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United States Department of Agriculture

Agricultural Research Service

Title: Changes in Cis-Zeatin and Cis-Zeatin Riboside Levels and Biological Activity During Potato Tuber Dormancy.

Authors
item SUTTLE, JEFFREY
item Banowetz, Gary

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 28, 1999
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. Much of our current research concerns the roles of plant hormones in the regulation of tuber dormancy. In this paper, we report on changes in the internal levels of an unusual class of plant hormones (cis-zeatins). In addition, we describe the ability of these hormones to artificially terminate tuber dormancy. This is the first published report that describes the relationship between this class of hormones and any form of plant dormancy. The results presented are consistent with a role for these hormones in tuber dormancy regulation and suggest that these compounds may be of use in prematurely terminating dormancy. The results further suggest that tuber dormancy may be extended by blocking the synthesis or action of these cytokinins.

Technical Abstract: The effects of postharvest storage duration and temperature on endogenous cis-zeatin and cis-zeatin riboside levels in potato (Solanum tubersum L.)tubers were determined in relation to tuber bud dormancy. The tubers used in these studies were completely dormant for at least 81 days of storage. Thereafter tuber bud dormancy diminished gradually and after 165 days of postharvest storage, the tubers were completely non- dormant. Immediately after harvest, endogenous levels of cis-zeatin and cis-zeatin riboside were approximately 25 pmol g-1 fresh weight (FW) and 8 pmol g-1 FW, respectively. In tubers stored at a growth-inhibiting temperature (3C), endogenous levels of cis-zeatin rose over 3-fold after twenty five days of storage and remained elevated for the duration of the study. Levels of cis-zeatin riboside remained essentially constant during this same period. In tubers transferred to a growth permissive temperature (20C) prior to use, the rise in endogenous cis-zeatin was less dramatic and more protracted; increasing two-fold after 53 days of storage. No change in cis-zeatin riboside content was observed in these tubers during this period. Dose-response studies using either cis- zeatin or trans-zeatin demonstrated a time-dependent increase in cytokinin sensitivity during postharvest storage. Immediately after harvest, dormant tubers were insensitive to both zeatin isomers. Thereafter tubers exhibited a dose-dependent increase in premature sprouting following injection with either cytokinin isomer. After injection into dormant tubers, cis[8-14C]-zeatin was metabolized primarily to adenine/adenosine and cis-zeatin riboside. Seven days after injection, less than ten percent of the recovered radioactivity

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