Abstract
Drought tolerance in barley is highly correlated with the expression of two genes: Hordeum vulgare aleurone 1 (HVA1) and stress-responsive gene 6 (SRG6). Though their role in the mechanism of drought response in barley has been confirmed in transgenic plants, the regulation pathways of these genes’ expression have not been sufficiently studied, especially on the level of whole plants. We used four barley genotypes of different drought tolerance to establish and compare the expression profiles of SRG6 and HVA1 and to associate them with the possible physiological and biochemical signals of water deficit. Both genes studied were expressed to a greater extent in drought tolerant genotypes. The highest level of HVA1 transcript accumulation was observed under conditions where the leaf water potential decreased significantly. In tolerant genotype this signal was partially replaced with abscisic acid (ABA) signal of soil water deficit and the final transcript accumulation was about 14 times lower than in the case of leaf water deficit. In the case of SRG6 the main signal which can triggered the transcript accumulation was ABA but in the case of tolerant genotype the direct effect of leaf water deficit was also observed. Thus, it seems to be possible that in drought tolerant barley genotypes, HVA1 and SRG6, are not only more expressed during drought, but tolerant genotypes may be also more sensitive to various internal signals confirming environmental water deficit. The putative role of hydrogen peroxide as a signal of water deficit in the regulation of both genes expression was not confirmed. The drought-induced expression of both HVA1 and SRG6 was additionally reduced in the light. Because of this powerful complexity, a true understanding of plant response to drought requires further studies integrating gene expression and cell signaling analysis in single organs or tissues with whole plant physiology and long distance signaling.
Highlights
Crop productivity, including that of two-row barley (Hordeum distichon), is lower in most cases than the yielding potential determined by the climate and soil conditions of the cultivated area
We assumed that because the position of these genes in the chain of reactions of the drought response is quite different, stress-responsive gene 6 (SRG6) being probably a transcription factor and, taking part in the primary response and Hordeum vulgare aleurone 1 (HVA1) encoding a protective protein and as such situated in the end of this chain, the factors triggering their expression would not be the same
In plants growing under conditions of elevated transpiration rate, which contain more abscisic acid (ABA) but the same amount of water in comparison to the leaves of the same age in plants growing at normal transpiration level, the higher accumulation of SRG6 transcript was observed
Summary
Crop productivity, including that of two-row barley (Hordeum distichon), is lower in most cases than the yielding potential determined by the climate and soil conditions of the cultivated area. Drought tolerance is under complex genetic control, and many genes are involved in plant response to water deficit (Tuberosa and Salvi 2006; Cattivelli et al 2008). The expression of these genes is controlled by various cellular signals, and the exact function of different signaling pathways is still unclear. An effort is being made to recognize signals of decreased turgor pressure and water loss in single cells (Boudsocq and Lauriere 2005) Such signals directly trigger gene expression and induct the biosynthesis of abscisic acid (ABA), which may partially regulate different sets of the genes. At the whole plant level, the drought response is much more complicated
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