Cyclic Purine Mononucleotides: Induction of Gibberellin Biosynthesis in Barley Endosperm

Abstract

The de novo synthesis of α‐amylase in barley endosperm and isolated aleurone layers is induced by 3′,5′‐cyclic purine mononucleotides and gibberellic acid. The induction of α‐amylase by cyclic purine mononucleotides is prevented by 2,4‐DNP, inhibitors of RNA and protein syntheses, CCC, AMO‐1618 and phosfon. The induction of α‐amylase formation by 3′,5′‐cyclic purine mononucleotides, but not by gibberellic acid, is also blocked by inhibitors of DNA synthesis. Extracts from cyclic AMP‐treated endosperm halves exhibit a characteristic gibberellin‐like activity which is detectable within 12 hours from the addition of the cyclic AMP. On paper chromatograms this gibberellin‐like activity is located at the Rf typical for GA3. Its formation is prevented by inhibitors of DNA synthesis, CCC and AMO‐1618. Glucose inhibits the formation of α‐amylase induced by gibberellic acid. Glucose has no effect on the cAMP‐induced gibberellin biosynthesis. The evidence shows that the cyclic purine mononucleotides induce DNA synthesis, which results in gibberellin biosynthesis, which in turn activates the synthesis of α‐amylase.

Regulation of a Plant 5′(3′)-Ribonucleotide Phosphohydrolase by Cyclic Nucleotides and Pyrimidine, Purine, and Cytokinin Ribosides

“…However, other specific enzyme reactions may also be regulated by these compounds in higher plants, and it is relevant to note the diversity of responses evoked by cyclic nucleotides in higher plant systems. cGMP (Ki = 1.6 MM) applied at 1 mM has been shown to mimic GA3 in a-amylase induction and enhancement of reducing sugar production in barley aleurone (28) and to have GA-like effects in flowering induction in perennial plants (28). 8-Bromo cAMP (Ki = 26,M) and 8-bromo 5'-AMP (Ki = 9.1 ,uM) applied at 0.1 mM, both mimic the effect of kinetin (0.5 mg/liter) in promoting growth (by cell division) of excised tobacco pith parenchyma tissue (36).…”

“…cAMP (Ki = 3.4 ,uM) applied at millimolar levels to barley aleurone mimics the effect of GA3 on induction of a-amylase (18,19,28), secretion of soluble sugar (28), induction of phosphatase (20-22), and induction of protease (20). At these levels, cAMP also stimulates the effect of GA but not of kinetin on lettuce seed germination (25).…”

“…Elevation of cAMP levels in Avena coleoptiles occurs as a consequence of indole-3-acetic acid treatment (4). In phytohormone-replacement experiments, cAMP has been shown to apparently mimic responses to indole-3-acetic acid (8,(15)(16)(17) and GA (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29) in appropriate bioassays.…”