The gibberellin content and early seedling growth of plants of Phaseolus vulgaris treated with the growth retardant CCC

Abstract

1. The effect of CCC applied at 10-2 M to plants of Phaseolus was followed. 2. Dry seeds did not contain extractable gibberellin. During germination of control plants gibberellin content increased markedly between days 3 and 4; but then tended to decline. For plants which emerged into light conditions, synthesis of gibberellins was noted. Treatment with CCC at planting delayed the appearance and reduced the level of extractable gibberellins, but did not prevent their appearance in appreciable quantity (up to 7.2×10-8 g plant). CCC treatment on day 7 inhibited the gibberellin production noted in light-grown plants. 3. Three zones of gibberellin activity were found on the thin layer chromatograms of plant extracts. Two of these zones corresponded with the running position of gibberellins A 8 and A 5 in our solvent system. 4. Treatment with CCC retarded the loss of fresh, dry and ethanol-insoluble weight of the cotyledons, which also showed, on a unit weight basis, a lower respiration rate. Hydrolytic activity of the cotyledons, as estimated by amylase activity, was slightly lower in treated cotyledons, which also showed a lower rate of loss of insoluble nitrogen. 5. Failure of the stems to elongate in treated plants was associated with a reduction in stem dry weight and an increase in leaf dry weight. Final dry weight of treated and control plants was similar. 6. It is suggested that CCC acts by inhibiting gibberellin synthesis. Because of this inhibition of synthesis, the onset of hydrolytic activity in the cotyledons is retarded so that liberation of preformed, bound gibberellin is delayed but not prevented. Failure of the stem to elongate is attributed to lack of gibberellin, and it is postulated that because of this, dry matter from the cotyledons is diverted to the leaves.