DNA changes involving repeated sequences in senescing soybean (Glycine max) cotyledon nuclei

Abstract

Age‐related DNA changes in soybean (Glycine max L. cv. Ransom) cotyledon nuclei were investigated by Feulgen cytophotometry and cloned DNA probes. The amount of nuclear DNA in 17‐day‐old senescing cotyledons was 23% lower than that of 5‐day‐old young cotyledons. In order to understand the nature of senescence‐related DNA loss, fragments of repetitive DNA from young cotyledons were cloned into Escherichia coli HB101 cells by DNA recombination. The cloned DNA probed changes in specific repeated nucleotide sequences in senescing cotyledons. The colony hybridization between cloned DNA and [32P]‐labeled total DNA from 5‐ and 17‐day cotyledons indicated loss of specific repeated sequences. The selected sequences of repeated DNA further showed a loss in their copy numbers. The study suggested that some repetitive DNA sequences were degraded selectively in the genome of senescing cotyledons.

Nuclear size and DNA content of the embryo and endosperm during their initial stages of development in Glycine max (Fabaceae)

“…Senescence of these cells likely included the loss of nuclear DNA and, therefore, an increased incidence of nuclei with reduced ploidy levels. A similar correlation between cellular degradation and DNA loss has been noted in the endosperm of maize (Kowles, Srienc, and Phillips, 1990) and wheat (Chojecki, Bayliss, and Gale, 1986) and in the senescent cotyledons of soybean (Chang, Miksche, and Dhillon, 1985).…”

DNA fragmentation is regulated by ethylene during carpel senescence in Pisum sativum

“…endocarp cells) but whose senescence was prevented by the ethylene action inhibitors (compare triple layer of endocarp cells in Figure 3(a) with endocarp cells in an already collapsed stage in Figure 3e). It is interesting to note that only a few reports in plant literature give DNA damage or alteration at the nuclear levels an important role in plant senescence (Chang et aL 1985;Cheah and Osborne, 1978;Modak and Bollum, 1972;Osborne, 1980). This is possibly because in most cases senescence has been studied in leaves where the chloroplast is the first organelle showing the effects of senescence, and the effects on the nuclei occur rather late.…”

DNA and RNA Levels in Bundle Sheath and Mesophyll Cells of Pearl Millett (Pennisetum americanum)

“…One likely explanation for the difference in DNA content is the selective amplification or loss of nuclear material in one cell type versus the other. Because of the size range of 2C values reported for various millet tissues, we cannot distinguish between amplification or loss of nuclear sequences, and evidence for both has been reported (7,8). Amplification of selected DNA sequences is generally associated with increased transcription of the amplified region, which might lead to an increase in RNA.…”

“…1C) and mesophyll cell nuclei, and the distributions of relative DNA contents of the two cell types are shown in Figure 2 Although several possibilities can be offered to explain the higher DNA content of mesophyll cells, we are not yet able to determine which accounts for the differences reported here. Among the possibilities are polyploidization, differential cell cycle arrest, selective chromosome duplication or DNA amplification, and/ or selective loss of DNA or chromosomes (8,12,13,15). In many plant species, DNA endoreduplication is an important feature of cell development (1), although it is not considered essential for tissue or organ differentiation in all higher plants (15).…”