The alleviation of zinc toxicity by silicon is related to zinc transport and antioxidative reactions in rice

Abstract

The objective of this study is to elucidate the roles of silicon (Si) in enhancing tolerance to excess zinc (Zn) in two contrasting rice (Oryza sativa L.) cultivars: i.e. cv. TY-167 (Zn-resistant) and cv. FYY-326 (Zn-sensitive). Root morphology, antioxidant defense reactions and lipid peroxidation, and histochemical staining were examined in rice plants grown in the nutrient solutions with normal (0.15 μM) and high (2 mM) Zn supply, without or with 1.5 mM Si. Significant inhibitory effects of high Zn treatment on plant growth were observed. Total root length (TRL), total root surface area (TRSA) and total root tip amount (TRTA) of both cultivars were decreased significantly in plants treated with high Zn, whereas these root parameters were significantly increased when Zn-stressed plants were supplied with 1.5 mM Si. Supply of Si also significantly decreased Zn concentration in shoots of both cultivars, indicating lower root-toshoot translocation of Zn. Moreover, superoxide dismutase (SOD), catalase (CAT), and asorbate peroxidase (APX) activities were increased, whereas malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ) concentrations were decreased in Sisupplied plants of both Zn-sensitive and Znresistant rice cultivars exposed to Zn stress. These alleviative effects of Si, further confirmed by the histochemical staining methods, were more prominent in the Zn-resistant cultivar than in the Znsensitive one. Taken together, all these results suggest that Si-mediated alleviation of Zn toxicity is mainly attributed to Si-mediated antioxidant defense capacity and membrane integrity. The possible role of Si in reduction of root-to-shoot translocation of Zn can also be considered.

Effect of silicon application on Sorghum bicolor exposed to toxic concentration of zinc

“…This positive influence also has been recorded in the case of other metals and plant species, e.g. silicon ameliorates inhibitory effect of aluminium on root growth of sorghum (Hodson & Sangster 1993) and toxicity of zinc in rice (Song et al 2011). Silicon application may be useful to improve the drought tolerance of sorghum via enhancement of water uptake ability (Hattori et al 2005;Ahmed et al 2011;Sonobe et al 2011).…”

“…Their study also revealed high reduction of root biomass after Cr application and on the other hand, the presence of Ni (70 mg L −1 ) stimulated the growth of root. Significant inhibitory effects of high Zn treatment on plant growth were also observed in Zn-sensitive and Zn-resistant cultivars of rice (Song et al 2011). Total root length, total root surface area, shoot and root dry weight and total root tip number of both rice cultivars were decreased significantly in plants treated with 2 mM Zn, whereas root parameters were significantly increased when Zn-stressed plants were supplied with Si (Song et al 2011).…”

“…Significant inhibitory effects of high Zn treatment on plant growth were also observed in Zn-sensitive and Zn-resistant cultivars of rice (Song et al 2011). Total root length, total root surface area, shoot and root dry weight and total root tip number of both rice cultivars were decreased significantly in plants treated with 2 mM Zn, whereas root parameters were significantly increased when Zn-stressed plants were supplied with Si (Song et al 2011). Mitigation effect of Si was determined in maize plants grown at 0.2 mM Zn concentration in nutrient solution (Kaya et al 2009).…”

“…However, Zn toxicity occurs in soils contaminated by mining and smelting activities, in agricultural soils treated with sewage sludge, and in urban and peri-urban soils enriched by anthropogenic inputs of Zn, especially in low-pH soils (Chaney 1993). Silicon was recorded as an effective element for alleviation of Zn toxicity in some plant species (Cunha & Nascimento 2009;Kaya et al 2009;Song et al 2011).…”

Can silicon partially alleviate micronutrient deficiency in plants? a review

“…in solution calculated by the Visual MINTEQ program to be the same for all the Si treatments. In such conditions, a different Zn distribution pattern was observed in Si-treated plants with a higher metal concentration in roots either in hydroponic or in soil experiments (Gu et al 2011(Gu et al , 2012Song et al 2011). Several explanations were given: (a) Si addition contributes to the root cell wall strengthen delaying the Zn 2?…”