Abstract
Main conclusionsSugar-mediated osmotic acclimation and a strong antioxidative response reduce drought-induced biomass loss at the vegetative stage in rice.A clear understanding of the physiological and biochemical adaptations to water limitation in upland and aerobic rice can help to identify the mechanisms underlying their tolerance to low water availability. In this study, three indica rice varieties-IR64 (lowland), Apo (aerobic), and UPL Ri-7 (upland)-, that are characterized by contrasting levels of drought tolerance, were exposed to drought at the vegetative stage. Drought-induced changes in biomass, leaf metabolites and oxidative stress markers/enzyme activities were analyzed in each variety at multiple time points. The two drought-tolerant varieties, Apo and UPL Ri-7 displayed a reduced water use in contrast to the susceptible variety IR64 that displayed high water consumption and consequent strong leaf dehydration upon drought treatment. A sugar-mediated osmotic acclimation in UPL Ri-7 and a strong antioxidative response in Apo were both effective in limiting the drought-induced biomass loss in these two varieties, while biomass loss was high in IR64, also after recovery. A qualitative comparison of these results with the ones of a similar experiment conducted in the field at the reproductive stage showed that only Apo, which also in this stage showed the highest antioxidant power, was able to maintain a stable grain yield under stress. Our results show that different metabolic and antioxidant adaptations confer drought tolerance to aerobic and upland rice varieties in the vegetative stage. The effectiveness of these adaptations differs between developmental stages. Unraveling the genetic control of these mechanisms might be exploited in breeding for new rice varieties adapted to water-limited environments.
Highlights
In the coming decades, drought episodes associated with global climate change are projected to become more frequent and erratic
In this context, improving drought tolerance in rice will be critical to meet the growing global food demand, considering that, in Asia, ~ 40% of the total crop area is cultivated in rainfed agroecosystems (FAO 2014) which are prone to droughts
In IR64, non-structural carbohydrates stored in the stem might have been remobilized to stabilize leaf growth and provide osmotic protection under drought already at the vegetative stage
Summary
Drought episodes associated with global climate change are projected to become more frequent and erratic. Previous research on drought, has shown that accumulation of particular metabolites in leaves (e.g., raffinose, trehalose, proline, and glycine betaine) can have a protective function whereas the accumulation of other metabolites may be a consequence of drought (for example the increase in free amino acids from protein breakdown) (Verslues and Juenger 2011; Krasensky and Jonak 2012; Obata and Fernie 2012; Fàbregas and Fernie 2019) Another effect of drought-induced stomatal closure and lower carbon availability, is an enhanced generation of reactive oxygen species (ROS) (Suzuki et al 2012; Noctor et al 2014) responsible for oxidative damage that drives the cell into senescence (Halliwell 2006) and, in extreme cases, death (Van Breusegem and Dat 2006). A complex enzymatic and non-enzymatic antioxidative system protects plants against this oxidative damage, and is essential for conferring drought tolerance (Mittler et al 2011; Baxter et al 2014; You and Chan 2015; Soares et al 2019)
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