| It is now generally assumed that the symbiosis between arbuscular mycorrhizal (AM) fungi and roots results in an increase in resistance of plants to soil-borne pathogens. Previous works on the interactions between plant, AM fungus and soil-borne pathogen conferred the bioprotection role of AM fungi, especially when plants were mycorrhized before pathogen infection. However, little is known about the mechanisms involved in AM-bioprotection. In this thesis, a series of studies have been conducted on Vitis amurensis and soybean cultivars 'Shuangyou' and 'Ludou 4'which are respectively susceptible to root knot nematode (RKN, Meloidogyne incognita) race 3 and soybean cyst nematode (SCN, Heterodera glycines) race 4 in order to understand the mechanisms involved in the plant's resistant or tolerant response induced by AM fungi towards nematode, and investigate whether the elicitation of pathogenesis-related (PR) protein gene is associated with the induced systemic resistance (ISR) by AM fungi and what signal molecule directly activate the expression of the PR protein gene. The main results are as follows:1. The colonization percent of AM fungi and penetration rate of nematode, as well as the activities of peroxidase (POD), phenylalanine ammonia lyase (PAL), 3 -1 , 3-glucanase and chitinase in plant roots inoculation with AM fungi and /or nematode were determined. Infection with M.incognita race 3 and H. glycines race 4 did not significantly decrease the colonization percent of AM fungi, while inoculation with AM fungi significantly decrease the penetration rate of" nematode. AM fungi induced the increase of the activities of peroxidase(POD), phenylalanine ammonia lyase(PAL), P -1 , 3-glucanase and chitinase in both grape and soybean roots. Furthermore, the peaks of the activities of POD. PAL and chitinase in plant roots pre-inoculated with AM fungi and post-infected with nematode appeared while the colonization percent of AM fungi increased and the penetration rate of nematode decreased rapidly, indicating that these three enzymes play important roles in the mechanisms of resistant response induced by AM fungi against nematode and chitir.be more important. However, the role of P-l, 3-glucanase in the protection induced by AM fungi from infection of nematode was not obvious.2. The analysis of PAL5 and chitinase Chibl and VCH3 mRNA levels in plant roots inoculation with AM fungi and/or nematode using Northern-Blot and relative quantitative RT-PCR (RQRT-PCR) indicated that the defense genes, PALS and PR protein (chitinase) genes CTi/bl and VCH3, were regulated at transcriptional level by AM fungi and the elicitation of the pathogenesis-related (PR) protein gene was associated with the induced systemic resistance (ISR) by AM fungi. The dynamic changes in expression of PAL5 and chitinase Chib\ and VCH3 mRNA was very similar to that of the corresponding enzyme activities. Moreover, AM fungi could enhance the expression of defense genes during the nematode-resisting. The higher level of the three genes mRNAs were observed in plant roots pre-inoculated with AM fungi and post-infected with nematode than that in plant roots only infected with nematode, thus the pre-activation of defense response by AM fungi can pre-dispose the plant roots to react more fast to the second infection (nematode), and increase the ability of plant in nematode-resisting.3. The High Performance Capillary Electrophoresis (HPCE) was performed to assay the content of SA in plant roots inoculation with AM fungi and /or RKN, and the results showed that inoculation with AM fungi enhanced the level of SA content (about 10-folds above CK) in grape roots. Furthermore, at each time point, the amount of SA in plant roots of pre-inoculated with AM fungi and post-infected with RKN was greatest (about 10-16 folds equal to that of CK). Also, it is noteworthy that the peak of SA content appeared earlier than that of the activity of chitinase and the expression of chitinase mRNA, suggesting that SA might involve the ISR signal... |
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