Mikio Nozu

Primary Effect of a Host-Selective Toxin From Magnaporthe Grisea to Mitochondria of Rice Leaves

The effects of the toxin produced by the rice blast fungus Magnaporthe grisea on host (rice and barley) and non-host (finger millet) plants were examined by ultrastructural observation and morphometric measurement. The first toxin-induced changes in rice and barley plants were the loss of the mitochondrial matrix and the disruption of mitochondrial cristae. These modifications in mitochondria were observed 1 hr after toxin exposure and the frequency of modified mitochondria did not increase with time after toxin treatment. Morphological and ultrastructural changes were not observed in other organelles. Toxin effects were observed in epidermal, mesophyll and phloem cells of barley and rice but not in leaves of the non-host plant, finger millet. Further, mitochondrial modifications were observed in epidermal cells of rice cv. Asahi 12 hr after inoculation of M. grisea spores. These results indicated that mitochondrial modification induced by the toxin was a host-specific phenomenon and possibly an essential event for M. grisea to establish basic compatibility with host plants at the species level.