Hypoxia increases triacylglycerol levels and unsaturation in tomato roots

Background: Plants are designed to endure stress, but increasingly extreme weather events are testing the limits. Events like flooding result in submergence of plant organs, triggering an energy crisis due to hypoxia and threaten plant growth and productivity. Lipids are relevant as building blocks and energy vault and are substantially intertwined with primary metabolism, making them an ideal readout for plant stress.

Results: By high resolution mass spectrometry, a distinct, hypoxia-related lipid composition of Solanum lycopersicum root tissue was observed. Out of 491 lipid species, 11 were exclusively detected in this condition. Among the lipid classes observed, glycerolipids and glycerophospholipids dominated by far (78%). Differences between the lipidomic profiles of both analyzed conditions were significantly driven by changes in the abundance of triacylglycerols (TGs) whereas sitosterol esters, digalactosyldiacylglycerols, and phosphatidylcholine play a significantly negligible role in separation. Alongside, an increased level of polyunsaturation was observed in the fatty acid chains, with 18:2 and 18:3 residues showing a significant increase. Of note, hexadecatetraenoic acid (16:4) was identified in hypoxia condition samples. Changes in gene expression of enzymes related to lipid metabolism corroborate the above findings.

Conclusion: To our knowledge, this is the first report on a hypoxia-induced increase in TG content in tomato root tissue, closing a knowledge gap in TG abiotic stress response. The results suggest that the increase in TGs and TG polyunsaturation degree are common features of hypoxic response in plant roots.