ACTION SPECTRA FOR BIOSYNTHESIS OF CHLOROPHYLLS a AND b AND β‐CAROTENE

Action spectra for the formation of chlorophyll b and β‐carotene were determined with etiolated wheat leaves and compared with the action spectrum for the formation of chlorophyll a determined for the same samples. The action spectra were measured with etiolated leaves which had been pre‐illuminated for 10 min and incubated in the dark for 4 h to eliminate induction of pigments. The action spectra for chlorophyll b and for β‐carotene accorded with the action spectrum for chlorophyll a and with the absorption spectrum of protochlorophyllide in intact etiolated leaves. It is postulated from this result with chlorophyll b that this pigment is formed from protochlorophyllide through chlorophyll a or some intermediates to chlorophyll a. Complexing between chlorophylls and β‐carotene and proteins is postulated to interpret the action spectrum for β‐carotene. It is assumed that the low concentration of chlorophylls formed photochemically limits the rate of complexing, and that consumption of β‐carotene for the complexing induces formation of new β‐carotene.