Effects of Helminlhosporium maydis race T toxin on protoplasts of resistant and susceptible coro (Zea mays)

Leafprotoplasls from resistant (N, e, and S cytoplasm)and susceptible (T cytoplasrn)com inbred W182B (Zca mays L.)exhibited a differential response after exposure to Helminthosporium maydis race T toxin. The volume of untrealed protoplasts jncreased twofold during the first 24 h after isolation and by 48-72 h, most protoplasts exhibited an extensive network of cytoplasmic strands and the chloroplasts were distributed throughout the cytoplasm by cyclosis. However, susceptible protoplasts exposed to ~2 ¡.t..g toxin/rnl failed to increase in volume and cytoplasmic !'treaming was rarely observed. By 72 h there was exlensive degradation and collapse of susceptible protoplasts exposed to toxin. ResiSlant protoplasts exposed to up to 100 ¡.Lg toxin/mI exhibited a twofold volume increase and were indistinguishable from untrealed protoplasts. Susceptible protoplasts exposed to 0.1 ¡.Lg toxin/mI aJso appeared unalTected, bUI at 1.0 ~ toxio/ml an intermediate re;-¡ponse was observed. The differential response to H. múydis mce T loxin of protoplasts from resistant and susceptible com correlates wel..l with those effects observed in iotact plant tissues and may serve 10 explain furtherthe mode ofaction ofthe toxinon susceptible com cells.