Fig. 4.

Mutants in the LRO-biogenesis pathway fail to accumulate riboflavin in the Malpighian tubules. The Malpighian tubules of adult females are shown for the indicated genotypes along with the concentration of total body zinc in mg Zn g⁻¹ dry mass. (A) Riboflavin in wild-type Malpighian tubules gives them their characteristic yellow-orange color (Nickla, 1972). (B–D) Three representative LRO-biogenesis mutants are all colorless and low in zinc. A comparison between isogenic (E) w⁺ and (F) w* suggests that the w gene is required for the accumulation of both riboflavin and zinc. (G) The bw mutants are severely reduced in their coloration and less so in their zinc content. (H) The st mutants show riboflavin coloration, but severely reduced zinc concentration.