CHROMATIN STRUCTURE VARIATION IN SUCCESSFUL AND UNSUCCESSFUL ARBUSCULAR MYCORRHIZAS OF PEA

Lincoln and Frisson varieties of endomycorrhiza-forming pea plants and isogenic mycorrhiza-resistant Frisson mutant (P2) plants were inocula ted with Glomus mosseae. Nuclei released from inoculated and non-inocu lated (control) roots were analysed for chromatin structure and activi ty using flow cytometric techniques. Chromatin accessibility to the sp ecific DNA fluorochrome DAPI at saturating and non-saturating concentr ations was measured. DNA fluorescence of nuclei of mycorrhizal Lincoln and wild genotype Frisson plants was significantly increased, compare d to the controls, at saturating and, more strongly, at non-saturating DAPI concentrations. In contrast, the nuclei of inoculated P2 mutant roots showed a much lower increase in fluorescence, compared to uninoc ulated controls. Nuclei released from mycorrhiza-infected Lincoln root s were more sensitive to DNase I than those of uninfected ones. These results indicate a dramatic increase in that portion of the genome whi ch can be transcribed in response to AM infection.