Abstract Background Exogenous hormone applications modify the plant growth and development by inducing changes in their endogenous contents. However, it is not clear whether the effects of exogenous hormones on growth are direct or related with changes induced in endogenous hormones. Laboratory and greenhouse experiments were conducted to study the effect of exogenous salicylic acid (SA) or indole acetic acid (IAA) on endogenous levels in soaked seeds, 5-day-old seedlings, and in vegetative growth of foliar-sprayed plants. The effects of different concentrations of two hormones on germination and growth of maize were also studied.Results The effect of presoaking maize seeds in solutions of SA or IAA (0, 0.25, 0.5, 1, and 2 mM) on their endogenous contents in soaked seeds or in 5-day-old seedlings. Soaked seeds absorbed more SA than IAA. In young seedlings, the majority of two hormones which absorbed during seed soaking remained in the residual seeds. Presoaking seeds in SA or IAA solutions suppressed the growth of 5-day-old seedlings. In the greenhouse experiment, endogenous SA and IAA increased after spraying two compounds at 0.25–2 mM, peaking 2 days after treatment then decreased on. However, plants treated with SA at 1 mM or 2 mM continued to pose higher levels of endogenous SA, 8 days later. At 20 days after treatments, all tested concentrations of two hormones significantly increased the fresh and dry weights of the whole plant. These inducing effects disappeared 40 days after spraying.Conclusion The obtained results demonstrated the changes in endogenous SA and IAA in soaked seeds, seedling, and foliar-sprayed plants due to their exogenous application. However, concentrations of two hormones did not produce any permanent enhancement effects on germination and plant growth.
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