SUPEROXIDE-DISMUTASE AND ARBUSCULAR MYCORRHIZAL FUNGI - RELATIONSHIP BETWEEN THE ISOENZYME PATTERN AND THE COLONIZING FUNGUS

Total activity and the isoenzymatic pattern of superoxide dismutase (S OD; EC 1.15.1.1) were studied at different growth times in the followi ng arbuscular-mycorrhizal (AM) symbioses: Trifolium pratense-Glomus mo sseae, T. pratense-Glomus intraradices, Allium cepa-G. mosseae, and A. cepa-G. intraradices. In nonAM red clover, total SOD activity increas ed two-fold in 50- and in 80-day-old plants, compared to 15- and 30-da y-old plants. However, in plants inoculated with AM fungi, the activit y only rose to the same level after 80 d of growth. In contrast, no ch anges in SOD activity were detected in similar experiments carried out with onion. The results obtained from red clover are discussed in ter ms of a possible shift in the plant roots from control growth conditio ns to a senescent stage. Analysis of SOD isozymes in the symbioses stu died showed the presence of one Mn-SOD and two CuZn-SODs (CuZn-SOD I a nd CuZn-SOD II) in each plant species at 15 d of growth. In both red c lover and onion, two new CuZn-SODs (named CuZn-SOD 1 and CuZn-SOD 2) w ere detected in tissues older than 30 d, besides the constitutive isoz ymes indicated above. Both T, pratense-G. mosseae, and A. cepa-G. moss eae symbioses also expressed a specific isozyme (mycCuZn-SOD), which w as absent in the symbioses with G. intraradices. The expression of myc CuZn-SOD could only be detected in material older than 30 d. The funga l origin of this isozyme is discussed in terms of its specificity in t he symbioses of plants with G, mosseae.