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Role of Light and Malate in the Decreased Sensitivity of cms-T Cytoplasm Maize Leaves to Bipolaris maydis Race T Toxin

Leaf segments from Texas male sterile (cms-T) cytoplasm maize isolines exposed to light (50 μM s^-1 m^-2) for 8 h or more before or after being infiltrated with the Bipolaris maydis race T toxin (T-toxin) leaked significantly less electrolytes when immersed in distilled water (DW) for 24 to 48 h than did dark-treated leaf segments. No comparable effect of light on toxin-induced electrolyte leakage was observed with normal (N) cytoplasm isolines. Toxin-treated cms-T leaf segments incubated in DW for three consecutive 12-h periods of alternating light and dark showed significantly greater electrolyte leakage than leaf segments incubated in continuous light for 36 h and significantly less leakage than segments incubated in continuous dark for 36 h.Exposure of cms-T, but not N, cytoplasm leaves to 25 or 50 μM malic acid decreased their sensitivity to T-toxin in the dark to a level similar to that observed when leaves were incubated in the light without malic acid. The potency of T-toxin appeared to be unaffected by its exposure to light. The loss of electrolytes from T-toxin-treated cms-T cytoplasm leaf segments was at approximately the level seen with light or malate when 25 μM H₂O₂ was added to the DW bathing solution. Evaluation of the data points to the possibility that H₂O₂ might be involved with the altered sensitivity of cms-T cytoplasm leaves to T-toxin caused by either light or malate.