ABSTRACT
Analysis of endogenous growth regulators requires extraction procedures that destroy the in vivo compartmentation of the compounds which may grossly affect our estimates of a biologically active fraction. Extractions also provide a static picture of substances which are in a dynamic state; at any time their concentration is the outcome of their biosynthesis, accumulation, and metabolism. Sex expression in cucumber is correlated with endogenous ethylene production. Exogenous applications of ethylene cause flower abortion in different species suggesting that this substance participates in the endogenous control of flower development. The data are clearly consistent with the idea that Gibberellins is the stimulus for dormancy release in coffee flower buds. Cytokinins have been identified in flowers and inflorescences of some species; however, changes in their endogenous level during reproductive development do not permit simple interpretation. Abscisic acid levels fluctuate in dormant buds, being relatively high near the end of the rest period, and then decreasing with sufficient chilling to break dormancy.
