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United States Department of Agriculture

Agricultural Research Service

Title: Postharvest Changes in Endogenous Cytokinins and Cytokinin Efficacy in Potato Tubers in Relation to Bud Endodormancy

Author
item Suttle, Jeffrey

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 20, 1998
Publication Date: N/A

Interpretive Summary: For a finite 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 lab 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. In this paper, we have shown that physiologically important changes in the internal levels of growth-promoting hormones (the cytokinins) occur well- before any changes in dormancy status can be detected. We further show that injection of these hormones into dormant tubers results in the premature termination of dormancy and enhanced sprout growth. These results suggest that modification of tuber cytokinin levels may offer a novel method to regulate tuber dormancy without resorting to the use of synthetic growth inhibitors. This possibility is currently being tested in this lab.

Technical Abstract: Using an indirect ELISA, the effects of postharvest storage duration and temperature on endogenous cytokinins in potato tuber apical bud tissues in relation to endodormancy status were determined. Following fractionation by HPLC, a total of eight cytokinins were detected and these included: zeatin riboside -5'-monophosphate (ZRMP), zeatin-O-glucoside (ZOG), zeatin (Z), zeatin riboside (ZR), isopentenyl adenosine-5'-monophosphate (IPMP), isopentenyl adenine-9-glucoside (IP-9-G), isopentenyl adenine (IP) and isopentenyl adenosine (IPA). Regardless of postharvest storage temperature or endodormancy status, IP-9-G was the most abundant cytokinin detected while ZRMP and ZOG were the least abundant cytokinins present. In tubers preincubated at a growth-permissive temperature (20C) prior to extraction, the loss of endodormancy was preceded by significant increases in the endogenous levels of Z, ZR and IPMP. When stored continuously at a growth-inhibiting temperature (3C), significant increases in ZR and IP+IPA were observed. The total content of cytokinins increased by over seven- fold during postharvest storage and this increase was a result of de-novo biosynthesis. With the exception of IP-9-G, injection of any of these cytokinins resulted in the rapid and complete termination of tuber endodormancy. Dose-response studies using IPA and ZR demonstrated a time- dependent increase in apparent cytokinin sensitivity during postharvest storage. The significance of these results with respect to endodormancy regulation and the possible mechanisms controlling cytokinin levels in potato tubers are discussed.

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