Metabolomic approaches highlight two mechanisms of accelerated grain filling in Mediterranean oat (Avena sativa L.) cultivars during drought.

Grain filling in cereals is complex process that determines the final grain yield and quality. Abiotic stresses can have major impact on grain filling. Oats (Avena sativa L.) is sensitive to drought which adversely affect yield and productivity. In this study, we characterised the grain filling responses of two Mediterranean oat cultivars Flega and Patones under severe drought. Grains from the top (older) and bottom (younger) spikelets of primary panicle were larger in size in response to drought, particularly in Patones, suggesting accelerated grain development. The metabolomes of source (sheath, flag leaf) and sink (developing grains) tissues were profiled to describe source-sink partitioning. In Patones, the developing grains showed increased sugars and amino acids which indicate accelerated grain filling. These were associated with elevated -linolenic acid levels in source tissues but decreased in developing grains under drought. There was also a significant decrease in C18 fatty acids (FA) and jasmonates (JA) derivatives in the developing grains which suggested a role for JA signalling in Patones with drought. Flega showed a different response, with accelerated flowering and enhanced energy metabolism in both source and sink organs. The accumulation of ophthalmic acid in grains of Flega and lower levels of reduced glutathione in source tissues suggested greater oxidative stress than Patones under drought may be driving the grain filling phenotype. This study suggests that oats cultivars can use -linolenic acid-linked signalling or oxidative events influences accelerated grain filling with drought. These could be important traits in developing oat cultivars that maintain yield in drought-prone environments. HighlightThe impact on drought in one tolerant and one susceptible oat cultivar was assessed at the grain filling stage. The drought tolerant cultivar, Patones, showed accelerated grain development which could be a strategy to escape drought. Metabolite mapping of flag leaves, sheath and grains of Flega suggested that alpha linolenic acid could be regulating the altered sink-source relationships. The drought susceptible cultivar, Metabolomics shifts in Flega suggested that oxidative stress accelerated flowering.