Chromatin structure variation in successful and unsuccessful arbuscular mycorrhizas of pea

Summary Lincoln and Frisson varieties of endomycorrhiza-forming pea plants and isogenic mycorrhiza-resistant Frisson mutant (P2) plants were inoculated withGlomus mosseae. Nuclei released from inoculated and non-inoculated (control) roots were analysed for chromatin structure and activity using flow cytometric techniques. Chromatin accessibility to the specific DNA fluorochrome DAPI at saturating and non-saturating concentrations was measured. DNA fluorescence of nuclei of mycorrhizal Lincoln and wild genotype Frisson plants was significantly increased, compared 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 uninoculated controls. Nuclei released from mycorrhiza-infected Lincoln roots were more sensitive to DNase I than those of uninfected ones. These results indicate a dramatic increase in that portion of the genome which can be transcribed in response to AM infection.Abbreviations AM arbuscular mycorrhizas - CRBCs chicken red blood cells - CV coefficient of variation - DAPI 4 6-diamidino-2-phenylindole - DNase I deoxyribonuclease I - EDTA ethylenediamine tetraacetic acid - FCM flow cytometry - TMN Tris MgCl₂ NaCl buffer