The Effects of Dormancy Status on the Endogenous Contents and Biological Activities of Jasmonic Acid, N-(jasmonoyl)-Isoleucine, and Tuberonic Acid in Potato Tubers

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 1 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 h 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 to 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 10 μg JA to single-eye tissue cylinders resulted in a 29% inhibition of sprout growth after 2 weeks while JA-Ile had no effect. Treatment of dormant minitubers with either JA or JA-Ile (0.01to1 mM) had no effect 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.