Hormonal Changes in the Stem Apex of the Cauliflower Plant in Relation to Curd Development

Abstract

SummaryThe correlation between curd development and changes in endogenous hormones in the stem apex of cauliflower plants was investigated. In particular, plants raised normally were compared with equivalent plants given a 2-week cold treatment when 6 weeks old. Hormones were extracted and assayed from the two groups of plants from the time of seedling emergence until they were 10 weeks old. Hormone activity was high in the young seedlings but gradually decreased with age. Gibberellin activity increased in the apices after 6 weeks, with a further peak after 9 weeks, at which time the morphological changes associated with curd development were detected in a small proportion of the apices sampled from untreated plants. Both gibberellin peaks were enhanced by cold treatment. An increase in auxin activity was apparent in cold-treated plants, concurrent with the first gibberellin peak, but cytokinin activity was reduced by cold treatment. The physiological implications of these results are discussed.