Soil heavy-metal pollution leads to excessive heavy metals
in rice
and other food crops, which has caused serious impacts on the ecological
environment and on human health. In recent years, environmental friendly
treatment methods that reduce the bioavailability of heavy metals
in soil by soil microorganisms improving the tolerance of heavy metals
in rice and reducing the transfer of heavy metals from the roots to
the above-ground parts of rice have attracted much attention. This
paper reviews the role and mechanism of soil microorganisms in alleviating
heavy-metal stress in rice at home and abroad in recent years. At
present, microorganisms tolerant to heavy metals mainly include bacteria
and fungi, and their mechanisms include the adsorption of heavy metals
by microorganisms, the secretion of growth-promoting substances (growth
hormone, ACC deaminase, IAA), changing the physical and chemical properties
of the soil and the composition of the microbial community, changing
the transport mode of heavy metals in soil, the improvement of the
antioxidant capacity of rice, etc. Hence, soil microorganisms have
good application value and prospects in rice and other crops. However,
the vast majority of current research focuses on a single strain,
the screening principles of strains are limited, the pathogenicities
of the strains have not been evaluated, and there are still few field
experiments under natural conditions. In the future, we should strengthen
the action of soil microorganisms on rice in response to the above
problems in heavy metals, to better promote the microbial remediation
technology.
Background: Cd is one of the highly toxic heavy metals to most organisms, including humans and plants, and Cd-contaminated rice from China has become a global food safety issue. The early prediction of OsPCR (the plant cadmium resistance protein) which contained a PLAC8 domain was related with the accumulation of Cd in rice. To further understand the biological function of the OsPCR genes on the Cd tolerance and Cd accumulation in rice, we used a low grain-Cd-accumulating rice (xiushui 11) and a high grain-Cd-accumulating rice (xiushui 110) varieties to analyze the relationship between the expression levels of the two most abundant expression genes (OsPCR1 and OsPCR3) and the Cd concentrations in different tissues at different growth periods during Cd stress, and transgenic experiments of OsPCR1 and OsPCR3 were carried out. Results: OsPCR1 and OsPCR3 were closely related with Cd accumulation. Overexpression of OsPCR1 and OsPCR3 could not only increase the Cd tolerance, but also decrease the Cd accumulation obviously in different parts of the transgenic rice plants (especially in the rice grains), while the RNAi expression plants showed the opposite results. Conclusions: These results indicate that OsPCR1 and OsPCR3 play critical roles in Cd accumulation in rice, which provides a theoretical basis for the safe production of rice.
Cadmium (Cd) contamination has been recognized as a major threat to the agricultural system and crop production which posing serious threat to human health. Salicylic acid (SA) serves as an important signaling molecule and plays an important role in against Cd toxicity. In the previous field experiments, we found SA spraying could reduce the Cd accumulation of rice grain grown in Cdcontaminated soil. This study investigated the effects and mechanisms of SA spraying on leaves of rice seedlings under Cd stress. Results showed that SA treatment could alleviate the Cd toxicity of rice not by changing the physical and chemical properties of the soil, but by increasing the activities of antioxidant enzymes to reduce the H 2 O 2 accumulation in rice. And the key factor of SA treatment reducing Cd accumulation in rice grain was the decreasing of Cd contents in rice leaves at the flowering stage. This indicated that SA could modulate the Cd accumulation of shoots to reduce the Cd translocation to rice grain. Furthermore, SA could increase the H 2 O 2 contents in a short-term to activate the SA-signaling pathway, and modulate the expression levels of Cd transporters (OsLCT1 and OsLCD) in rice leaves toraise Cd tolerance and reduce Cd accumulation in rice grain. Thus, SA spraying can be used as an effective measure to cope with Cd contamination in paddy soils. Recently, Cd-contaminated rice has also occurred in China, which poses important public health risks (Liu et al., 2016b). Therefore, it is essential to produce low-Cd rice to reduce the potential risks that
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