Ultrastructural changes in host leaf cells caused by host-selective toxin of Alternaria alternata from rough lemon

A pathotype of A. alternata with selective pathogenicity to rough lemon produces two or more substances with selective toxicity to the host. The major toxin was extracted from culture fluids with ethyl acetate and purified by several different chromatographic procedures. Toxin (10 ng/mL, 25 μL) was applied to leaves; within 24 h, water congestion and veinal necrosis were evident. The first toxin-induced change detected by electron microscopy was in the mitochondria; toxin at 1 μg/mL caused swelling, reduction in numbers and vesiculation of cristae, and decreases in electron density of the matrix. At 1 h after toxin treatment, the percentages of affected mitochondria in cells of several tissues were 18 in bundle sheaths, 9 in mesophyll cells adjacent to bundle sheath, and 9% in mesophyll cells remote from sheath. The number of affected mitochondria increased with time, until nearly 100% were affected at 6 h. No effects on other organelles were evident at 6 h. No ultrastructural changes were evident in cell...