Isopropyl N-phenylcarbamate affects spindle microtubule orientation in dividing endosperm cells of Haemanthus katherinae baker

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Abstract
The mitotic inhibitor isopropyl N-phenylcarbamate (IPC) effects changes in the ultra-structure of the dividing endosperm cells of Haemanthus katherinae. In cells treated with 10 p.p.m. IPC for 0.5-2 h the microtubules lose their parallel alignment and become oriented in radial arrays. These radial arrays are interpreted as micropoles of the spindle apparatus and are thought to be the focal points for the chromosomes as they aggregate into micronuclei. Thus, IPC has a markedly different effect on the structure of the spindle apparatus than colchicine, which is observed at concentrations of 50 p.p.m. for 1 h to destroy the microtubules in Haemanthus. The structure of the microtubules appears unaffected by IPC since those from control and treated cells are similar in diameter (22 nm), in degree of staining, and in sensitivity to the fixation. In addition, the chromosomes and cytoplasmic components such as mitochondria, plastids, dictyosomes, elements of the endoplasmic reticulum, and ribosomes are not structurally modified by treatment with IPC.