Abstract
Abiotic stresses reduce crop growth and yield in part by disrupting metabolic homeostasis and triggering responses that change the metabolome. Experiments designed to understand the mechanisms underlying these metabolomic responses have usually not used agriculturally relevant stress regimes. We therefore subjected maize plants to drought, salt, or heat stresses that mimic field conditions and analyzed leaf responses at metabolome and transcriptome levels. Shared features of stress metabolomes included synthesis of raffinose, a compatible solute implicated in tolerance to dehydration. In addition, a marked accumulation of amino acids including proline, arginine, and γ-aminobutyrate combined with depletion of key glycolysis and tricarboxylic acid cycle intermediates indicated a shift in balance of carbon and nitrogen metabolism in stressed leaves. Involvement of the γ-aminobutyrate shunt in this process is consistent with its previously proposed role as a workaround for stress-induced thiamin-deficiency. Although convergent metabolome shifts were correlated with gene expression changes in affected pathways, patterns of differential gene regulation induced by the three stresses indicated distinct signaling mechanisms highlighting the plasticity of plant metabolic responses to abiotic stress.
Highlights
Important abiotic stresses for crop plants include heat, drought, and salinity
To quantify effects of realistic stress environments on metabolic homeostasis of maize leaves, we analyzed leaf metabolomes of B73 inbred plants grown under long-term, non-lethal heat, drought, or salt stress treatments
As detailed in Materials and Methods, drought stress imposed by withholding water intensified gradually over a two-week period to mimic a natural stress environment
Summary
Important abiotic stresses for crop plants include heat, drought, and salinity (salt). These stresses are expected to become increasingly prevalent worldwide due to climate change [1]. Photosynthesizing leaves are sensitive to these stresses because the capacity for uptake of CO2 through leaf stomatal pores must be balanced against the rate of water loss via transpiration. Transpiration contributes to leaf cooling provided that transport of water from the roots can be maintained, whereas under drought stress, transpiration and gas exchange are curtailed by stomatal closure to prevent dehydration [2,3]. While heat, drought, and salt stresses have distinct impacts on photosynthetic metabolism, they overlap and interact in important ways [5,6]. All include a likelihood that leaf cells of stressed plants will experience lowered water potentials
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