Abstract
Heat and drought stress have emerged as major constraints for durum wheat production. In the Mediterranean area, their negative effect on crop productivity is expected to be exacerbated by the occurring climate change. Xyloglucan endotransglucosylase/hydrolases (XTHs) are chief enzymes in cell wall remodeling, whose relevance in cell expansion and morphogenesis suggests a central role in stress responses. In this work the potential role of XTHs in abiotic stress tolerance was investigated in durum wheat. The separate effects of dehydration and heat exposure on XTH expression and its endotransglucosylase (XET) in vitro activity and in vivo action have been monitored, up to 24 h, in the apical and sub-apical root regions and shoots excised from 3-day-old seedlings of durum wheat cultivars differing in stress susceptibility/tolerance. Dehydration and heat stress differentially influence the XTH expression profiles and the activity and action of XET in the wheat seedlings, depending on the degree of susceptibility/tolerance of the cultivars, the organ, the topological region of the root and, within the root, on the gradient of cell differentiation. The root apical region was the zone mainly affected by both treatments in all assayed cultivars, while no change in XET activity was observed at shoot level, irrespective of susceptibility/tolerance, confirming the pivotal role of the root in stress perception, signaling, and response. Conflicting effects were observed depending on stress type: dehydration evoked an overall increase, at least in the apical region of the root, of XET activity and action, while a significant inhibition was caused by heat treatment in most cultivars. The data suggest that differential changes in XET action in defined portions of the root of young durum wheat seedlings may have a role as a response to drought and heat stress, thus contributing to seedling survival and crop establishment. A thorough understanding of the mechanisms underlying these variations could represent the theoretical basis for implementing breeding strategies to develop new highly productive hybrids adapted to future climate scenarios.
Highlights
The extraordinary acceleration of human population growth in recent centuries is determining a fast-increasing demand for food, mainly cereals, and other agronomic crops
In the Mediterranean area these two stresses usually occur simultaneously, this study reports the separate effects of dehydration and heat exposure on Xyloglucan endotransglucosylase/hydrolases (XTHs) expression as well as XTH expression and its endotransglucosylase (XET) in vitro activity and in vivo action in apical and sub-apical root regions and shoots excised from 3-day-old seedlings of durum wheat (T. durum Desf.) cultivars (Svevo, Creso, Ardente, and Simeto) differing in stress susceptibility/tolerance
Our results indicate that dehydration and heat stress, applied singularly, differentially influence the XTH expression profiles and the activity and action of XET in wheat seedlings, depending on the degree of susceptibility/tolerance of the cultivars
Summary
The extraordinary acceleration of human population growth in recent centuries is determining a fast-increasing demand for food, mainly cereals, and other agronomic crops. Modern farming techniques and plant breeding programs enabled a linear enhancement in agricultural productivity; the positive trend is expected to slow down because global climate change is leading to adverse environmental conditions and to related negative effects on crop quality and yield (Lobell and Gourdji, 2012). Dramatic changes in rainfall frequency, intensity, duration, and distribution have been forecast at regional scale (Kao and Ganguly, 2011). This combination of events could significantly modify the levels of heat and drought stresses negatively impacting growth, development, and productivity of cultivated plants (Trenberth, 2011; Vadez et al, 2011). For example, a decrease of the kernel number inside the ear (Sekhon et al, 2010), of the number and size of starch granules and of the amount of lipids and proteins within the kernel (Wilhelm et al, 1999) has been reported under stress conditions, besides significant variations in the bromatological composition of flours (Wardlaw et al, 2002; Balla et al, 2011)
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