Exogenous short-term silicon application regulates macro-nutrients, endogenous phytohormones, and protein expression in Oryza sativa L

Abstract

Background: Silicon (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.

Results: Exogenous 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.

Conclusions: In 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.

Keywords: Gibberellins; Glucose-6-phosphate isomerase; Importin alpha 1b; Jasmonic acid; Protein expression; Radioisotope 45Ca; Silicon application.

Fig. 1

Changes in the levels of gibberellin (GA₁) and its precursors (GA₁₉ and GA₂₀) in rice plants in response to different concentrations of Si. The different letter(s) indicates significant differences at P < 0.05 according to Duncan’s multiple range test (DMRT). Each bar shows the standard error of the means of three replications

Fig. 2

Regulation of endogenous jasmonic acid (JA) levels in rice plants after the exogenous application of different concentrations of Si. The different letter(s) indicate significant differences at P < 0.05 according to Duncan’s multiple range test (DMRT). Each bar shows the standard error of the means of three replications

Fig. 3

Influence of different concentrations of Si application on endogenous salicylic acid (SA) levels in rice plants. In the figure, different letters indicated significant differences at P < 0.05 according to Duncan’s multiple range test (DMRT). Each bar shows the standard error of the means of three replications

Fig. 4

Changes in calcium uptake under Si application in rice plants. In Figure (a), the color closest to red indicates higher uptake of ⁴⁵Ca, whereas the color closest to blue indicates lower uptake of ⁴⁵Ca. Figure (b) shows quantities of ⁴⁵Ca at different leaf positions. Each bar shows the standard error of the means of three replications

Fig. 5

Effects of Si application on nitrogen uptake in rice plants. Figure (a) shows the ¹⁵N ratio in rice plants at 6 h exposure and Figure (b) indicates the ¹⁵N ratio in rice plants at 12 h exposure. Each bar shows the standard error of the means of three replications

Fig. 6

Expressions of protein levels in rice plants after exposure to short-term Si application. In the figure, red circles reveal upregulated protein spots as compared to that of the control, and blue circles indicate downregulated protein spots relative to that of the control

Fig. 7

The mRNA expression of G6P and IMP3 in rice plants after Si application. Plant samples were collected at 4 h, 12 h, 16 h and 20 h after Si treatment. In the figure, a vertical bar means standard ± standard deviation (n = 3)