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Poly(A) polymerase in dormant embryos of Triticum durum

Grilli, I., Pollone, E., Meletti, P.
Annals of botany 1999 v.84 no.1 pp. 71-77
Triticum turgidum subsp. durum, embryo (plant), dormancy, DNA-directed RNA polymerase, dormancy breaking, temperature, enzyme activity, seed germination, cycloheximide, messenger RNA, abscisic acid, gibberellic acid, enzyme inhibitors, chemical constituents of plants
Triticum durum 'Cappelli' has a 'relative' dormancy which can be broken by dry after-ripening at room temperature. The breakage of dormancy in the embryos of T. durum, is accompanied by a decline in content and a different degree of synthesis of poly(A)+ RNA. This work studies the activity of poly(A) polymerase (E.C., the enzyme which permits polyadenylation. An increase in the activity of this enzyme in parallel with the enhanced rate 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 cycloheximide and cordycepin shows the presence of enzymes with different origins: a stored 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 mainly active in non-dormant embryos. Since dormancy could be the result of an 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 embryos. Cycloheximide applied to excised wheat embryos represses the stimulatory and inhibitory effects of GA(3) and ABA, respectively. The hormone action on poly(A) polymerase activity is thus dependent on de novo protein synthesis. Results using cordycepin suggest the presence of a stored mRNA for poly(A) polymerase, together with hormonal regulation of enzyme activity at a translational level.