Abstract
BackgroundSilicon (Si) has been known to regulate plant growth; however, the underlying mechanisms of short-term exogenous Si application on the regulation of calcium (Ca) and nitrogen (N), endogenous phytohormones, and expression of essential proteins have been little understood.ResultsExogenous Si application significantly increased Si content as compared to the control. Among Si treatments, 1.0 mM Si application showed increased phosphorus content as compared to other Si treatments (0.5, 2.0, and 4.0 mM). However, Ca accumulation was significantly reduced (1.8- to 2.0-fold) at the third-leaf stage in the control, whereas all Si treatments exhibited a dose-dependent increase in Ca as determined by radioisotope 45Ca analysis. Similarly, the radioisotope 15N for nitrogen localization and uptake showed a varying but reduced response (ranging from 1.03–10.8%) to different Si concentrations as compared to 15N application alone. Physiologically active endogenous gibberellin (GA1) was also significantly higher with exogenous Si (1.0 mM) as compared to GA20 and the control plants. A similar response was noted for endogenous jasmonic and salicylic acid synthesis in rice plants with Si application. Proteomic analysis revealed the activation of several essential proteins, such as Fe-S precursor protein, putative thioredoxin, Ser/Thr phosphatase, glucose-6-phosphate isomerase (G6P), and importin alpha-1b (Imp3), with Si application. Among the most-expressed proteins, confirmatory gene expression analysis for G6P and Imp3 showed a similar response to those of the Si treatments.ConclusionsIn conclusion, the current results suggest that short-term exogenous Si can significantly regulate rice plant physiology by influencing Ca, N, endogenous phytohormones, and proteins, and that 1.0 mM Si application is more beneficial to plants than higher concentrations.
Highlights
Silicon (Si) has been known to regulate plant growth; the underlying mechanisms of shortterm exogenous Si application on the regulation of calcium (Ca) and nitrogen (N), endogenous phytohormones, and expression of essential proteins have been little understood
The magnesium (Mg) ratio was significantly increased in the 1.0, 2.0, and 4.0 mM Si treatments in comparison to the control, but no difference was observed in the 0.5 mM Si treatment as compared to the control (Table 1)
Ca uptake was significantly inhibited in relatively young leaves in comparison to older leaves and this phenomenon was confirmed by uptake of radioisotope 45Ca
Summary
Silicon (Si) has been known to regulate plant growth; the underlying mechanisms of shortterm exogenous Si application on the regulation of calcium (Ca) and nitrogen (N), endogenous phytohormones, and expression of essential proteins have been little understood. Higher plants usually take up aqueous silicic acid from the rhizosphere through their roots [12]. Ma et al [7] reported that two specific genes (OsLsi and OsLsi2) were involved in Si transfer between the rhizosphere and xylem. During transport of Si, transport-related genes are activated and calcium (in Ca2+ form) is actively taken up through the solute gradient in either an apoplastic or a
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