Abstract
Silicon (Si) plays important roles in alleviating heavy metal stress in rice plants. Here we investigated the physiological response of rice at different growth stages under the silicon-induced mitigation of cadmium (Cd) and zinc (Zn) toxicity. Si treatment increased the dry weight of shoots and roots and reduced the Cd and Zn concentrations in roots, stems, leaves and grains. Under the stress of exposure to Cd and Zn, photosynthetic parameters including the chlorophyll content and chlorophyll fluorescence decreased, while the membrane permeability and malondialdehyde (MDA) increased. Catalase (CAT) and peroxidase (POD) activities increased under heavy metals stress, but superoxide dismutase (SOD) activities decreased. The magnitude of these Cd- and Zn-induced changes was mitigated by Si-addition at different growth stages. The available Cd concentration increased in the soil but significantly decreased in the shoots, which suggested that Si treatment prevents Cd accumulation through internal mechanisms by limiting Cd2+ uptake by the roots. Overall, the phenomena of Si-mediated alleviation of Cd and excess Zn toxicity in two rice cultivars could be due to the limitation of metal uptake and transport, resulting in an improvement in cell membrane integrity, photosynthetic performance and anti-oxidative enzyme activities after Si treatment.
Highlights
Cadmium (Cd) can accumulate in rice plants through the apoplastic or symplastic pathways in the root system, leading to physiological damage such as stunted plant growth, reduced reproduction, degradation of chlorophyll and inactivation of enzymes [1]
The available Cd concentration increased in the soil but significantly decreased in the shoots, which suggested that Si treatment prevents Cd accumulation through internal mechanisms by limiting Cd2+ uptake by the roots
Zinc (Zn) is an essential element for the health and development of rice, but the presence of excess Zn in soil is associated with highly toxic effects in plants, which leads to the inhibition of seed germination, root development and plant growth [2]
Summary
Cadmium (Cd) can accumulate in rice plants through the apoplastic or symplastic pathways in the root system, leading to physiological damage such as stunted plant growth, reduced reproduction, degradation of chlorophyll and inactivation of enzymes [1]. Zinc (Zn) is an essential element for the health and development of rice, but the presence of excess Zn in soil is associated with highly toxic effects in plants, which leads to the inhibition of seed germination, root development and plant growth [2]. There is mounting evidence that the application of Si to soils can alleviate Cd or Zn toxicity in many plant species, including rice [6,7,8], maize [9], wheat [10]. There is increasing evidence that Si application increases resistance to Cd toxicity via a variety of mechanisms. Nwugo and Huerta [12,13] demonstrated that the positive effect of Si on Cd resistance could be due to the inhibition of Cd uptake in roots and the enhancement of light-use-efficiency in leaves. Nwugo and Huerta, Lin et al and Ma et al [14,15,16]
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