Nachweis der DNA-Synthese in Hypocotylen und Cotyledonen gehemmter und nicht gehemmter Keimlinge von Sinapis alba

Abstract

Etiolated elongating hypocotyls of Sinapis alba synthesize DNA 40-72 h after sowing. The increase in DNA content is about 62.5%. Four-hour pulse experiments showed an increasing rate of [(32)P]orthophosphate incorporation; the maximum rate was obtained 64-68 h after sowing. In the cotyledons DNA increase up to the 56th h after sowing; later the DNA-content remains constant. During this time the incorporation of (32)P into the DNA of the cotyledons decreases continuously.After simultaneous application of Fluordesoxyuridin (FdUrd) (4×10(-5)M) and thymidine (4×10(-4)M) or thymidylate (4×10(-4)M) 40-64 h after sowing, the growth rate was the same as that in H2O treated controls, whereas application of FdUrd (4×10(-5)M) alone inhibited growth.In the presence of FdUrd (4×10(-5)M) thymidine (4×10(-4)M) and thymidylate (4×10(-4)M) enhanced the specific activity of the DNA up to respectively 68% and 63% of that in the H2O treated controls. Hydroxyurea (4 mg/ml) inhibited DNA-synthesis and growth in the same manner as FdUrd.The prolonged DNA-synthesis and the reversal of the FdUrd effect by thymidine or thymidylate are discussed.

Control by Phytochrome of Cytoplasmic and Plastid rRNA Accumulation in Cotyledons of Mustard Seedlings in the Absence of Photosynthesis

“…pair of cotyledons) as a system of reference in a growing tissue can be principally interpreted in several ways. Although the DNA contents of mustard cotyledons, which grow largely by cell expansion (31), increases somewhat in darkness (1,31), no significant influence of continuous far red light on DNA contents could be detected (31). Selective amplification of rRNA genes which has been reported for certain lower organisms (e.g.…”