Sodium silicate and calcium silicate differentially affect silicon and aluminium uptake, antioxidant performance and phenolics metabolism of ryegrass in an acid Andisol

Abstract

Evidence indicates that silicon (Si) alleviates diverse stresses by improving the antioxidant capacity and phenolics metabolism of plants. We assessed the effect of sodium silicate (Na2SiO3) and calcium silicate (CaSiO3) on Si and aluminium (Al) uptake, antioxidant performance and phenolics (with antioxidant or structural function) of ryegrass cultivated on an acid Andisol under greenhouse conditions. Ryegrass was treated with either sodium silicate or calcium silicate at gradually increasing doses (250, 500 and 1000 mg Si kg–1 soil). Yield and concentrations of Si and Al were measured in roots and two shoot cuts. At the first cut, phenols, antioxidant enzymes, antioxidant capacity, lipid peroxidation and lignin production and composition were also determined. Ryegrass supplied with sodium silicate exhibited the highest Si content. Root Si was closely correlated with Al or Si : Al ratio. Shoot Si uptake increased total phenols and activities of antioxidant enzymes (CAT, APX and POD), but reduced lipid peroxidation. Silicon also changed the lignin production and composition in shoots at the highest sodium silicate dose. Silicon uptake reduced the deleterious effect of soil acidity in ryegrass. Sodium silicate had the greatest influence on the antioxidant system through enhancement of phenols production and antioxidant enzyme activation. Peroxidase activity appears to be associated with increased lignin biosynthesis in plants supplied with sodium silicate.

Silicon Improves the Production of High Antioxidant or Structural Phenolic Compounds in Barley Cultivars under Aluminum Stress

“…There are evidences have shown that Si can counteract the effects of excess of certain metals (e.g., Zn, Fe, Cu, Cd, Cr, Mn, As) [10,[38][39][40][41][42] by promoting: (i) cell wall-binding [10], (ii) modification of gene expression of PAL enzyme [38], (iii) phenotypical structural alterations that increase root length [39], (iv) changes to the number of leaves per plant and leaf area [40], and (v) changes to the thickness of epidermal layers of the leaf [41]. With respect to Al toxicity in particular, some studies have proposed that Si may reduce plant stress by promoting: (i) increases in the solution pH [43], (ii) the formation of aluminosilicates in the growth media and cell wall [43,65,66], (iii) the release of phenolic compounds by the root tips [47,60], (iv) increment of carotenoids and chlorophyll in leaves [67], and (v) stimulation of antioxidant enzyme activities and antioxidant compound production [23,44]. Nevertheless, there is still a controversial debate regarding the mechanisms implicated in the Si-mediated the attenuation of Al toxicity.…”

“…Over recent years, it has been shown that Si enhances the primary metabolism by improving photosynthesis [11,16,17] and nutrient uptake [18], as well as the secondary metabolism through stimulation of the production of phenolic compounds with either antioxidant (e.g., flavonoids) or structural (e.g., lignin) functions [19][20][21]. Therefore, it has been reported that Si causes improvement in either antioxidant or structural phenols metabolism of plants under stressful environmental conditions [19,20,22,23]. This occurs via the regulation of the transcript level or activity of enzymes involved to phenylpropanoid pathway (e.g., phenylalanine ammonia lyase, peroxidase) [23][24][25], formation of lignin-carbohydrate complexes [26,27], and direct complexation of Si with polyphenolic compounds [22].…”

“…Therefore, it has been reported that Si causes improvement in either antioxidant or structural phenols metabolism of plants under stressful environmental conditions [19,20,22,23]. This occurs via the regulation of the transcript level or activity of enzymes involved to phenylpropanoid pathway (e.g., phenylalanine ammonia lyase, peroxidase) [23][24][25], formation of lignin-carbohydrate complexes [26,27], and direct complexation of Si with polyphenolic compounds [22].…”

“…Silicon is currently viewed as a sustainable alternative to provide tolerance to various metals including zinc (Zn), iron (Fe), copper (Cu), cadmium (Cd), chromium (Cr), manganese (Mn), arsenic (As), and Aluminum (Al) [10,23,[38][39][40][41][42]. Accordingly, the amelioration of Al toxicity by Si has so far been demonstrated in numerous crops, including rice, wheat, maize, sorghum, ryegrass, and soybean [12,23,[43][44][45]. In addition, some research has indicated that Si supply could stimulate plant growth processes and decrease the intensity of lipid oxidative damage [23,44,46].…”

“…Accordingly, the amelioration of Al toxicity by Si has so far been demonstrated in numerous crops, including rice, wheat, maize, sorghum, ryegrass, and soybean [12,23,[43][44][45]. In addition, some research has indicated that Si supply could stimulate plant growth processes and decrease the intensity of lipid oxidative damage [23,44,46]. However, the mechanisms induced by Si against Al stress are not yet entirely clear.…”