The Prelimnary Studies On HR Mechanism Of Wheat In Response To The Powdery Mildew Fungal Attack

The cultivar of wheat yang 158 is responds with HR-resistance to powdery mildew isolate Qiu1 and compatible with isolate Bai3. The aim of this research is to understand the mechanism of resistance to powdery mildew in wheat and to analyze the role of reactive oxygen species in plant resistance based on the combination.The histochemical studies revealed that: the development of condium in different interaction types were similar at 6h, 12h, 24h after inoculation, the primary germ tubes of Bgt emerged from the germinating condium, the other part of Bgt formed appressorium germ tube, and condium formed appressorium and wheat cells formed papillae at 6h,12h and 24h after inoculation repectively. At 48h after inoculation with isolate Bai3, the primary hyphae growed from the apex of the appressorium over the surface of the host epidermal cells, and condium developed further into haustoria, at 72h after inoculation. primary hyphae developed into secondary hyphae and formed a hyphal colony with secondary haustoria. The colony began to produced condiophores and condia at 4 days after inoculation. At 48h after inoculation with Qiul, wheat cells producing HR in resistance reaction, and at 96h after inoculation, the cells next to HR cells produced HR.HR cell is able to be detected by using DAB staining or fluorescence microscope, and the accumulation of H₂O₂ in HR cells can be observerd by DAB stainingThe number of HR cells increased in compatible reaction treated with H₂O₂ , but decreased with the treatments of ROS scavengers, such as ascorbic acid, glutathione, catalase . So H₂O₂ was related to HR to Bgt in wheat. As well as the number of HR cells increased in compatible reaction treated with fusicoccin, it can be hypothesized that the activation of H⁺-ATPase is related to HR.To isolate differentially expressed genes among defferent combination of plant/isolation by cDNA-AFLP, more 200 cDNA fragments were observed to specially expressed in resistant leaf but not in susceptible leaf and mock-inoculated leaf. Out of which, total 60 cDNA fragments were cloned and sequenced. By blasting against GenBank databases, 9 cDNA fragments showed high homology to function-identified genes. Expression of the 9 fragments in leaves at 24h after inoculation were annlyzed by RT-PCR: 5 cDNA fragments are specially eapressed in resistant leaf, and 5 fragments encoded: Cu/Zn-superoxide dismutase copper chaperone precursor, putative insulin degrading enzyme, putative Bile acid beta-glucosidase, ribulose-l,5-bisphosphate carboxylase/oxygenase large subunit and a PHD finger family protein. The expression of 2 cDNA fragments which encoded Mla-like protein, CopF Cu-ATPase are stronger inresistant leaf than in susceptible leaf and mock leaf. Other 2 cDNA fragments espressed in all leaves.