Reversal of α,α′-Dipyridyl-induced Porphyrin Synthesis in Etiolated and Greening Red Kidney Bean Leaves

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Abstract
The chemical induction of porphyrin synthesis has been investigated in etiolated and greening leaves of Phaseolus vulgaris L. var. Red Kidney. When these leaves are incubated in darkness with solutions of transition metal ion chelators such as α,α′-dipyridyl, 1,10-phenanthroline, pyridine-2-aldoxime, or other related aromatic heterocyclic nitrogenous bases, they synthesize large amounts of protochlorophyllide and Mg protoporphyrins. Greening leaves produce more porphyrin than do etiolated leaves under such conditions. If the leaves are then transferred to 1 millimolar solutions of various transition metal salts such as Fe2+, Zn2+, or Co2+ (but not Mn2+ or Mg2+), Mg protoporphyrin (monomethyl ester) synthesis immediately ceases and the pigment(s) rapidly disappear(s); protochlorophyllide synthesis gradually diminishes during 4 to 8 hours of treatment. The loss in Mg protoporphyrin(s) can be accounted for by a simultaneous increase in protochlorophyllide in partially greened leaves but not in etiolated leaves. In the latter, the decline in Mg protoporphyrin(s) initiated by the application of Zn2+ is retarded by low temperature and anaerobiosis but not by respiratory inhibitors. Cycloheximide inhibits the loss of Mg protoporphyrin(s) but does not affect their conversion to protochlorophyllide.