Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2015
Publication Date: 2/1/2016
Citation: Suttle, J.C., Olson, L.L., Lulai, E.C. 2016. The Involvement of Gibberellins in 1,8-Cineole-Mediated Inhibition of Sprout Growth in Russet Burbank Tubers. American Journal of Potato Research. 93(1):72-79.
Interpretive Summary: For an indeterminate period of time following harvest, potatoes will not sprout and are physiologically dormant. Dormancy is gradually lost during postharvest storage and the resultant sprouting is detrimental to the nutritional and processing qualities of potatoes. Because of this, sprouting results in severe financial loss to producers. Currently sprouting is controlled through the use of synthetic sprout inhibitors. The research being conducted in this project is directed towards: 1.) identifying key physiological processes that naturally regulate tuber dormancy and, ultimately, 2.) modifying these processes genetically thereby eliminating the need for artificial sprout suppression. Previous research from this laboratory has demonstrated that dormancy exit and the onset of sprout growth is dependent on an increase in the content of growth-promoting hormones including gibberellins. In this paper, the mode of action of a novel natural-product based sprout inhibitor (cineole) was determined. The results demonstrated that, at low treatment levels, cineole did not directly inhibit either cell division or elongation but reversibly inhibited growth in a manner suggestive of hormone imbalance. Additional research showed that cineole treatment blocked the synthesis of gibberellins at a specific stage and cineole-mediated sprout growth inhibition could be completely reversed by the application of gibberellins. This is the first report demonstrating that alteration of internal hormone content is an effective method to control postharvest sprouting and suggests that other compounds known to affect hormone content may be useful sprout inhibitors in commercial storages.
Technical 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.