| Resistance of 12 different Arabidopsis ecotypes and genetypes to some important fungal pathogens were studied, and different ecotypes which were different resistance to the same pathogen had been obtained. The molecular mechanisms of resistance and expression of defense-related genes after inoculation were also studied in this paper.All the 12 Arabidopsis ecotypes tested were incompatible to Fusarium campestris, F. oxysporum f.sp.niveum, Setosphaeria turcica and Erysiphe cichoracearum. Some ecotypes were compatible to Alternaria brassicicola, Botrytis cinerea (two strains), Phytophthora infestans and Peronospora parasitica. Among them Col was compatible to B. cinerea and P. parasitica, C24 was compatible to P. parasitica, NahG was compatible to B. cinerea. Est-1, Bay-0 were incompatible to A. brassicicola, B. cinerea, P. infestans and P. parasitica. The application of SA or JA to Est-1 and Bay-0 plants enhanced resistance to P. infestans.To study roles of defensive enzymes in the host resistance, their activities were analyzed in inoculated and uninoculated plants. The results indicated that PAL, POD and PPO activities were induced in inoculated plants, the resistant ecotype Col usually exhibited a quicker and higher increase in the activity of these enzymes than susceptible ecotypes. The changes of SOD activity followed the process: the activity of resistant ecotype Col showed first a little increase then a slow decrease and another swift increase, reach the highest value in the seventh day after inoculation, and finally decreased again in the ninth day after inoculation. As compared with susceptible ecotypes Est-1 and Bay-0, SOD activity increased quickly in seven days after inoculation and dropped down in the ninth day after inoculation. The CAT activity of Col, Est-1 and Bay-0 ecotypes also showed a change after infection with P. infestans spores. The CAT activity in Col kept increasing until reaching the highest level in the seventh day and then dropped slowly. As to CAT activity in ecotypes Est-1 and Bay-0, there were no any change during the first day after inoculation but increased gradually after and reached the maximum level after 3-5days. The maximum value of CAT in the resistant ecotype Col was higher than in the susceptible ecotypes Est-1 and Bay-0.Other non-enzyme substances which related to resistance were also observed after inoculation with P. infestans. It was found that : (1)The change of susceptible host cell membrane permeability occurred usually earlier and a wider range compared with resistant ecotypes. (2) MDA which is generated from peroxidized membrane lipid, increased in all three ecotypes used. The increase of MDA in Col after inoculation occurred usually earlier but the maximum value was lower while compared with Est-1 and Bay-0 ecotypes.DDRT-PCR method was optimal to study the differential gene expression between inoculated and uninoculated plants of Col, Est-1 and Bay-0, and total 108 differentially expressed cDNA fragments were found. Among them 57 cDNA fragments were found to hybridize to cDNA from inoculation and uninoculation plants. Four of the differentially expressed cDNA fragments were cloned and sequenced. Their lengths were 269bp and 466bp, respectively. The fragment 7-6 (466bp) was derived from gene which encodes a member of the 1-aminocyclopropane-l-carboxylate synthase. 6-6(269bp) was derived from gene At5g32405.1 which the function was unknown.Reverse Northern blotting method was exploited to study the expression of the pathogen-induced resistant genes. It was shown that the product of second PCR amplification of Col plants displayed a positive reaction to PR-3. Bay-0 displayed positive reaction to PR-1. Est-1 displayed positive reaction to At2g32680, At1g67980, PDF 1.2, PR-3 and PR-4. Both reverse Northern blotting and DDRT-PCR were used to study the expression of defense-related genes in inoculated and uninoculated Arabidopsis plants. SA induced expression of At2g32680, Atlg67980 and PR-1 in Bay-0 plants. PDF1.2 was induced after treatment by JA in Col plan...
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