit leaf area and transpirative loss while water is scarce. Leaf elongation rate (LER) is one of the first physiological parameters to respond to decreasing soil moisture; a reduction in LER precedes changes in transpiration and leaf water potential [1]. Compared with maize or soybean, LER in rice is especially sensitive to drying soil [2]. Reducing LER can be an important adaptive mechanism for dehydration tolerance, in crop production systems the loss of leaf area during canopy establishment can be disadvantageous for yield, in rain-fed rice ecosystems prone to episodic vegetative drought [3]. Despite the sensitivity of rice to drought, some varieties maintain leaf water potential under water deficit through the regulation of stomatal closure. Though a proportion of the genotypic differences in leaf elongation in rice can be attributed to root variability, significant differences in the response of leaf elongation to drought exist even after rooting effects are neutralized [4]
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