Effect of Si on the distribution of Cd in rice seedlings

Abstract

Growth chamber studies were conducted to investigate the effects of silicon (Si) on the distribution of Cd in rice seedlings (Oryza sativa L., cv. Qiu Guang) grown hydroponically under toxic level of cadmium (Cd). Si added significantly alleviated the toxicity of Cd in aerobic rice seedlings. Si partly overcame the reduction in growth due to Cd. This amelioration was correlated with a reduction in Cd uptake. Si increased Cd accumulation in the roots and restricted the transport of Cd from roots to shoots, where the distribution of Cd in the shoots decreased by 33%. Si reduced the transport of Cd and the apoplastic fluorescence tracer PTS (tri-sodium-8-hydroxy-1, 3, 6-pyrenesulphonate) from roots to shoots by 23 and 36%, respectively. Energy-dispersive X-ray analysis (EDX) showed Cd was mainly deposited in the vicinity of the endodermis and epidermis, Si deposition was heavier in the vicinity of the endodermis than in the epidermis. Although the tracing result of fluorescein isothiocyanate-dextrans showed Si did not change epidermal wall porosity, the significant reduction of apoplastic PTS transport in +Si plants suggested that the heavy deposition of silica in the vicinity of endodermis might offer possible mechanisms by which silicon did at least partially physically block the apoplast bypass flow across the roots, and restrained the apoplastic transport of Cd. In addition, the effect of Si on the subcellular distribution and chemical form of Cd was investigated by fractionation. Si decreased the concentrations of Cd in shoots and roots, but did not remarkably change the distribution ratio of Cd in symplasm and apoplast. Mechanisms by which Si alleviates the toxicity of Cd in rice seedlings are discussed.

Mechanisms of silicon-mediated alleviation of abiotic stresses in higher plants: A review

“…In a solution culture experiment with maize, Liang et al found that more Cd was bound to the root cell walls but less to cytosols or symplast in þSi plants than in ÀSi plants under Cd stress (unpublished data), suggesting a root apoplastic role of Si in detoxification of excess Cd, a mechanism similar to that responsible for the Si-mediated Mn tolerance in plants (Iwasaki et al, 2002a,b;Rogalla and Römheld, 2002). However, contrasting results have recently been reported by Shi et al (2005a), who have shown that most of the total root Cd (87%) was localized in the symplasm, whereas the apoplast Cd accounted for only 13% of the total in both ÀSi and þSi treatments. Furthermore, X-ray microanalysis (EDX) showed that Cd was deposited mainly in the vicinity of the endodermis and epidermis, and Si deposition was heavier in the vicinity of the endodermis than of the epidermis (Shi et al, 2005a).…”

“…The role of Si in minimizing uptake and root-to-shoot transport of metal ions has recently been confirmed in seedlings of rice grown with toxic Cd (Shi et al, 2005a) and with arsenate (Guo et al, 2005). Si also significantly reduced the transport of the apoplastic fluorescence tracer PTS (trisodium-8-hydroxy-1,3,6-pyrenesulphonate) from roots to shoots (Shi et al, 2005a), suggested that the heavy deposition of silica in the vicinity of the endodermis might offer a possible mechanism by which silicon did at least partially physically block the apoplast bypass flow across the roots, and restrained the apoplastic transport of Cd.…”

Effects of Silicon on Alleviating Arsenic Toxicity in Maize Plants

“…Silicon has been recognized as a toxicity alleviating agent in plants through retaining heavy metals in roots, inhibiting their translocation to the shoots (Shi et al, 2005a), depositing SiO 2 in the apoplast of the roots and on the leaf surface, forming a barrier to the apoplastic flow of metallic ions and to transpiration flux (Lux et al, 2002;Shi et al, 2005a). It also contributes to the co-precipitation of Si-metal complexes in the cell wall, compartmentalization of metals bound to organic acids in the vacuole (Neumann and Nieden, 2001), more homogeneous distribution of metals, formation of Si-polyphenol complexes in tissues (Maksimovic et al, 2007), and reduced lipid peroxidation in the membrane, via stimulation of enzymatic and non-enzymatic antioxidants (Shi et al, 2005b).…”

Mitigation of cadmium and arsenic in rice grain by applying different silicon fertilizers in contaminated fields

“…Evidence has suggested that silicon (Si) fertilizers are effective in reducing the concentration of Cd (Shi et al 2005;Kim et al 2014) or As in rice grain (Guo et al 2007;Seyfferth and Fendorf 2012). Various Si compounds, such as K 2 SiO 3 and silica gel, were chosen as Si fertilizers for hydroponic culture or pot experiments to mitigate Cd or As individually in rice shoots (Zhang et al 2008;Putwattana et al 2010;Marmiroli et al 2014).…”

“…The co-precipitation of Cd and Si in cell walls via Si-wallCd complexation may be one of the key target mechanisms for the reduction of Cd transportation from roots to shoots and thus the mitigation of Cd accumulation in rice grain. Furthermore, Si deposition in the vicinity of the endodermis can partially block the apoplast bypassflow across the roots and inactivate Cd apoplastic transport from roots to shoots (Shi et al 2005).…”