Emerson Enhancement Effect in Chloroplast Reactions

Abstract

A study of the quantum yield of nicotinamide adenine dinucleotide phosphate (NADP) reduction, and O2 evolution in isolated spinach chloroplasts in separate and combined beams of monochromatic light, revealed the existence of (a) a decline in the quantum yield ("red drop") in the region where the long-wave form of chlorophyll a becomes the prime absorber of light energy, (b) an Emerson enhancement effect which is similar in magnitude, intensity dependence and wavelength dependence to that found in whole cell photosynthesis. The data suggest the existence of 2 photochemical reactions in the Hill reaction with NADP as the oxidant. The 2-pigment systems sensitizing the 2 photochemical systems can be tentatively identified as (1) the long-wave form of chlorophyll a, (2) chlorophyll b and the short-wave form of chlorophyll a (Chl a 670).