Induction of ApL3 expression by trehalose complements the starch-deficientArabidopsis mutant adg2-1 lacking ApL1, the large subunit of ADP-glucose pyrophosphorylase

The disaccharide trehalose has strong effects on plant metabolism and devel opment. In Arabidopsis seedlings, growth on trehalose-containing medium lea ds to an inhibition of root elongation, an accumulation of starch in the sh oots, an increased activity of ADP-Glc pyrophosphorylase (AGPase), and an i nduction of the expression of the AGPase gene, ApL3 (A. Wingler, T. Fritziu s, A. Wiemken, T. Boiler, R.A. Aeschbacher [2000] Plant Physiol 124: 105-11 4). We used Arabidopsis mutants deficient in starch synthesis to examine wh ether the primary effect of trehalose was to affect carbohydrate allocation by the induction of AGPase in the photosynthetic tissue. In a mutant lacki ng the large AGPase subunit, ApL1, (aclg2-1 mutant) growth on trehalose res tored AGPase activity and led to a strong accumulation of starch in the sho ots. In contrast, starch synthesis could not be induced in a mutant lacking the small AGPase subunit, ApS, (adg1-1 mutant) or in a mutant lacking plas tidic phosphoglucomutase (pgm1-1 mutant). These results indicate that ApL3 can substitute for ApL1 in the AGPase complex. In addition, root elongation in the mutants, especially in the adg1-1 mutant, was partially resistant t o trehalose, suggesting that the induction of ApL3 expression and the resul ting accumulation of starch in the shoots were partially responsible for th e effects of trehalose on the growth of wild-type plants.