Poly(A) polymerase in dormant embryos of Triticum durum

Triticum durum 'Cappelli' has a 'relative' dormancy which can be broken by dry after-ripening at room temperature. The breakage of dormancy in the emb ryos of T. durum, is accompanied by a decline in content and a different de gree of synthesis of poly(A)(+) RNA. This work studies the activity of poly (A) polymerase (E.C. 2.7.7.19), the enzyme which permits polyadenylation. A n increase in the activity of this enzyme in parallel with the enhanced rat e of germination is revealed. Since poly(A) polymerase activity is the same in dormant and non-dormant dry embryos, it seems that the activity of the enzyme is not involved in the breakage of dormancy. The use of cycloheximid e and cordycepin shows the presence of enzymes with different origins: a st ored enzyme and one bound to a long lived mRNA, present in dormant and non- dormant embryos, plus an enzyme bound to newly synthesized mRNA which is ma inly active in non-dormant embryos. Since dormancy could be the result of a n interaction between hormones, this work analyses the effects of GA(3) and ABA on poly(A) polymerase. GA(3) enhanced poly(A) polymerase activity only in dormant embryos while ABA inhibited this activity only in non-dormant e mbryos. Cycloheximide applied to excised wheat embryos represses the stimul atory and inhibitory effects of GA(3) and ABA, respectively. The hormone ac tion on poly(A) polymerase activity is thus dependent on ne novo protein sy nthesis. Results using cordycepin suggest the presence of a stored mRNA for poly(A) polymerase, together with hormonal regulation of enzyme activity a t a translational level. (C) 1999 Annals of Botany Company.