No abstract

Gamma-irradiation dosages between 100 and 200 krad greatly stimulate the development of invertase activity in sugar-beet tissue. However, exposure of tissue to 800 krad virtually eliminates the production of invertase. The production of the enzyme in control and irradiated tissue requires RNA and protein synthesis. Failure of 5-fluorouracil to inhibit the development of invertase implies that the synthesis of ribosomal RNA is not required for enzyme production. A close correlation between irradiation-stimulated methylation of sRNA and enzyme production is noted. We suggest that the synthesis or modification of some RNA required for the translation of "masked invertase RNA" is stimulated by γ-irradiation.

No abstract

This study was initiated to determine the effects of gammairradiation on lettuce hypocotyl elongation and ribosomal RNA synthesis relative to gibberellic acid and 5-fiuorouracil treatment. Exposure of seeds to gamma-irradiation inhibited hypocotyl elongation of seedlings grown in continuous light and darkness. The presence of 5-fiuorouracil in the incubation medium significantly retarded hypocotyl elongation; however, gibberellic acid was stimulatory to elongation in seedlings grown from irradiated and unirradiated seeds. The synthesis of ribosomal RNA was selectively depressed by 5-fluorouracil while gibberellic acid stimulated incorporation of ^H-uridine into ribosomal and transfer RNA. The observed response implies that ionizing radiation is effective in decreasing the synthesis of ribosomal and transfer RNA which is correlated with lettuce hypocotyl elongation.