Relationship between gibberellins, height and stress tolerance in barley (Hordeum vulgare L.) seedlings
Barley cv. Perth treated with two classes of plant growth regulators, a triazole (paclobutrazol) and two acylcyclohexanediones (trinexapac-ethyl and prohexadione-Ca) that inhibit gibberellin (GA) biosynthesis at different stages were exposed to either heat or paraquat stress. They exhibited a strong quadratic regression between height and tolerance to heat stress, with paclobutrazol-treated plants being the shortest and most tolerant. This suggested that lower GA levels enhance stress tolerance, since shoot-height is closely related to GA levels. In order to determine the role of height in stress tolerance, a comparison of stress tolerance in barley GA-responsive ('dwf1' and MC96) and GA-non-responsive ('Dwf2' and MC90) mutants was conducted. Both of the GA-non-responsive mutants, 'Dwf2' and MC90, showed damage due to stress, although 'Dwf2' was significantly shorter than MC90. The 'dwf1' mutant had one-tenth the levels of total growth-active GAs compared to the two least tolerant genotypes, cv. Perth and 'Dwf2', and was the most stress tolerant. This confirmed that the endogenous GA level and its subsequent effect on height, was possibly a major factor in imparting stress tolerance in higher plants.