N-BETA-ALANYLDOPAMINE METABOLISM FOR PUPARIAL TANNING IN WILD-TYPE AND MUTANT NIGER STRAINS OF THE MEDITERRANEAN FRUIT-FLY, CERATITIS-CAPITATA

N-beta-Alanyldopamine (NBAD) metabolism was investigated in wild-type and melanic mutant niger strains of the Mediterranean fruit by, Cerati tis capitata, during the process of pupariation, When radioactive beta -alanine (BALA) was injected at the onset of pupariation, the wild-typ e puparium incorporated 70% of the label, whereas less than 5% was det ected in the niger puparium. BALA was catabolized and eliminated as ca rbon dioxide substantially more in the mutant than the wild-type strai n, Significant differences between the two strains were found in the c omposition of catecholamines extracted from fully sclerotized puparial cuticle, NBAD levels in niger were five times lower than those in the wild type, whereas dopamine (DA) levels were 20 times higher. The con centration of NBAD in hemolymph also was greatly reduced in niger, whe reas DA and N-acetyldopamine levels remained high during pupariation, The synthesis of NBAD was assayed both in vivo and in vitro, revealing that the conversion of BALA into NBAD was several fold higher in the wild-type than in the niger strain, Because NBAD hydrolase activity wa s found to be similar in both strains, an impairment in NBAD synthesis appears to be responsible for the melanic phenotype. We also found th at NBAD synthesis in the wild type was restricted to a narrow developm ental window, which overlaps the time period in which puparial tanning occurs, Because we were able to induce niger-wild-type cuticle mosaic s in heterozygous embryos, NBAD synthetase appears to be expressed by the epidermis, We conclude that the niger mutant is defective in NBAD synthesis and that this defect prevents normal pigmentation.