EFFECTS OF ABSCISIC-ACID ON RESERVE DEPOSITION IN DEVELOPING ARABIDOPSIS SEEDS

Arabidopsis thaliana mutants that were either ABA-deficient (aba1-1) o r ABA-insensitive (abi3-1) and their recombinant (aba1-1, abi3-1) were used to determine whether ABA plays a role in the regulation of depos ition of reserve material during seed development. The total net impor t of assimilates into seeds of these genotypes was unaffected compared to wild-type seeds, but the distribution of these assimilates over th e various types of storage material depended on the genotype. All muta nts were to the same extent impaired in the synthesis of long-chain fa tty acids: their seeds contained three times less eicosenoic acid (20: 1) in the triacylglycerol fraction compared to wild-type seeds. Moreov er, recombinant (aba1-1, abi3-1) seeds accumulated considerably less n eutral lipids than wild-type and single-mutant seeds, and simultaneous ly the amounts of soluble carbohydrates and starch were increased. Abs ence of and insensitivity to ABA apparently cause inhibition of acyl-c hain elongation and of lipid accumulation, and as a result a higher pr oportion of the imported assimilates is stored as carbohydrates.