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

在感染稻瘟病菌的关口病斑突变体中观察到色氨酸脱羧酶（TDC）和单胺氧化酶（MAO）活性的增加。这些酶活性在M.稻瘟病菌对水稻细胞的影响，即使在Sekiguchi病斑形成后也保持高水平。在病斑形成前接种稻瘟病菌的叶片中观察到TDC基因的光依赖性表达。稻瘟病菌孢子萌发液也能诱导Sekiguchi病斑的形成，并伴随着酶活性的增加和色胺的积累。在光照条件下，用单胺氧化酶底物处理也能诱导Sekiguchi损伤，而用非底物处理则不能诱导Sekiguchi损伤。在MAO抑制剂和H_2O_2清除剂存在下，色胺光依赖性诱导的Sekiguchi损伤被显著抑制。在放线菌酮（CHX）或热（HS）预处理的Sekiguchi病斑突变体叶片中，Sekiguchi病斑的形成和色胺的积累 关于我们 对稻瘟病菌侵染的抑制作用显著。在CHX或HS预处理的叶片中，TDC和MAO活性的光依赖诱导也被显著抑制。光照条件下，接种稻瘟病菌的Sekiguchi病斑突变体叶片中的DNA片段化和DNase活性显著增强。然而，在CHX或HS预处理的叶片中，即使在光照下也没有观察到梯状化或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电泳分析表明，病斑突变体的细胞DNA发生了断裂，表明：1）长波长光激活病斑突变体的色胺途径，2）长波长光（550- 650 nm）抑制病斑突变体的过氧化氢酶活性。（3）Sekiguchi病斑突变体的病斑形成是一种类似于光中毒的反应，其反应是由光依赖的色胺途径激活引起的，而色胺途径是光增强抗性的原因。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