Abstract
Understanding how plants tolerate dehydration is a prerequisite for developing novel strategies for improving drought tolerance. The desiccation-tolerant (DT) Sporobolus stapfianus and the desiccation-sensitive (DS) Sporobolus pyramidalis formed a sister group contrast to reveal adaptive metabolic responses to dehydration using untargeted global metabolomic analysis. Young leaves from both grasses at full hydration or at 60% relative water content (RWC) and from S. stapfianus at lower RWCs were analyzed using liquid and gas chromatography linked to mass spectrometry or tandem mass spectrometry. Comparison of the two species in the fully hydrated state revealed intrinsic differences between the two metabolomes. S. stapfianus had higher concentrations of osmolytes, lower concentrations of metabolites associated with energy metabolism, and higher concentrations of nitrogen metabolites, suggesting that it is primed metabolically for dehydration stress. Further reduction of the leaf RWC to 60% instigated a metabolic shift in S. stapfianus toward the production of protective compounds, whereas S. pyramidalis responded differently. The metabolomes of S. stapfianus leaves below 40% RWC were strongly directed toward antioxidant production, nitrogen remobilization, ammonia detoxification, and soluble sugar production. Collectively, the metabolic profiles obtained uncovered a cascade of biochemical regulation strategies critical to the survival of S. stapfianus under desiccation.
Highlights
The impact of drought on crop production is of continuous and growing concern as the world struggles to meet food production targets for an increasing global population
The leaves of S. stapfianus curl as dehydration progresses after the cessation of irrigation, and, under our conditions, appear to curl to particular degrees at specific relative water content (RWC); leaves are halfway curled at 68% RWC and fully curled at 44% RWC, as described previously (Gaff et al, 2009)
Our results show clearly that nitrogen metabolism and protection from oxidative stress are tightly linked in S. stapfianus as it dries beyond 40% RWC (Figure 9)
Summary
The impact of drought on crop production is of continuous and growing concern as the world struggles to meet food production targets for an increasing global population. Cellular responses to water deficits include growth inhibition, stomatal closure, limited transpiration, and reduced photosynthesis, and those responses that enhance cellular dehydration tolerance (Mullet and Whitsitt, 1996). Most studies of water deficit responses in plants do not attempt to reach water potentials that would generate significant cellular dehydration, and many remain in the range where osmotic adjustment can prevent significant dehydration of the cellular environment. This is because most present-day angiosperms cannot survive dehydration of their vegetative tissues to 20 to 30% of full turgor (RWC), which translates to between 25 and 210 MPa (Proctor and Pence, 2002). Despite the array of data characterizing water deficit responses that may relate to dehydration tolerance, there is still little understanding as to which responses, whether at the gene or cellular level, are adaptive in nature and truly critical for or central to tolerance (Bray, 2002)
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