Effect of Heat Stress on Indole-3-acetic Acid and Abscisic Acid Contents in Soybean of VariousDevelopmental Stages

Indole-3-acetic acid (IAA) and abscisic acid (ABA) were quantifiedin the third unfolded leaves of soybean (Glycine max L.) subjected to heat stress.Six cultivars of the ecophenotypes of North China were used in this experiment.They were Prematurity No.17 (PM17), Mutagenic Treatment No.4 (MT4),Mutagenesis No.31 (MU31), Dark-resistant Black Soybean (DBS), ScientificBumper Harvest No.6 (SBH6) alld No.34 (SBH34). When blooming began, IAAand ABA levels in the third unfolded leaves of heat stressed plants weresignificantly higher than those in non-stressed plants (30～33℃) after the first dayof treatment (43～45℃,4 h). However, after the second day of treatment (43～45℃,4 h/d), most of the endogenous IAA and ABA levels decreased sharply. Whenplants were in full bloom, they were stressed by heat (43～45℃, 4 h/d) for twoconsecutive days, and the IAA levels in most of them and the ABA levels in onehalf of them were lower than those in their non-stressed plants (30～33℃). At thestage of pod formation, plants that were heat-stressed (45℃, 4 h/d) for twoconsecutive days contained notably higher levels of IAA and ABA in the thirdunfolded leaves than those in the non-stressed plants (30～33℃). These resultssuggest that endogenous IAA and ABA regulated adversity-resistance of soybeanIn common.