Abstract
Quantitative studies on the tryptophan → ommochrome pathway are made in wildtype and mutant honey bees, Apis mellifera. The screening pigments xanthommatin and ommins are found in the bee eye at a quantitative proportion, depending on the particular developmental stage: the mature black wildtype-eye (drone, 12 days after emergence) contains xanthommatin far more than ommins, whereas the opposite relations are true for the violet coloured pupal eye. Characteristic pigment precursors (tryptophan and its derivatives) are accumulating temporarily in the haemolymph of all mutants except chartreuse. Herein the level of tryptophan proves to be very high (mutant snow); on the contrary, the amount of accumulated 3-hydroxykynurenine reaches rather low values only. The same compounds are accumulating in the clear rectal fluid at the reverse quantitative proportion. It can therefore be concluded that 3-hydroxykynurenine is removed from haemolymph faster than tryptophan. In consequence of an accumulation of kynurenine ( ivory) or 3-hydroxykynurenine ( cream, pearl, brick), the deaminated derivatives kynurenic acid resp. xanthurenic acid are found in pupae and young adults of the particular mutants. The new mutants ‘bayer’, ‘spade’, ‘eyeless’, are classified into the ommochrome pathway by their chemotype. Since the eyes of ‘ eyeless’ ♂♂ are extremely reduced in size, the tryptophan catabolism leading to ommochrome is almost totally missing. Hereby the amount of tryptophan is considerably increased in the haemolymph of young ‘ eyeless’ ♂♂. After having implanted tryptophan into the exstirpated eyes of ivory-mutants which had just emerged, kynurenine is being formed. This reaction was used, to estimate the activity of the enzyme tryptophan-oxygenase. Implanting of pigment precursor compounds in various mutants result in reactions, which demonstrate that the whole tryptophan → ommochrome pathway takes place in the eyes of bees.
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