Six nuclear mutants of corn, six of soybean, and seven of cotton displayed low temperature-induced virescence when grown in controlled environments. For the group of plants studied, an increase in leaf chlorophyll a/b ratio was correlated with a temperature-sensitive biosynthetic sequence leading to a reduction in total chlorophyll content. These pigment alterations were reflected in the composition and quantity of the two major chlorophyll-protein complexes of chloroplast membranes. Changes in the amount of the major light-harvesting chlorophyll-protein complex was a prime consequence of the nuclear mutations. A decrease in the light-harvesting chlorophyll component of the light reaction centers of the leaf may account for the decrease in size of the photo-synthetic unit frequently noted in chlorophyll-deficient mutants. Variations in the concentration of the chlorophyll-protein complexes in the chloroplast lamellae may be causally related to variations in CO(2) compensation points of mutant soybean and cotton plants.