Silicon-Mediated Alleviation of Aluminum Toxicity by Modulation of Al/Si Uptake and Antioxidant Performance in Ryegrass Plants

Abstract

Silicon (Si) has been well documented to alleviate aluminum (Al) toxicity in vascular plants. However, the mechanisms underlying these responses remain poorly understood. Here, we assessed the effect of Si on the modulation of Si/Al uptake and the antioxidant performance of ryegrass plants hydroponically cultivated with Al (0 and 0.2 mM) in combination with Si (0, 0.5, and 2.0 mM). Exposure to Al significantly increased Al concentration, mainly in the roots, with a consequent reduction in root growth. However, Si applied to the culture media steadily diminished the Al concentration in ryegrass, which was accompanied by an enhancement in root dry matter production. A reduced concentration of Si in plant tissues was also observed when plants were simultaneously supplied with Al and Si. Interestingly, Si transporter genes (Lsi1 and Lsi2) were down-regulated in roots after Si or Al was applied alone; however, both Lsi1 and Lsi2 were up-regulated as a consequence of Si application to Al-treated plants, denoting that there is an increase in Si requirement in order to cope with Al stress in ryegrass. Whereas Al addition triggered lipid peroxidation, Si contributed to an attenuation of Al-induced oxidative stress by increasing phenols concentration and modulating the activities of superoxide dismutase (SOD), catalase, peroxidase, and ascorbate peroxidase antioxidant enzymes. Differential changes in gene expression of SOD isoforms (Mn-SOD, Cu/Zn-SOD, and Fe-SOD) and the profile of peroxide (H2O2) generation were also induced by Si in Al-stressed plants. This, to the best of our knowledge, is the first study to present biochemical and molecular evidence supporting the effect of Si on the alleviation of Al toxicity in ryegrass plants.

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.…”

“…In this context, some studies have found an enhancement in the antioxidant system due to the action of Si under different stresses. Consequently, the increased production of flavonoids [47], activated antioxidant enzymes [17,23,44,46], decreased lipid peroxidation of the membranes [68], regulation of gene expression, and activation of key enzymes of the phenylpropanoid pathway [16,20,44,69] have all been identified.…”

“…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.…”

Proteomic Analysis Reveals the Dynamic Role of Silicon in Alleviation of Hyperhydricity in Carnation Grown In Vitro

“…Although it is considered as a non-essential element in higher plants, this element is routinely supplied to several crops like rice and sugarcane to obtain high and sustainable crop yield [ 28 ]. In addition, it has also been observed that Si has a dynamic role in alleviating biotic and abiotic stress in plants such as pests and pathogens [ 29 , 30 ], metal toxicity [ 31 , 32 , 33 , 34 , 35 , 36 , 37 ], drought stress [ 38 , 39 ], mineral deficiency [ 40 ], salt stress [ 41 , 42 ], and UV-B stress [ 43 ]. The positive effects of Si have been largely observed in several crop plants such as wheat, barley, rice, cucumber, tomato, and soybean [ 44 , 45 , 46 , 47 ].…”