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

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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 [32P]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 32P into the DNA of the cotyledons decreases continuously. After simultaneous application of Fluordesoxyuridin (FdUrd) (4×10-5M) and thymidine (4×10-4M) or thymidylate (4×10-4M) 40–64 h after sowing, the growth rate was the same as that in H2O treated controls, whereas application of FdUrd (4×10-5M) alone inhibited growth. In the presence of FdUrd (4×10-5M) thymidine (4×10-4M) and thymidylate (4×10-4M) 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.