No abstract

mycorrhizal maize roots could be mimicked by IBA applied Inoculation of maize (Zea mays L.) with the arbuscular mycorrhizal (AM) fungus Glomus intraradices resulted in a exogenously to non-mycorrhizal roots. Addition of trifluorodistinct root phenotype ca 10 days after inoculation. Al-IBA (TFIBA), an inhibitor of IBA-induced root growth and lateral root induction, simultaneously with IBA resulted in a though the fresh weight of inoculated and control roots was phenotype resembling that of untreated controls. In roots about the same, the AM-inoculated roots showed a signifitreated with TFIBA the inoculation with AM fungi did not cant increase in the percentage of lateral fine roots. This increase the formation of fine roots. The TFIBA treatment increase coincided with an increase in free indole-3-butyric acid (IBA) as well as an increase in IBA synthesis. At later also reduced endogenous free IBA and the AM infection rate time points (31 days after inoculation), the free IBA content in mycorrhizal roots. The results are discussed with respect was not increased in infected roots; however, the fraction of to a possible role of IBA in the establishment of AM symbiosis. bound IBA increased compared to controls. The phenotype of are involved in signalling events between AM fungi and host plants. The levels of phytohormones in maize colonized with a Glomus isolate were analysed by ELISA and conventional bioassays (Danneberg et al. 1992, Esch et al. 1994. Measurements of abscisic acid (ABA) showed considerably higher levels of ABA in AM-colonized than in control roots, whereas the concentrations of zeatin riboside (with the exception of later stages of AM development) and indole-3acetic acid (IAA) were similar for infected and non-infected roots (Danneberg et al. 1992). The concentration of ABA in hyphae of Glomus was at least one order of magnitude higher than that in maize roots without AM fungi (Esch et al. 1994). The authors concluded that Glomus is able to contribute to the increase in ABA in the infected roots.Since stable isotope labelled standards became available for the determination of plant hormones, it is possible to measure accurately auxin levels using gas chromatographymass spectrometry (Cohen et al. 1986, Sutter and Cohen

No abstract

Under defined laboratory conditions it was shown that two glucosinolate-containing plant species, Tropaeolum majus and Carica papaya, were colonized by arbuscular mycorrhizal (AM) fungi, whereas it was not possible to detect AM fungal structures in other glucosinolate-containing plants (including several Brassicaceae). Benzylglucosinolate was present in all of the T. majus cultivars and in C. papaya it was the major glucosinolate. 2-Phenylethylglucosinolate was found in most of the non-host plants tested. Its absence in the AM host plants indicates a possible role for the isothiocyanate produced from its myrosinase-catalysed hydrolysis as a general AM inhibitory factor in non-host plants. The results suggest that some of the indole glucosinolates might also be involved in preventing AM formation in some of the species. In all plants tested, both AM hosts and non-hosts, the glucosinolate pattern was altered after inoculation with one of three different AM fungi (Glomus mosseae, Glomus intraradices and Gigaspora rosea), indicating signals between AM fungi and plants even before root colonization. The glucosinolate induction was not specifically dependent on the AM fungus. A time-course study in T. majus showed that glucosinolate induction was present during all stages of mycorrhizal colonization.

The role of arbuscular mycorrhizal (AM) fungi in assisting their host plant in nitrate assimilation was studied. With polymerase chain reaction technology, part of the gene coding for the nitrate reductase (NR) apoprotein from either the AM fungus Glomus intraradices or from maize was specifically amplified and subsequently cloned and sequenced. Northern (RNA) blot analysis with these probes indicated that the mRNA level of the maize gene was lower in roots and shoots of mycorrhizal plants than in noncolonized controls, whereas the fungal gene was transcribed in roots of AM plants. The specific NR activity of leaves was significantly lower in AM-colonized maize than in the controls. Nitrite formation catalyzed by NR was mainly NADPH-dependent in roots of AM-colonized plants but not in those of the controls, which is consistent with the fact that NRs of fungi preferentially utilize NADPH as reductant. The fungal NR mRNA was detected in arbuscules but not in vesicles by in situ RNA hybridization experiments. This appears to be the first demonstration of differential formation of transcripts of a gene coding for the same function in both symbiotic partners.