CONSEQUENCES OF UNILATERAL ULTRAVIOLET RADIATION OF SEA URCHIN EGGS

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Abstract
The dose-dependent in-hibition of the fertilization reaction in the directly-irradiated hemisphere of the unilaterally UV-irradiated sea urchin egg is described. Changes in the ability to elevate the fertilization membrane and to differentiate the hyaline layer were sought. Membrane elevation was not activated. The injury was not temperature sensitive and did not spread with time, indicating a direct photochemical action. The irradiated hemisphere maintained its jelly. Partial gelation of the directly-irradiated hemisphere was seen. The gelled cytoplasm had a higher density than the rest of the egg. Irradiation in calcium-free sea water did not alter UV damage observed after fertilization in sea water. The behavior of the cytoplasm of the shaded hemisphere at fertilization suggested either that the surface structure was damaged or that the osmotically inert volume had been increased. Unilateral irradiation caused eccentric spindle formation which resulted in equal sized blastomeres if the spindle axis was perpendicular to the axis of irradiation and unequal sized blastomeres if the axes were parallel.

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