دانلود رایگان مقاله انگلیسی تقویت تحمل نیشکر درخشکی با قرار گرفتن در معرض کمبود آب در گذشته - الزویر 2018

ABSTRACT

Under field conditions, plants are exposed to cycles of dehydration and rehydration during their lifespan. In this study, we hypothesized that sugarcane plants previously exposed to cycles of water deficits will perform better than plants that have never faced water deficits when both are subjected to low water availability. Sugarcane plants were grown in a nutrient solution and exposed to one (1WD), two (2WD) or three (3WD) water deficit cycles. As the reference, plants were grown in a nutrient solution without adding polyethylene glycol. Under water deficits, leaf gas exchange was significantly reduced in 1WD and 2WD plants. However, 3WD plants showed similar CO2 assimilation and lower stomatal conductance compared to the reference plants, with increases in intrinsic water-use efficiency. Abscisic acid concentrations were lower in 3WD plants than in 1WD plants. Our data revealed root H2O2 concentration as an important chemical signal, with the highest root H2O2 concentrations found in 3WD plants. These plants presented higher root dry matter and root:shoot ratios compared to the reference plants, as well as higher biomass production when water was available. Our data suggest that sugarcane plants were able to store information from previous stressful events, with plant performance improving under water deficits. In addition, our findings provide a new perspective for increasing drought tolerance in sugarcane plants under nursery conditions.

4. Discussion

4.1. Sugarcane photosynthesis is benefited by repetitive cycles of drought/ rehydration

Photosynthetic rates of plants exposed to three water deficit cycles were similar to the rates found in the reference plants (Fig. 1A), and the rates were even higher when considering the integrated CO2 gain during the experimental period (Fig. S3A). In fact, a better performance was the result of higher photosynthetic rates during the recovery period (Fig. 2A). Under water deficit, both photosynthesis and stomatal conductance of plants exposed to three water deficit cycles were higher than that found in plants subjected to one or two water deficit cycles (Fig. 1A, B), suggesting that stomatal aperture was one factor leading to the better photosynthetic performance of 3WD plants under low water availability.

The higher stomatal conductance of 3WD plants was associated with increases in root biomass (Fig. 7B), which likely improved water uptake from the nutrient solution. In addition, 3WD plants had higher root to shoot ratios (Fig. 7C), indicating changes in carbon partitioning and investment in root structure. Besides these morphological changes that support a higher stomatal aperture, our data suggest that ABA has a role in stomatal conductance of sugarcane plants under water deficit. We noticed that 3WD plants had lower leaf ABA concentrations than 1WD plants (Fig. 4A), as well as a lower amount of DPA, a product of ABA oxidation (Fig. 4D). Thus, we can argue that the amount of DPA was higher in 1WD plants due to a large amount of ABA being produced and oxidized (Fig. 4). Based on Virlouvet and Fromm (2015), plants previously exposed to drought have low stomatal conductance caused by ABA biosynthesis. Such associations between ABA and stomatal conductance were found in this study, with the lowest gs values found in plants with the highest concentrations of ABA and its derivatives (Fig. 4). Interestingly, sugarcane plants subjected to three water deficit cycles did not present such high levels of ABA and DPA, which are a likely consequence of better hydration and/or changes in ABA metabolism caused by repetitive cycles of water deficits.