Involvement of Cytokinins, 3-Indoleacetic Acid, and Gibberellins in Early Fruit Growth in Pepper (Capsicum annuum L.)

Abstract

The roles of plant hormones in the early growth of pepper fruit (Capsicum annuum L.) were investigated. An exogenous hormone treatment study indicated that cytokinin (CK) was more effective at stimulating early fruit growth in two lines than auxin or gibberellin (GA). Endogenous levels of CKs, 3-indole-acetic acid (IAA), and GAs in young pollinated and unpollinated fruit of four lines (two with medium-sized and two with small fruit) were also investigated. In pollinated fruit, the level of trans-zeatin riboside (tZR) increased with fruit size. In unpollinated fruit, tZR did not increase in any lines. IAA levels decreased gradually after flowering and did not differ between pollinated and unpollinated fruit in any lines. Levels of GA₁ in unpollinated fruit of the lines in which unpollinated fruit were relatively well enlarged were slightly higher. In the line in which unpollinated fruit could not enlarge, GA₁ levels of all samples were lower than the others. These results indicate that tZR is important in the early enlargement of pollinated pepper fruit, and that GA₁ is involved in early fruit enlargement, especially in unpollinated pepper.