A CHEMICAL ANALYSIS OF EYE COLOR MUTANTS OF APIS MELLIFICA

The striking phenotype of fourteen eye-colour mutants of the honey bee (Apis mellifica) has been analysed chemically. The substances producing the eye colour of the mutants have been identified and characteristic changes of their pigment metabolism have been revealed. The ommochromes xanthommatin and several ommins cause the black eye colour of the wild type bee eye. Quite different from this are four white-eyed mutants that possess no ommochromes, but which can be distinguished by their pattern of colourless, in u.v.-light fluorescing substances. Owing to the deficiency of the enzyme tryptophanpyrrolase, the mutant s is unable to produce formylkynurenine, which normally follows tryptophan in pigment biosynthesis. This results in an excessive accumulation of tryptophan. Similar relations can be considered for i (accumulation of kynurenine) and cr [p] (accumulation of 3-hydroxykynurenine [3-HOK]), in which the formation of ommochrome is completely blocked at higher points of the biosynthesis chain. During the first days as adults, all white-eyed mutants lose most of their characteristic precursor substances by defaecation. After having injected kynurenine into s males and 3-HOK into i males, the eyes turn brown owing to a strong formation of ommochromes. In the mutants st, iu, and bk the biosynthesis of ommochromes is partly blocked only (leaky mutants). All mutants of the ch locus are characterized by a very high content of 3-HOK, which is not accumulated in the haemolymph (cr, p), but in the eye pigment cells, thus causing in ch1, ch2, and chb a green eye colour and an obvious green fluorescence. The intensity of the pigment block and the corresponding accumulation of 3-HOK vary greatly in ch mutants, causing different eye colours. The colour change of g eyes from red to black is based on the redoxbehaviour of the ommochromes. Pteridines have no influence on visible eye colour. Except for cr, all mutant, as well as wild type, eyes contain isoxanthopterin and 7-hydroxylumazin ( = violapterin). In addition, small amounts of biopterin, pterin, and pterin-6-carbonic acid (degradation product) were isolated from all mutant and wild type eyes. In cr, the pattern of pteridines is different from that of other mutants. The investigations show that for every mutant there is a specific pattern of pigments and their precursors. © 1969.