Nuclear Degeneration of Epidermal Cells of Senescing Soybean Cotyledons

Abstract

The pattern of senescence of soybean cotyledons of intact seedlings was characterized using interference microscopy, to measure nuclear dry mass, and nucleic acid staining and microdensito metry, to measure DNA and total nucleic acid content of the epidermal nuclei. Nuclear dry mass, DNA, and total nucleic acid content declined from 16 d after planting until the time of abscission. The effect of detaching cotyledons and floating them on water or the growth hormones, kinetin or IAA, during the senescence phase was examined. During the time when cotyledons of intact seed lings senesced and abscised, detached cotyledons showed no symptoms of senescence. Further, there was no change in the dry mass of nuclei in epidermal cells from cotyledons floated on water or kinetin but there was a significant increase in the dry mass of nuclei from cotyledons floated on IAA.