ICOM1 Abstract

talk session 5 BERTA, GRAZIELLA1, GUIDO LINGUA1, ANNA FUSCONI2, ANTONIO TROTTA2. 1Dipartimento di Scienze e Tecnologie Avanzate, corso Borsalino 54, 15100, Alessandria, Italy. 2Dipartimento di Biologia Vegetale, Viale Mattioli 25, 10125, Torino, Italy. Quantitative and structural variations in host cell nuclei of arbuscular mycorrhizal and/or pathogenic systems. Some evidence exists that arbuscular mycorrhizas (AM) increase tolerance of host plants to soil-born fungal root pathogens. A strong protective effect has been shown in tomato (Lycopersicon esculentum) against Phytophthora nicotianae v. parasitica, resulting in a significant reduction of plant growth inhibition and of necrotic root zones. We investigated quantitative and structural nuclear variations induced in tomato roots by Glomus mosseae, by P. nicotianae v. parasitica, and by their interactions, using a combination of transmission electron microscopy (TEM), flow cytometry and cytochemical techniques. Nuclei extracted from tomato roots of mycorrhizal and control plants (forty- five days old), infected and uninfected by the pathogen, were analysed by flow cytometry after staining with saturating DAPI concentration (DNA quantity), or with under-saturating DAPI or saturating propidium iodide (PI) (chromatin structure). Saturating DAPI staining caused higher fluorescence in control and mycorrhizal root nuclei compared to those extracted from P. n. v. parasitica inoculated roots, suggesting DNA loss in the latter. Undersaturating DAPI and saturating PI staining of non-mycorrhizal P. n. v. parasitica inoculated plants gave lowest fluorescence, while mycorrhizal plants, both with and without P. n. v. parasitica, had the highest ones. TEM analyses confirmed this pathogen effect on chromatin condensation, which was attenuated by AM. Finally, both saturating DAPI and PI staining gave a peak corresponding to a 4C nucleus population, and the ratio of number of 4C nuclei to 2C nuclei was always significantly higher in non-mycorrhizal plants. These last results are particularly intriguing and suggest that in tomato, AM fungi could interfere with DNA endoreduplication processes.