Iew. Obrien et al., MAJOR CHANGES IN CHROMATIN CONDENSATION SUGGEST THE PRESENCE OF AN APOPTOTIC PATHWAY IN PLANT-CELLS, Experimental cell research, 241(1), 1998, pp. 46-54
A large decrease in fluorescence intensity of propidium iodide (PI)-st
ained nuclei is observed during senescence of plant cells. The phenome
non reflects a decrease in accessibility of DNA to this fluorochrome a
nd is a consequence of chromatin condensation. This decrease is substa
ntially greater than usually found in animal nuclei whose chromatin un
dergoes condensation, e.g., during differentiation or quiescence. Chro
matin condensation was confirmed by analyses of (i) DNA accessibility
to DNase I, (ii) histone disassociation induced by HCl, (iii) saturati
on of binding sites by the PI fluorochrome (iv), and (v) visual inspec
tion by fluorescence and confocal microscopy, The extent of changes re
vealed by these assays was used to map progressive changes in chromati
n condensation which allowed us to identify different stages in an apo
ptosis-like pathway in plants. The initial step of chromatin condensat
ion which occurred prior to endonucleolytic DNA degradation was detect
ed by fluorescence and confocal microscopy and confirmed by a variety
of assays employing flow cytometry, The initial chromatin condensation
appears to be a reversible step in the early stage of apoptosis. The
loss of reversibility of chromatin condensation observed subsequently
may be a critical point in the cascade of apoptotic events, leading to
further irreversible changes during apoptosis in plants. (C) 1998 Aca
demic Press.