Histochemiacal Studies On The Roles Of Cytoskeleton In The Nonhost Resistance Of Cucumber To Blumeria Graminis F. Sp. Tritici

Histochemical methods were utilized to investigate the accumulation of H₂O₂, thegeneration of hypersensitive response and the deposition of papillae in the nonhost interactionof cucumber and Blumeria graminis f. sp. tritici （Bgt） and incompatible host interaction ofwheat to bgt. Besides, cucumber cotyledons were treated with actin inhibitor CA beforeinoculation with bgt to investigate the main defense responses at specific time points. Thisresearch studied the mechanisms of nonhost resistance of cucumber to Bgt and the role ofactin cytoskeleton in the nonhost resistance of cucumber against Bgt at the histochemicallevel. The results are as below:1. After the staining and clearing of the leaves, percentage of condium germination wascalculated on nonhost cucumber and host wheat. The results show that the germination ofbgt had a significant difference at6hours after inoculation （hai）. As the incubation timeextended, the germination rates in both interactions constantly increased and reachedabove80%at24hai, with no significant difference.2. The staining of DAB, trypan blue and coomassie bright blue was applied in theobservation of the frequencies of H₂O₂deposition, HR generation and papilla formationon nonhost cucumber and host wheat. The results show that the occurrence of H₂O₂wasearlier and the maximum incidence of H₂O₂generation was higher, and the incidence ofHR production was higher in nonhost at all time points, indicating that H₂O₂accumulationand HR generation are the main defense reactions of cucumber resistance to bgtpenetration and play pivotal roles in the NHR of cucumber. H₂O₂deposition and HRproduction accompanied with papilla accumulation was observed, denoting papillaformation is related to the production of H₂O₂and HR.3. The frequency of haustorium formation in nonhost cucumber is far lower than that in hostwheat, and the haustorium formation in nonhost stays at the stage of haustorium initial.Haustorium initials could scarcely further developed and secondary hyphae could not beobserved in host wheat, suggesting that NHR of cucumber is important in restraining theformation of haustoria and preventing the penetration of bgt. 4. Germination of bgt on cucumber cotyledons was detected after treatment with CA. It wasfound that the germination rate of conidia in CA treatment was slightly higher than incontrol and the difference in germination rate was not obvious. At24hai, germinationratios of bgt in both treatments were above90%.5. After treatment with CA, the generation of H₂O₂, HR and papillae were all suppressed.The percentage of H₂O₂accumulation was lower in CA treatment at every time point. Thestaining of HR was lighter, and papillae was smaller and looser in CA treatment than incontrol.6. The incidence of haustorium formation was calculated in cucumber with CA treatment,showing that the generation of haustoria reduced at the early stage of incubation. As theincubation time extended, the percentage of haustorium formation was evidently higher inCA treatment than in control at later stage, indicating the depolymerization of actincytoskeleton promotes the penetration of bgt. Our study reveals that cytoskeleton playsvital roles in NHR of cucumber.