2Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow, Russia; fax: (495) 939-3181
* To whom correspondence should be addressed.
Received May 8, 2009; Revision received June 9, 2009
The effect of Ca2+ on programmed death of guard cells (GC) and epidermal cells (EC) determined from destruction of the cell nucleus was investigated in epidermis of pea leaves. Ca2+ at concentrations of 1-100 µM increased and at a concentration of 1 mM prevented the CN–-induced destruction of the nucleus in GC, disrupting the permeability barrier of GC plasma membrane for propidium iodide (PI). Ca2+ at concentrations of 0.1-1 mM enhanced drastically the number of EC nuclei stained by PI in epidermis treated with chitosan, an inducer of programmed cell death. The internucleosomal DNA fragmentation caused by CN– was suppressed by 2 mM Ca2+ on 6 h incubation, but fragmentation was stimulated on more prolonged treatment (16 h). Presumably, the disruption of the permeability barrier of plasma membrane for PI is not a sign of necrosis in plant cells. Quinacrine and diphenylene iodonium at 50 µM concentration prevented GC death induced by CN– or CN– + 0.1 mM Ca2+ but had no influence on respiration and photosynthetic O2 evolution in pea leaf slices. The generation of reactive oxygen species determined from 2′,7′-dichlorofluorescein fluorescence was promoted by Ca2+ in epidermal peels from pea leaves.
KEY WORDS: reactive oxygen species, calcium, programmed cell death, necrosis, guard cells, epidermal cells, leaves, pea