Programmed cell death in plants under anaerobic conditions: Effect of Ag+

We investigated epidermal peels from the leaves of pea (Pisum sativum L.) consisting of a monolayer of the cells of two types: stomatal guard cells (GC) with chloroplasts and mitochondria and basic epidermal cells (EC) containing only mitochondria. As inducers of programmed cell death, we used KCN destroying the nuclei in GC and EC and chitosan that destroys nuclei only in EC. AgNO3 (10 μM) stimulated the destruction of nuclei in GC and EC induced by CN− and suppressed chitosan-induced destruction of nuclei in EC. The destruction of nuclei in GC induced by CN− occurred under aerobic conditions and was prevented under anaerobiosis. The destruction of nuclei in GC induced by (CN− + Ag+) occurred both under aerobic and anaerobic conditions and was not suppressed by antioxidants. Among the tested cations of metals (Ag+, Hg2+, Fe2+, Fe3+, Cu2+, and Mn2+), Ag+ turned out to be the most efficient in respect to the stimulation of cyanide-induced destruction of nuclei in GC. Half-maximum concentrations of Ag+ and Hg2+ were equal to 4–5 μM. In epidermal peels treated with chitosan, GC were permeable to propidium iodide; however, the nuclei in GC (in contrast to EC) were not destructed in the presence of chitosan. It was concluded that Ag+, acting as an electron acceptor during photosynthetic electron transfer in the chloroplasts from pea leaves, impeded the O2 evolution by the chloroplasts treated with ferricyanide or silicomolybdate as electron acceptors, impeded the consumption of O2 in the course of electron transfer from the (ascorbate + N,N,N′,N′-tetramethyl-p-phenylenediamine) to methylviologen and suppressed the production of reactive oxygen species (ROS) in GC and EC.