Physiological and Molecular Osmotic Stress Responses in Three Durum Wheat (Triticum Turgidum ssp Durum) Genotypes

Abstract

This study aims to investigate the activities and expression of enzymes of primary metabolism and relate these data with the growth performance of three different durum wheat genotypes (Maali; YT13; and ON66) under osmotic stress. Growth traits-including plant height, dry weight (DW) and relative water content (RWC)-were measured to classify genotypes depending on their tolerance to stress. Several enzymes were investigated: Ascorbate peroxidase (APX), Glutamine Synthetase (GS), Glutamine dehydrogenase (GDH), Glutamate synthase (GOGAT), Glucose 6-phosphate dehydrogenase (G6PDH), and Phosphoenolpyruvate Carboxylase (PEPC). The expression of the cytosolic and plastidic glutamine synthetase (TaGS1 and TaGS2), high affinity nitrate transporters (TaNRT2.3) and Glutamate dehydrogenase (TaGDH) were also detected by qRT-PCR. The results indicated different growth performances among genotypes, indicating Maali and YT13 as tolerant genotypes and ON66 as a drought-susceptible variety. Data showed a decrease in PEPC and increase in APX activities under osmotic stress; a slight decrease in GS activity was observed, together with an increase in G6PDH in all genotypes; GS and NRT2 expressions changed in a similar pattern in the different genotypes. Interestingly, Maali and YT13 showed higher transcript abundance for GDH under stress compared to ON66, suggesting the implication of GDH in protective phenomena upon osmotic stress.Agronomy 2019, 9, 550 2 of 15 the photosynthetic activity by its direct effect on CO 2 uptake, resulting in a significant reduction in biomass and shoot growth [2][3][4]. At the cellular level, water scarcity triggers a set of modifications in biological processes caused by modifications in gene expression [5]. An integrated comprehension of morphological and physiological responses to drought requires a deep knowledge of both biochemical and molecular diversity among different genotypes. Indeed, distinct behaviors were observed in susceptible and tolerant genotypes resulting in changes in biomass production, plant height, and greenness [3,6]; these variations are consequences of many visible responses, such as osmolytes syntheses, enzymatic activities, antioxidant machinery, and specific gene expression [3,[7][8][9].In response to water limitation, plants tend to reduce damages by maintaining an optimum water status; to this aim, a set of compatible solutes are synthesized, namely water-soluble carbohydrates (WSC). These components help cells to maintain their turgor. In this context, it has been shown that tolerant genotypes accumulated more WSC than drought-susceptible ones [10].Water scarcity affects different enzymatic activities; among them, the nitrogen metabolism machinery plays a pivotal role in nitrogen utilization [3,8,11]. The activity of the enzymes involved in the GS-GOGAT cycle, a key pathway in nitrogen remobilization, was shown to be widely affected by water stress. Glutamine synthetase (GS), with its two isoforms (cytosolic GS1, and plastidic GS2), is a potential indicator of plant nutri...

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