Effects of monocerin on cell cycle progression in maize root meristems synchronized with aphidicolin.

Monocerin is a benzopyran fungal toxin with broad activity on plants, fungi and insects. Its effect upon cell cycle progression has been analyzed in maize roots. Meristematic cells were synchronized by treatment with aphidicolin. Flow cytometric DNA analysis and mitotic indices indicated durations of 1.5 h, 5 h, 2 h and 1 h for respectively G1, S, G2 and M phases of the normal cell cycle at 25°C. Treatment of these synchronized meristems with 0.5 mM monocerin during release after an aphidicolin block produced a short delay in S phase and then a more important delay (about 2.5 h) in entry into mitosis. Treatments for similar durations (3 h) during progression through the cycle revealed two periods of action of monocerin. The first appears to be mid to late S and the second one G2, before the transition point between G2 and M. Action on either one of these target periods could lead to a delay in the G2/M transition, but these two responses did not appear to be additive.