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

Abstract— 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.