Symbiosis-stimulated chitinase isoenzymes of soybean (Glycine max (L.) Merr.)

and to be colonized by arbuscular mycorrhiza (AM) fungi (Harrison, 1997). Often, nodule formation by a Isoforms of endochitinase in soybean were studied in given bacterial strain is restricted to only a few host plant relation to root symbiosis. Five selected cultivars difgenera, and varieties of a given legume species may differ fering in their nodulation potential were inoculated in nodule formation when inoculated with a given strain. with two strains of Bradyrhizobium japonicum, the Specifically in soybean, allelic genes have been described broad host-range Rhizobium sp. NGR234, and with the which restrict nodulation of certain genotypes by certain mycorrhizal fungus Glomus mosseae. Total chitinase Bradyrhizobium strains (Vest, 1970; Qian et al., 1996). activity in nodules was up to 7-fold higher than in Other, ‘broad host-range’ rhizobia exist: Rhizobium sp. uninoculated roots and in mycorrhizal roots. The chiNGR234 is such an example, and it is able to induce tinase activity in nodules varied depending on the nodules on more than 110 genera of legumes as well strain–cultivar combination. On semi-native polyacrylas the non-legume Parasponia (SG Pueppke and amide gels, four acidic isoforms were identified. Two WJ Broughton, unpublished results). During the infection isoforms (CH 2 and CH 4) were constitutively present process, plants secrete flavonoids and isoflavonoids which in all analysed tissues. The other two isoforms (CH 1 and CH 3) were strongly induced in nodules and were induce bacterial nodulation genes. Most of these genes stimulated in mycorrhizal roots as compared to uninare involved in the synthesis of Nod factors, a family of oculated roots. The induction of CH 1 varied in nodules lipo-chitooligosaccharide signal molecules. Nod factors depending on the soybean cultivar. This isoform was stimulate various responses in the host plants, including also stimulated in uninfected roots when they were root hair deformation, induction of early nodulins, and treated with tri-iodobenzoic acid, rhizobial lipoformation of nodule primordia (Dénarié et al., 1996; chitooligosaccharides (Nod factors) and chitotetraose. Long, 1996; Schultze and Kondorosi, 1996). CH 3 was not affected by these stimuli indicating that In contrast to rhizobia, AM fungi usually have a this isoform could represent a marker for enzymes ‘broad host-range’: i.e. a given species can usually form induced in later stages of the symbiotic interactions. mycorrhizal roots with many different angiosperm families. Several similarities have been reported between the