X-Ray and Proton-Induced Ultrastructural Changes in Dividing Chlamydomonas reinhardi

Abstract

Early in the dark period of a 12-hr light, 12-hr dark synchronization regime cells of Chlamydomonas reinhardi are either in division or preparing for it, and are more sensitive to x and proton irradiation as expressed in terms of mortality and mechanisms of death exhibited by lethally injured cells. Irradiated and control cells were fixed for electron microscopic examination at intervals up to 5 days postexposure. X irradiation with 9000 R produced 69% mortality in 137c wild type cells and 71% mortality in the acetate-requiring strain ac-31. Ultrastructural responses observed in x-irradiated cells included nuclei with nonnuclear condensations and swollen nuclear envelopes, nuclear envelope rupture in cells in an advanced state of disorganization, multinucleate cells and changes in chloroplasts and mitochondria. Irradiation of dividing 137c cells with 1.5-MeV protons possessing a dE/dx of 200 MeV cm/sup 2//g produces 89% mortality following 9 krad and 98.3% following 18 krad. Proton-induced changes resembled those observed following x irradiation. Multiple nuclei per cell and variations in staining intensity of entire cells or parts of cells are documented. Two features absent in control cells were of special interest following both types of irradiation: (1) Cells were observed which remained joined in configurations closely resemblingmore » division profiles or division conformation. (2) Chromosomes and spindle fibers were present at a time not characteristic of the normal cell cycle.« less