Ultrastructural effects of Helminthosporium maydis race T toxin on isolated corn mitochondria and mitochondria within corn protoplasts

Abstract

Mitochondria isolated from Texas male-sterile cytoplasm (T) corn roots and mitochondria within T protoplasts showed similar ultrastructural changes after treatment with Helminthosporium (Bipolaris) maydis race T (HmT) toxin. These changes included loss of matrix density, disruption of cristae, and swelling. Damage was observed in isolated T mitochondria after 1-min treatments and in mitochondria within T protoplasts after 5-min treatments. At low toxin concentrations or short treatment times, some mitochondria in isolated preparations and in individual protoplasts were altered whereas others were not. With increases in treatment time or toxin concentrations, all mitochondria were damaged. N cytoplasm mitochondria were unaffected by much higher toxin concentrations and longer treatment times. No ultrastructural effects of HmT toxin on other cytoplasmic components were observed, indicating that mitochondria are structurally affected before other cellular sites. The results support the hypothesis that mitochondria are the primary site of HmT toxin damage in living cells.