Aging and Loss of Germination in Rye Seeds Is Accompanied by a Decreased Fragmentation of Nuclear DNA at Loop Domain Boundaries

To investigate the processes that occur in the embryo cell nuclei in the course of natural and accelerated aging of rye seeds, nuclear DNA structural organization into chromatin loop domains was studied. The loss of germination was shown to be accompanied by a decreased excision of chromatin loop domains. The study of chromatin accessibility to DNase I did not reveal any considerable changes in chromatin architecture that would explain the decreased DNA fragmentation at matrix attachment regions. A soluble nuclear protein of ca. 31 kD was found to manifest nuclease activity, which declined with the loss of germination. The study of DNA fragmentation in histone-depleted nuclei (nucleoids) disclosed a nuclease activity resistant to 2 M NaCl extraction and sensitive to the specific inhibitors of DNA topoisomerase II; the latter activity also declined with aging. The authors conclude that the changes in DNA fragmentation patterns in aging seeds were primarily caused by a decreased activity of the enzymes accounting for the excision of chromatin loop domains.