Submitted to: Journal of Plant Growth Regulation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 16, 2001
Publication Date: N/A
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 lab is directed towards 1.) identifying key physiological processes that naturally regulate tuber dormancy and, ultimately 2.) modifying these processes genetically or chemically with naturally occurring sprout inhibitors thereby eliminating the need for artificial sprout suppression. Much of our current research concerns the roles of plant hormones in tuber dormancy regulation. In this paper, the role of hormone metabolism (inactivation) in controlling hormone action in potatoes during dormancy is examined. Injection of dormant tubers with the plant hormone cytokinin rapidly terminates dormancy only if the tubers have been stored for an extended period of time; freshly harvested tubers do not respond to hormone treatment. The metabolism of these hormones in freshly harvested and stored tubers was determined and it was found that neither the rate of metabolism nor the type of metabolites formed changed during storage. These results indicate that other aspects of hormone biology regulate biological activity during tuber dormancy and that these processes are critical to tuber dormancy control. The nature of these other processes is currently under study. Once identified, these "master" processes are candidates for genetic or chemical manipulation of tuber dormancy.
Technical Abstract: The metabolism of [3H]-zeatin (Z) and [3H]-isopentenyl-adenosine (IPA) in potato tubers was examined in relation to changes in cytokinin efficacy and dormancy status during postharvest storage. Immediately after harvest and during the initial period of storage, tubers were dormant and exogenous Z or IPA were completely ineffective in breaking tuber dormancy. Thereafter, dormant tubers exhibited a gradual increase in sensitivity to both cytokinins. Cytokinin sensitivity continued to increase as postharvest storage was extended and dormancy weakened. Exogenous radiolabeled cytokinins were rapidly metabolized by dormant and nondormant tubers. Following injection, [3H]-Z was metabolized to zeatin riboside, adenine derivatives and zeatin riboside-5'- monophosphate. Four hours after injection, less than 60% of the recovered radioactivity was associated with unmetabolized [3H]-Z. [3H]- IPA was also rapidly metabolized to several metabolites including: IPA- 5'-monophosphate, adenine derivatives and zeatin riboside. Four hours after injection, less than 50% of the recovered radioactivity was associated with [3H]-IPA. Dormancy status had no apparent effects on the metabolism of either cytokinin. Neither the rate of metabolism or the nature of metabolites detected was affected by the length of postharvest storage. These results suggest that changes in cytokinin efficacy in dormant potato tubers during postharvest storage are not the result of differential catabolism but rather are due to other cellular processes such as hormone perception and/or signal transduction.