Roles Of Ros, No, Cytoplasm Ca²⁺ And G-protein In The Hr Process Of Wheat To Stripe Rust

Programmed cell death (PCD) is a way of cell's suicide highly organized and regulated by genes within the cell. It is also a mechanism set up in long process of evolution for higher living things to eliminate unwanted cells and harmful organization. Hypersensitive response (HR) often results from incompatible plant-pathogen interactions characterized by killing cells rapidly at and around the site of infection and creating decolourizing and then necrotic lesion. Cells undergoing HR can display cytoplasmic condensation and shrinkage; blebbing of plasma membranes and nuclear membranes; chromatin condensation and marginalization; degradation of nuclear DNA. Therefore HR is considered as a form of PCD. Many studies indicate that the courses of cell's HR are not the harm of pathogen infected the cell, but the expression of defense gene of the cell. Incompatible interaction between wheat and stripe rust shows a typical phenotype of HR. It has an important theoretical and practical meaning to explore the mechanism of this kind of defense.Recent years a great progress has been achieved about how plant regulates its defense system to pathogens. Many evidences prove that reactive oxygen species (ROS), mainly about O₂^·-and H₂O₂, take an important role in plant resistance to pathogens. ROS can attack unsaturated fatty acid within cell's plasma membrane through enzymic and nonezymic ways, activate lipid peroxidation and membrane protein condensation to damage cell's structure and function. On the other hand, ROS acts as a signal molecule to participate defense reaction, cell death and regulation of expression of resistant genes to plant pathogens infection. NO, an important signal molecule in mammalian, has been proved to be a kind of elicitor and plays roles in process of plant development, stomatal closure, wound concrescence, defense to abiotic stress and activation of disease resistance. Plant heterotrimeric G protein, linking G protein-coupled receptor in the outside of membrane and effecter in the inner side of membrane, carries out important physiological functions on signal transduction and biological regulation, including reaction to hormone, drought, light and pathogens; switch of ion channel; cell division; and so on. Calcium is one of the most important second messengers in plants. It conveys signals received at the cell surface to the inside of the cell through spatiotemporal changes in cytosolic free calcium concentrations ([Ca²⁺]cyt) that are decoded by an array of"Ca²⁺ sensors"and regulates plant's growth, developments, defense to stresses.With this study we tried to understand the roles of ROS, NO, [Ca²⁺]cyt and G protein in the defence responses for plants to cope with pathogenic infections. Changes of ROS; NO; activities of enzymes (including SOD, CAT, POD and APX) that are known to detoxify ROS in plant; permeability of cell plasma membrane; changes of [Ca²⁺]cyt and activity of G protein were investigated in the incompatible and compatible interaction systems, Lovrin13/CY29 and Lovrin13/CY25. The research results are as follows:1. ROS burst occurs twice after infection of stripe rust within wheat leaves. Each burst plays important roles in the defense of wheat to stripe rust. Anterior ROS burst, in which H₂O₂ accounts for preponderant proportion, functions as signal molecules to activate cell's defense including HR. Posterior ROS burst, in which O₂^·-makes up the majority, takes roles as toxic substances to kill pathogens and cell itself.2. Glutathione (GSH) increases rapidly after infection of wheat rust in both compatible interaction system and incompatible interaction system. The same concentration is investigated form the two interaction system. Oxidized glutathione (GSSG) gets rapid increase in compatible interaction system after infection of wheat rust, while it gets slight increase in incompatible interaction system. Ratio of GSH/GSSG can be used as an indicator of wheat Lovrin13 resistance to stripe rust. Ratio of 0.2 is the critical value between resistance and susceptibility of wheat to stripe rust. Wheat will show resistant phenotype when the ratio is above 0.2, while wheat will show susceptible phenotype.3. NO plays dual roles in the interaction system of wheat and stripe rust when wheat gets infected with stripe rust. Up on the concentration NO can affect both host and pathogen. Under a suitable concentration NO can directly suppress the growth of pathogen invaded in wheat cells, and on the other hand, it can transport signal to adjoining cells around the infection point to activate HR there. The ratio of NO/ROS can affect host resistant phenotype in the interaction of wheat and stripe rust. Wheat will have resistance to rust when the ratio of NO/ROS is higher than 1.3, while wheat will show susceptibility to rust when the ratio is lower than 1.3. Therefore the relative concentration of NO and ROS takes an important role in wheat and stripe rust interaction system.4. The increase of cytosolic free calcium concentrations is a prerequisite for HR after the infection of stripe rust into cells of wheat leaf. As an internal cellular messenger or second messenger, Ca²⁺ participates the defense of wheat to stripe rust when HR occurs in the interaction between wheat and rust.5. GTP-binding protein, located in the plasma membrane of wheat leaf cells, is activated by avirulent race of stripe rust and transduce the signal intracellular and defense reaction expresses with HR within the infected cell and cells adjacent.