IP Nutrition

Homeostasis and physiology on Vitamin B2 of the silkworm, Bombyx mori

Dept. of Sericulture, National Inst. of Sericultural and Entomological Sci., 1-2 Ohwashi Tsukuba Ibaraki 305-8634 Japan

The effects of lack of vitamin B2 on the growth and physiology of the silkworm was examined. When silkworm larvae were reared on a vitamin B2 deficient diet, their growth retarded gradually whereas the total vitamin B2 content in larval body was decreased rapidly. This decrease was mostly due to the fall of riboflavin content; FAD and FMN, the coenzyme forms of vitamin B2, changed in content only slightly. There were no changes in activity of xanthine dehydrogenate that requires FAD for coenzyme. A large amount of riboflavin was accumulated in the Malpighian tubules but this almost disappeared when the larvae were reared on a vitamin B2 deficient diet. When the supply of vitamin B2 to the larvae is deficient, riboflavin accumulated in the Malpighian tubules may act as a pool for the homeostasis of FAD and FMN. The activity of flavokinase that catalyzes the formation of FMN from riboflavin was found to be high in the Malpighian tubules. This enzyme, therefore, would play a part in the incorporation of riboflavin into the Malpighian tubules. As the activity of flavokinase was also high in the midgut, it may function during the ingestion of vitamin B2 from diet. When larvae were reared on a vitamin B2 deficient diet from the beginning of the 3rd instar, the activities of flavokinase in the midgut and Malpighian tubules at the 5th instar were higher than the control. The increased activity possible favors the increased supplement of the coenzymes forms of vitamin B2. Since there was no changes in flavokinase activity when larvae were reared on a vitamin B2 deficient diet from the beginning of the 5th instar, so that the coenzyme forms will be supplied from a riboflavin pool by the increased flavokinase activity only in the serious shortage of vitamin B2.

Index terms: Bombyx mori, riboflavin, flavokinase, Malpighian tubules

Copyright: The copyrights of this abstract belong to the author (see right-most box of title table). This document also appears in Session 13 – INSECT PHISIOLOGY, NEUROSCIENCES, IMMUNITY AND CELL BIOLOGY Symposium and Poster Session, ABSTRACT BOOK II – XXI-International Congress of Entomology, Brazil, August 20-26, 2000.