Effect of plastid development on the 518 nm absorbance change in bean leaves

The light-induced absorbance change at 518 nm was studied in etiolated bean leaves greened in periodic light. It was found that contrary to green leaves: (a) The periodic-light leaves show a light-induced decrease in absorbance both at 518 and 480 nm (reference wavelength 540 nm). (b) The time course of the change at 518 and 480 nm is identical, and the signal as well as the dark decay is biphasic. A second illumination induces also a biphasic signal. (c) Transfer of the periodic-light leaves to continuous illumination induces a gradual decrease in the magnitude of the 518 nm change (measured as ΔA518480), which reaches zero, then increases, becoming positive and finally reaches the value of the green leaves. No change is observed in the 470–510 nm region of the spectrum. At the same time the kinetic characteristics at 518 and 480 nm change from that of periodic-light leaves to that of green leaves. In the intermediate stage there are samples that behave like green leaves in the 510–540 nm region and like periodic-light leaves in the 470–510 nm region. The results suggest that the “518 nm effect” is probably the net result of more than one phenomena.