绿豆子叶衰老期间核酸代谢的变化

萌发绿豆的子叶自然衰老期间,核酸含量降低,RNA降低的幅度比DNA大。电泳分析结果表明,子叶衰老期间细胞核主带DNA明显降低;而迁移慢的卫星带DNA变化不大。在RNA各组分中,18S rRNA从衰老前期就开始降低;25S rRNA和4～5S小分子RNA到衰老后期才缓慢下降。DNase和RNase活性在子叶整个衰老期间都明显升高,是导致核酸含量下降的主要原因。~3H-核苷掺入试验表明,核酸的合成速率在子叶衰老前期有所上升,到衰老后期又降低。poly(A)~ -mRNA含量在子叶开始衰老时明显上升。

Changes in Metabolism of Nucleic Acids During Senescence of Mung Bean Cotyledons

Changes in contents and components of DNA and RNA during senescence of mung bean cotyledons were determined, and poly(A)-containing mRNA was separated from the total RNA by use of oligo(dT)-cellulose affinity chromatography. The results showed that the contents of both DNA and RNA decreased during the senescence of mung bean cotyledons (Fig. 1). Electrophoresis analysis indicated that the decline of nuclear DNA and 18 S rRNA was responsible for the decrease of DNA and RNA levels, respectively (Fig. 2, 3). During incipient senescence (2 to 3 days), the contents of poly(A)~ -mRNA increased markedly (Fig. 5). The synthetic rates of nucleic acids were tested by ~3H-nucleoside incorporation. It was shown that in the early stage of senescence (3 to 4 days), the synthesis of nucleic acids increased obviously, especially RNA (Fig. 7). This gave an implication that the early decline of total nucleic acid levels was not due to the failure of synthesis. The results from the determination of DNase and RNase activities showed that the enhanced hydrolysis of nucleic acids was the main cause of the decline of total nucleic acid levels. Based on these observation, it could be concluded that the metabolism of nucleic acids was very active during early senescence of mung bean cotyledons.