مقاله انگلیسی رایگان در مورد تقویت تحمل نیشکر در خشکی – الزویر 2018

Plants close stomata to avoid losing water through transpiration under water limiting conditions (Chaves, 1991), a physiological response that is related to either hydraulic or chemical signals (Davies and Zhang, 1991; Christmann et al., 2007). Plant acclimation to water deficits involves morphological changes that regulate water balance, with plants showing decreases in leaf area and shoot/root ratio (Pimentel, 2004). Cell osmoregulation by solutes such as sugars, glycine-betaine, and proline is another response to water deficits, allowing the maintenance of water content and protecting cellular structures (Verlues et al., 2006). Rapid stomatal response to changes in water availability is an important feature in sugarcane (Saccharum spp.), preventing excessive loss of leaf turgor and further decreases in leaf water content (Ribeiro et al., 2013). However, it is well-known that stomatal closure causes low CO2 availability for photosynthetic enzymes (Du et al., 1996; Chaves et al., 2009; Machado et al., 2013) and then an imbalance between photochemical and biochemical reactions in the leaves. Therefore, production of reactive oxygen species (ROS) is enhanced under drought conditions, and plants should be able to control such deleterious molecules through their antioxidant system. This protective system consists of several enzymatic and non-enzymatic compounds, which prevent oxidative damage by scavenging ROS inside cells (Mittler, 2002). For instance, increases in superoxide dismutase and ascorbate peroxidase activities were associated with rapid recovery of leaf gas exchange in sugarcane plants after rehydration (Sales et al., 2013). These reported plant responses to a single drought event are quite common; however, plants are exposed to recurrent cycles of drought and rehydration in nature, and the consequences of such repetitive drought events are less understood (Walter et al., 2011). Plants can acclimate to varying water conditions through morphological and physiological changes, which favor the maintenance of plant growth or survival under stressful conditions (Chaves et al., 2002). Some changes during an acclimation period can allow faster responses and enhanced plant performances during the next stressful event. In fact, an experimental design with repeated cycles of droughts is a more realistic approach when considering plants in their natural environment, with improved plant performances under limiting conditions being found in several species when there was previous exposure to stressful conditions. While Trifolium alexandrinum was able to maintain high leaf water potential and relative water content after a second drought event (Iannucci et al., 2000), Quercus ilex exhibited reductions in leaf water potential and transpiration accompanied by osmotic adjustment after hardening (Villar-Salvador et al., 2004). Seedlings of Moringa oleifera that had previously been subjected to osmotic stress experienced increased drought tolerance, with plants showing higher water-use efficiency, higher photosynthesis and increases in activity of antioxidant enzymes under water deficit conditions (Rivas et al., 2013). However, most of these studies compared plants of differing ages under varying stress intensities and environmental conditions, which makes the study of stress memory difficult.