GLOMUS INTRARADICES COLONIZATION REGULATES GENE-EXPRESSION IN TOBACCOROOTS

Mycorrhizae are the structural unit resulting from the symbiotic inter action between soil fungi and plant roots, and are accompanied by cons iderable alteration of the metabolism of both partners. In this study changes in the gene expression of Glomus intraradices inoculated tobac co roots were detected following the application of the plant defense chemical activators 2,6-dichloroisonicotinic acid (INA) or (1,2,3)-thi adiazole-7-carbothioic acid S-methyl ester (RTH). In response to mycor rhizal fungal colonization, mRNA steady state level of the pathogen-re lated protein la (PR-la) and the protein accumulation of PR-la and bas ic chitinase were reduced. The suppression of PR-la and basic chitinas e coincided with a significant increase in the level of Zeatin ribosid e (ZR)-like cytokinin compounds in mycorrhizal roots compared to non-m ycorrhizal controls. Application of kinetin and 6-benzylaminopurine (B AP) mixture at 10(-5) M each, to tobacco leaves resulted in a signific ant reduction in PR-1a and basic chitinase protein levels. The possibl e link between the altered expression of these specific plant genes an d the elevated cytokinin level in AM fungus-colonized plants is discus sed.