Molecular elucidation of hypersensitive cell death in lesion mimic mutants of rice infected with Magnaporthe grisea.

侵染Mgrisea的Sekiguchi皮损突变体的色氨酸脱羧酶(TDC)和单胺氧化酶(MAO)活性升高。这些酶的活性在稻瘟病菌侵入水稻细胞之前就已观察到，并在关口病斑形成后仍保持较高水平。在接种稻瘟病菌的叶片中，TDC基因的光依赖性表达发生在Sekiguchi病变形成之前。稻瘟病菌孢子萌发液还诱导了关口病斑的形成，并伴有酶活性的增加和色胺的积累。光下有底物的MAO处理也能引起关口损伤，而光下无底物处理不能引起这种损伤。在MAO抑制剂和H_2O_2清除剂存在下，色胺对光依赖的关口损伤有明显的抑制作用。在放线菌亚胺(CHX)或热(HS)预处理的叶中，关口病斑的形成和色胺…的积累更多地受到稻瘟病菌侵染的显着抑制。在CHX或HS处理的叶片中，TDC和MAO活性的光诱导也受到显著抑制。在光照条件下，接种稻瘟菌的关口病斑突变体叶片的DNA片段化和DNA酶活性显著增加。在CHX或HS处理的叶片中，即使在光照下也没有观察到梯形和DNA酶活性。末端脱氧核苷酸转移酶介导的dUTP-Nic末端标记染色和凝胶分析表明，赤口病叶片组织细胞中的DNA片段化。这些数据表明：1)关口病斑突变体中的色胺途径被长波光激活，2)长波长(550-650 nm)光照射抑制稻瘟病菌病斑突变体的过氧化氢酶活性，H_2O_2的产生和积累激活色胺途径，3)关口病斑突变体中的色胺损伤形成是一种类凋亡反应，其反应是由光激活色胺途径引起的，这是光增强抗性的机制之一。较少

Increased tryptohan decarboxylase(TDC) and monoamine oxidase(MAO) activities were observed in Sekiguchi lesion mutant infected with Mgrisea. These enzyme activities were observed before the penetration of M. grisea to rice cells and maintained high levels even after Sekiguchi lesion formation. Light-dependent expression of TDC gene was observed in leaves inoculated with M.grisea before Sekiguchi lesion formation. Spore germination fluid of M grisea also induced Sekiguchi lesion formation accompanied by increased enzymes activities and tryptamine accumulation. Sekiguchi lesion was also induced by treatments with substrates for MAO under light, but not induced by non-substrates under light. Light-dependent induction of Sekiguchi lesion by tryptamine was significantly inhibited in the presence of MAO inhibitors and H_2O_2-scavengers. In cycloheximide(CHX)- or heat (HS)-pre-treated leaves of the Sekiguchi lesion mutant, the formation of Sekiguchi lesions and the accumulation of tryptamine … More by M.grisea infection were significantly inhibited. In the CHX- or HS-pre-treated leaves, light-dependent induction of both TDC and MAO activities was also significantly inhibited. DNA fragmentation and DNase activity were significantly induced in leaves of the Sekiguchi lesion mutant inoculated with M.grisea under light. In the CHX- or HS-pre-treated leaves, however, neither laddering nor DNase activity was observed even under light. Terminal deoxynucleotidyl transferase-mediated dUTP-nic end labeling staining and gel analysis indicated DNA fragmentation in cells of leaf tissues with Sekiguchi lesions.These data show that : 1)Tryptamine pathway in the Sekiguchi lesion mutants is activated by light of long wavelength, 2)Catalase activity is inhibited by light irradiation of long wavelengths (550-650nm) in sekiguchi lesion mutant inoculated with M. grisea, and tryptamine pathway was activated by H_2O_2 generation and accumulation, 3)Sekiguchi lesion formation in the Sekiguchi lesion mutants is an apoptosis-like response and that its response is induced by light-dependent activation of the tryptamine pathway, which is responsible for light-enhanced resistance. Less