Involvement of josmonic acid and related compouds in morpho genesis of crop plants.

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1. Using a bioassay for tuber-inducing activity, which was carried out with cultures of single-node segments of potato stems in vitro, jasmonic acid (JA) was isolated from the leaves of Jerusalem artichoke (Helianthus tuberosus L.), and identified by both HOLC and mass spectrometry. The Level of endogenous JA in the leaves of young plants was very high (2.6x10^<-6> mol・kg^<-i>) but decreases sharply with the growth of the plants. By contrast, the level of water-soluble derivatives of JA increased with the growth of plants and reached a maximim near the tine at which tuberization was initiated. The effect of exogenous JA on the tuberization of Jerusalem artichoke plants was examined in vityo, and JA was found to have strong tuber-inducing activity. These results suggest that tuberization of Jerusalem artichoke plants is controlled by JA and related compounds.When disks cut from potato tubers were cultured on medium that contained jasmonic acid (JA), the disks began to swell markedly after one day in culture. Within five days in culture, the fresh weight of the disks doubled in the presence of JA at 3 x 10^<-5> M.Light microscopy revealed that the swelling was due to the expansion and not the division of cells. JA exhibited this expansion-inducing activity at concentrations above 10^<-5> M.Sucrose in the culture medium was not necessary for the expansion of cells. The expansion-inducing activity appeared to be specific to JA and related compounds, since various plant hormones and a precursor to ethylene had no appreciable effects on the size of cells. The expansion- inducing activities of JA and JA-Me seem to be associated with their tuber-inducing activities.