A Comparison of X-Ray and Ultraviolet Effects on Chromosomes of Zea Mays.

REVIOUS workers have found that in maize the genetic analyses have indicated P an apparent difference between the action of X-ray and ultraviolet on (1) gene mutation, (2) the frequency of reciprocal translocations, (3) the type and frequency of endosperm deficiencies, (4) the ratio of endosperm deficiencies to embryo abortions, and ( 5 ) the types of embryo deficiencies. These contrasts have been fully discussed by STADLER and co-workers in a series of papers from 1936 to 1951 (STADLER and SPRAGUE 1937; STADLER 1939 and 1941; STADLER and ROMAN 1943 and 1948; STADLER and SWANSON 1951). This discussion will include only those points that have a direct bearing on the differences in the chromosomal aberrations induced by the two radiations. In Zea mays the frequency of reciprocal translocations is low following treatment with ultraviolet radiation in contrast to the frequency found following X-ray treatment (STADLER and SPRAGUE 1937; STADLER 1941). STADLER and SPRAGUE found reciprocal translocation figures a t diakinesis in 42 % of the 100 plants from X-rayed pollen and no translocations in the same number of plants from ultraviolet treated series. In these experiments the doses of X-rays and ultraviolet radiation used were about equally effective in producing endosperm deficiencies. Not only does it seem that the frequency of reciprocal translocations is dif€erent following treatment with ultraviolet radiation, but it has been suspected that the type of translocation is different (STADLER 1941). SINGLETON and CLARK (1940) recognized a type of translocation associated with a genic deficiency, called a deficiency translocation, in the progeny of ultraviolet treated pollen. A limited amount of evidence is available on the comparative frequency of deficiency translocations following X-rays and ultraviolet radiation. DEBOER (1945) found two deficiency translocations among 3513 plants following treatment with ultraviolet radiation but five deficiency translocations in 1670 plants from X-rayed pollen. When the occurrence of interstitial and terminal chromosomal deficiencies following X-rays and ultraviolet radiation is compared, a difference is found. Following the use of ultraviolet no cytologically proven cases of interstitial deficiencies have been reported. However, several interstitial deficiencies have been observed in plants from X-rayed pollen (MCCLINTOCK 1931 ; DEBOER 1945). A number of terminal deficiencies have been reported in progeny following treatment with ultraviolet radiation (STAD-