Neutral growth inhibitors in light‐grown dwarf pea shoots –separation, identification and growth regulation

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To correlate endogenous growth inhibitors of dwarf pea to its dwarfism a thorough search of growth inhibitors was made in the neutral fraction of an acetone extract from the shoots of light‐grown seedlings of Pisum sativum L. cvs Progress No 9 and Alaska. From both cultivars six inhibitors were separated and named A‐1, A‐2, A‐3, B‐1, B‐2 and B‐3 based on their order of elution from the silica gel column. Their contents as determined by cress root bioassay were: in cv. Progress 0.40, 16.5, 6.36, 1.02, 0.11 and 0.10, and in cv. Alaska 0.33, 2.35, 3.51, 0.95, 0.10 and 0.09 cress units (g fresh weight)−1. Their contributions to growth regulation of the relevant pea plants were estimated as the products of the above‐stated contents times the ratios of the specific activities of each standard sample in the cress roots and the relevant pea cultivars, and they were; in cv. Progress A‐2, 5.44 and A‐3, 2.10, and in cv. Alaska A‐2, 0.68 and A‐3, 0.88, those of A‐2 and A‐3 constituting more than 90% of the total contribution of the six inhibitors in either cultivar. The great differences in the content and contribution to growth regulation of A‐2 and A‐3 between the two cultivars suggest that the higher contents of and greater responsiveness to the two inhibitors in cv. Progress may be causes of dwarfism of this cultivar. A‐l and A‐3 were spectroscopically identified with pisatin and a mixture of cis, trans–, and trans, trans xanthoxins.