Figure 1.

GA Structure and Response Mutant Categories.

(A) The structure of a bioactive GA (GA₄), showing carboxylic (C6) and hydroxyl (C3) groups that are essential for biological activity, and the C2 site, hydroxylation of which abolishes biological activity.

(B) Schematic representation of plants in GA-related mutant categories. Normal (wild type) plants respond to exogenous GA (+GA) by increased growth. GA-sensitive dwarf mutants are GA-deficient (–GA) and grow in response to exogenous GA. GA-insensitive dwarf mutants do not grow in response to exogenous GA. Finally, slender mutant growth mimics that of GA-treated normal plants, even when additional mutations or chemical growth retardants cause GA deficiency.