Silicon-mediated Plant Disease Resistance：Current Knowledge and Perspectives

Although silicon (Si) has not been recognized as an essential element for plant growth, its beneficial effects have been demonstrated for a wide variety of plant species under abiotic and biotic stress conditions. Silicon can increase the resistance of plant disease, such as rice blast, rice sheath blight, rice bacterial leaf blight, rice brown spot, powdery mildew, root rot, rust disease and so on. In regard to mechanisms of silicon-mediated plant resistance to pathogen, several different mechanisms have been proposed. The first hypothesis proposed is mechanical or physical barrier, which claims that silicon application leads to more intensive cell silicification, as well as the formation of cuticle-Si double layer and papilla on rice leaf epidermis cells thus impeding pathogen penetration. However, subsequent studies show that the physical barrier mechanism is not the sole mechanism, and an additional biochemical mechanism exists. This novel mechanism supports that silicon application induced more phytoalexins accumulation in plant epidermal cells. Meanwhile, it is found that silicon application enhanced the activities of peroxidase, polyphenoloxidase and chitinase. It is concluded that silicon plays an active and complex role in mediating plant resistance to pathogen. With the development of molecular technique, more studies involve using gene microarray to analyze the interaction of silicon application and pathogen inoculation on the transcriptional profile of plant. It seems to suggest that Si-treated plants react in response to pathogen inoculation through the up-regulation of defense- and pathogenesis-related genes. However, further studies are needed for exploring the detailed mechanisms by which Si mediates plant stress-signaling transduction.