Effect of metal chelators of the pyridine series on chlorophyll pheophytinization

2,2’-dipyridyl and especially 1,10-phenanthroline are shown to be capable of removing magnesium from the porphyrin ring of the Chl a molecules in vitro and in vivo. It is hypothesized that photodynamic injury to plants exposed to light after 17 h treatment with 1,10-phenanthroline results from dark accumulation under its influence of both Chl precursors protoporphyrin and sum of Mg-protoporphyrin with its monomethyl ester which are active sensitizers of photodestructive processes and the product of Chl degradation, pheophytin, which apparently can also sensitize formation of singlet oxygen in vivo.