RECOVERY FROM ULTRA-VIOLET LIGHT-INDUCED DELAY IN CLEAVAGE OF ARBACIA EGGS BY IRRADIATION WITH VISIBLE LIGHT

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Abstract
Delay in time for cleavage of the zygote follows irradiation of either sperm or egg with u.-v. light. The u.-v. is much less effective on the egg. This observation together with the known high ribonucleic acid content of the cytoplasm suggests that the u.-v. inactivation is produced in the nucleus. There is growth of the u.-v.-induced effect in the sperm but not in the egg. Irradiation with visible light of either gamete does not alter the u.-v. effect but irradiation of the zygote markedly reduces the cleavage-delay time. The zygote is most reactive at 10 min. after fertilization which is approx. the time of onset of the pro-phase. The time for formation of the sperm aster and the time for completion of cleavage once initiated is not altered by u.-v. or visible light. The mitotic stage which is delayed by u.-v. and which responds most to visible light is the onset of prophase. Treatment with adenosine, streptomycin, folic acid and 2,4-diamino-5-p-chlorophenoxypyrimidine had no effect on either inactivation or photoreactivation. Toxic effects of photodecom-position products of riboflavin on sperm and on cleavage are described. Riboflavin itself had no effect on inactivation or photoreactivation.

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