Changes in the endogenous concentrations of gibberellins, IAA, and ABA during the growth of different sorghum genotypes

Abstract

An early and late maturing sorghum genotype, 60M and 90M respectively, were analyzed to determine the endogenous levels of IAA, ABA, and gibberelllns. Previous experiments had Indicated that the gibberellin, GA3, hastens floral initiation in sorghum when applied under certain conditions. After a prolonged period of investigative work, the analysis of IAA and ABA was accomplished on high performance liquid chromatography (HPLC); gibberelllns were assayed with the lettuce hypocotyl elongation bloassay. The pattern of phytohormone levels was determined in 60M and 90M over a period of 35 days after planting. Plants were harvested every 5 days beginning on the 10th day after planting and continuing through day 35. The level of detectable phytohormones began to increase in both genotypes between the 10th and 15th day of growth. After 20 to 25 days of growth, the level of free IAA and ABA began to decline in both genotypes but remained significantly higher in the later maturing genotype, 90M. The high level of free IAA and ABA in 90M relative to 60M was maintained throughout the additional 15 days of the experiment. The changes in glbberellin levels did not differ between the genotypes. Therefore, delayed maturity in 90M versus 60M was attributed to the Inhibition or suppression of floral induction imposed by higher levels of free IAA and ABA.