Abscisic Acid Induces Triacylglycerol Accumulation and Lipid Remodelling in Chloroplast-Containing Green Tissues of Lemna minor

Lipid remodelling is a fundamental component of plant responses to environmental stress and development, yet its regulation in fast-growing aquatic plants remains poorly understood. Here, we investigated how abscisic acid (ABA) regulates triacylglycerol (TAG) accumulation and fatty acid (FA) composition in the duckweed Lemna minor. A 3-day treatment with 1 µM ABA induced a 2.9-fold increase in TAG content, accompanied by extensive remodelling of plastidial and extraplastidial membrane lipids. Reduced monogalactosyldiacylglycerol (MGDG) likely served as a FA source for TAG synthesis. Transcript analyses revealed strong induction of diacylglycerol acyltransferase (DGAT) genes, catalysing the final step of TAG formation, and repression of fatty acid desaturase (FAD) genes, resulting in a marked reduction in polyunsaturated FA levels. Confocal imaging confirmed substantial lipid droplet accumulation in both fronds and chloroplast-containing roots. Notably, this sustained ABA-induced TAG accumulation was unique to L. minor, with no comparable response observed in other duckweed species or in Arabidopsis under identical treatment. These findings reveal a species-specific ABA-driven lipid remodelling pathway in duckweed, linking phytohormone signalling to carbon storage in aquatic plants.