Physiological And Genetic Analysis Of Lesion Mimic Mutant In Soybean

In the long evolutionary process, plants gradually formed a very complex defensemechanism to resist the infection of pathogens, and one of the most effective types ishypersensitivity (hypersensitive response, HR). By the pathogen infection of pathogen, the infectedand surrounding cells rapidly apoptosis, form necrotic spots in a certain area to curb the furtherspread of pathogens, known as hypersensitivity.While without the infection of pathogen or obvious injury,adversity stress, some plants canspontaneously form spots similar to the necrotic spots formed by the infection of pathogen,known as lesion mimic mutant. The formation of lesion may be caused by a variety of reasons,such as programmed cell death and the imbalance of plant metabolic pathways such assphingolipids substances and chlorophyll.In addition, the formation of necrotic spots in a large part of lesion mimic mutants is formedby the accumulation of reactive oxygen species. Reactive oxygen species are kinds of oxygenmetabolites with high chemical activity, mainly include superoxide (O₂^－), hydrogenperoxide(H₂O₂), and hydroxyl radicals(OH-). Low concentration of reactive oxygen can triggerplant defense responses, while high levels of reactive oxygen species can result in the death ofplant cells. The generation and clearing mechanisms of reactive oxygen species form a complexnetwork. Nonenzymatic antioxidants include the major cellular redox buffers ascorbate,glutathione (GSH), tocopherol, flavonoids, alkaloids, andcarotenoids, while enzymatic reactiveoxygen species scavenging mechanism sinplants include superoxide dismutase (SOD), ascorbateperoxidase (APX), peroxidase(POD), and catalase (CAT).This paper preliminary analysises lesion mimic mutant physiologically and genetically,which was obtained from Hedou12by γ-radiation. The main conclusions are as follows:1The lesion mimic mutant began to turn yellow and exhibited yellow-brown necroticspots just after euphylla unfolded. The necrotic spots spreaded and finally killed plants.Compared to wild types, mutants were significantly short and thin. Chlorophyll content andphotosynthesis in mutant were also lower. 2The staining of Trypan Blue showed that cells at the necrotic spots died.Semi-quantitative PCR also indicated that the expression of pathogen genes as PR1, PR4, PR10were increased in mutant, while PR2, PR6, PDF1.2were decreased. The results indicated thatsystemic acquired resistance was already started.3In the mutant especially at the necrotic spots, the degree of membrane lipidsuperoxidation was aggravated, and the content of MDA was increased in mutant. The stainingof DAB showed that H₂O₂deposited at the necrotic spots. Besides, reactive oxygenscavenging enzymes such as POD, CAT were all stimulate in mutant. But SOD was restrainedin mutant, semi-quantitative PCR also indicated that the expression of CSD1,CSD2,FSD weredecreased. SOD can catalyze O2－to generate O2and H₂O₂, and H₂O₂was decomposed byPOD, CAT, APX. Then we can conjecture that the misregulation of the ROS metabolism maybethe the reason of cell death.4The genetic analysis suggested that this lesion mimic mutant was a homozygousrecessive mutant. We hybridized mutant and William82and obtained F2mapping population.The location of lesion mimic gene is undergoing.5The methyl halide is biosynthesized by the enzymatic reaction of methyl chloridetransferase (MCT). We obtained transformants of overexpression of MCT of soybean byparticle bombardment. This paper has some practical significance of plants for preventingnematodes.