Effects of abscisic acid on reserve deposition in developing Arabidopsis seeds

Arabidopsis thaliana mutants that were either ABA-deficient (aba1-1) or ABA-insensitive (abi3-1) and their recombinant (aba1-1, abi3-1) were used to determine whether ABA plays a role in the regulation of deposition of reserve material during seed development. The total net import of assimilates into seeds of these genotypes was unaffected compared to wild-type seeds, but the distribution of these assimilates over the various types of storage material depended on the genotype. All mutants were to the same extent impaired in the synthesis of long-chain fatty acids: their seeds contained three times less eicosenoic acid (20:1) in the triacylglycerol fraction compared to wild-type seeds. Moreover, recombinant (aba1-1, abi3-1) seeds accumulated considerably less neutral lipids than wild-type and single-mutant seeds, and simultaneously the amounts of soluble carbohydrates and starch were increased. Absence of and insensitivity to ABA apparently cause inhibition of acyl-chain elongation and of lipid accumulation, and as a result a higher proportion of the imported assimilates is stored as carbohydrates.