Gibberellins and sorghum development

Abstract

Sorghum (Sorghum bicolor (L.) Moench) hybrids adapted for grain (cv. Northrup King X8102) or forage production (cv. Pride PF70) were grown in field trials at Lethbridge, Alta., Canada, and shoot cylinders containing the apical meristems were harvested at various developmental stages for analyses of endogenous gibberellin-like (GA-like) substances. Extracts were purified and chromatographed on sequential SiO2 partition columns and C18 reversed-phase high-performance liquid chromatography, and GA-like substances were detected and quantified by the cv. Tan-ginbozu dwarf rice microdroop assay. Concentrations of GA-like substances in the shoots were higher during vegetative growth than during shoot elongation or panicle elongation and the pattern of declining concentration of GA-like substances was observed for both hybrids over both field seasons. The qualitative distribution of GA-like substances was generally similar across hybrids and developmental stages, with a GA19-like substance accounting for about 60% of the total GA-like activity (GA19 is a native GA of sorghum). The exogenous application of GA3 promoted height growth and inhibited tillering, with maximal effects occurring when application was early, during rapid vegetative growth. Applications of GA3 subsequent to panicle initiation promoted panicle elongation but did not alter the time of anthesis. These results on endogenous GA concentration and response to exogenous GA3 application suggest a role for endogenous GAs in the control of shoot growth and development in sorghum.