The level of jasmonic acid (JA) in medullary tissues of intact potato tubers was found to be very low [ca. 4 ng (g fr wt)−1]. When the tissues were excised and incubated on moistened filter paper, the level of JA began to increase rapidly, reached a maximum 4 h after excision and decreased thereafter. The maximum level of JA observed after 4 h was 450 ng (g fr wt)−1. The level of JA-related compounds, as estimated by a bioassay for potato tuber-inducing activity, showed similar fluctuations to those in the level of JA, and neither methyl jasmonate nor tuberonic acid could be detected in the tissues at any time. These results suggest that the increase in the level of JA is due to the synthesis of JA and the decrease is due to the degradation of JA. The accumulation of JA was found only in tissues of dormant tubers that had been stored for less than 5 months and not in those of sprouting tubers. Two inhibitors of animal phospholipase A2, namely, manoalide and quinacrine, did not inhibit the accumulation of JA, a result that suggests that activation of phospholipase A2is not involved in the synthesis of JA. Actinomycin D and chloramphenicol also had no effect on the accumulation of JA but cycloheximide had a considerable inhibitory effect. The results suggest that a newly synthesized protein(s) is the ratelimiting factor in the biosynthesis of
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