Abstract
BackgroundExogenous 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.ResultsThe 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.ConclusionThe 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.
Highlights
Exogenous hormone applications modify the plant growth and development by inducing changes in their endogenous contents
We investigated the effect of presoaking maize seeds in salicylic acid (SA) or indole acetic acid (IAA) on germination, uptake, and distribution of endogenous hormones in young seedlings
The results indicated that application SA at 0.25 Mille molar (mM) did not produce any remarkable effect on endogenous SA when compared with control, whereas spraying SA at 0.5–2 mM caused a concentration-dependent increase in SA
Summary
Exogenous hormone applications modify the plant growth and development by inducing changes in their endogenous contents. Endogenous hormones are tightly controlled through various mechanisms, such as biosynthesis, degradation, transportation, and conjugate formation (Korasick et al 2013) It is not clear whether the effects of exogenous hormones on plant growth are direct or whether they are connected with their effects on endogenous hormones (Szalai et al 2011). Moravcová et al (2018) studied the effect of pre-treatment of maize seeds with SA in different concentrations on the level of endogenous SA They found that soaking seeds in SA at 50 μM resulted in a significant increase in endogenous SA, but application 500 μM produced a significant decrease in the level of endogenous SA in the newly formed roots, whereas soaking pea seeds in SA caused increases in both free and pound SA contents in the seeds (Szalai et al 2011). Higher levels of endogenous IAA might cause an inhibitory effect, so the optimum endogenous level must be controlled. Cai et al (2018) found that at 3 days after exogenous application of SA, the endogenous SA reached the maximum and subsequently decreased until it reached the level of control plants at 7 days later
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