Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2011
Publication Date: 4/13/2011
Citation: Suttle, J.C., Huckle, L.L., Lulai, E.C. 2011. The effects of dormancy status on the endogenous contents and biological activities of jasmonic acid, n-(jasmonoyl)-isoleucine, and tuberonic acid in potato tubers. American Journal of Potato Research. 88:283-293.
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. The plant hormone jasmonic acid (JA) has been reported to inhibit sprout growth and a patent describing its use in a commercial setting has been granted. However, the role of endogenous JA and its metabolites in the natural control of tuber dormancy has not been determined. In this paper, the contents of JA and two principal metabolites in specific tuber tissues undergoing natural and chemically forced dormancy progression were measured and the effects of applied JA and the naturally occurring isoleucine conjugate on dormancy duration and sprout growth were determined. In studies conducted over a three-year period it was demonstrated that changes in the internal contents of JA and its metabolites were not consistent with those expected of a dormancy-regulating hormone. In addition, neither JA nor its isoleucine conjugate had any effects on the length of tuber dormancy and only transiently inhibited sprout growth in non-dormant tubers. These results do not support a role for JA or its metabolites in potato tuber dormancy control.
Technical Abstract: The effects of storage and dormancy progression on the endogenous contents and the growth-regulating activities of jasmonic acid (JA), jasmonoyl-isoleucine (JA-Ile), and tuberonic acid (TA) were determined in potato (Solanum tuberosum L. cv. Russet Burbank) minitubers and seed tubers over several harvest/storage seasons. In apical discs (consisting of both periderm and buds) isolated from minitubers undergoing natural dormancy progression, JA content was low immediately after harvest, remained essentially constant as dormancy weakened, rose >4-fold as sprouting commenced and declined by > 50% as sprouting became more vigorous. JA-Ile content was more variable; remaining constant over 7 months of storage in one year and increasing ca. 5-fold over the same period during a second year. The TA content of minituber apical discs exceeded that of JA or JA-Ile by >20-fold and declined steadily to ca. 50% of initial levels during storage and dormancy progression. A similar but more temporally compressed pattern was found in chemically forced minituber apical discs following a 24 hour treatment with the synthetic dormancy terminating agent bromoethane. A different pattern was observed in meristems isolated from seed tubers at three stages of dormancy progression. JA content was low in dormant meristems and remained constant in meristems isolated at late dormancy and following dormancy exit. The content of JA-Ile rose gradually as meristems progressed from deep dormancy to active sprouting. The TA content of isolated meristems was > 20-fold higher than either JA or JA-Ile and rose slightly during dormancy progression. Exogenous JA (0.001-1 mM) had no effect on sprout growth when applied to intact non-dormant minitubers but treatment with 1 mM JA-Ile inhibited sprout growth by 35%. In contrast, direct application of 10µg JA to single-eye tissue cylinders resulted in a 29% inhibition of sprout growth after two weeks while JA-Ile had no effect. Treatment of dormant minitubers with either JA or JA-Ile (0.01-1 mM) had no effects on dormancy duration or subsequent sprout growth. Collectively, these data do not support a major role for JA or its metabolites JA-Ile and TA in potato tuber dormancy control but they do not exclude other roles for these hormones in tuber physiology and early sprout growth.