Abstract

The involvement of gibberellins in 1,8-cineole-mediated inhibition of tuber sprout growth was investigated in non-dormant field- and greenhouse-grown tubers of Russet Burbank. Continuous exposure of tubers to cineole in the vapor-phase resulted in a dose-dependent inhibition of sprout growth. Comparative studies using plant bioassay systems whose growth was differentially dependent on cell division, cell elongation, or both demonstrated that cineole had no direct effect on either process. Of the assays used, only cineole-mediated inhibition of etiolated hypocotyl growth mirrored the inhibition of tuber sprout growth which suggested an effect on gibberellin synthesis or action. Both GA19 and GA20 were detected in extracts prepared from control sprouts but only GA19 was found in extracts prepared from cineole treated sprouts. Exogenous GA3, GA20, and GA1 (but not GA19) reversed cineole-mediated sprout growth inhibition. Expression of genes encoding key GA metabolic enzymes was altered by cineole treatment in a manner consistent with diminished endogenous GA content. Collectively, these results suggest that the inhibition of sprout growth by low vapor-phase concentrations of cineole is in part a result of impaired GA biosynthesis resulting in a reduction in bioactive GA content.

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