[Quantitative studies on the pigmentation of the eye in the flourmothEphestia kühniella : II. Pigmentation in the,a-strain after injection of small amounts 3-hydroxykynurenine].

The rate of ommochrome synthesis in the accessory pigment cells has been studied after injecting various amounts of the ommochrome precursor 3-hydroxykynurenine (3-HOK) into pupae of the red-eyed strain. The rate of pigment synthesis is proportional to the injected dose, provided it does not exceed 1μm per pupa. - Injection at 96-99 hours after pupation causes a short but fast rise of the rate, which is followed by an exponential decrease to about one half of its initial value within a 12 hour's period. - The amount of pigment being synthesized until 180-183 hours after pupation decreases with increasing time of injection. Quantitative comparison of this decrease with pigment synthesis after injection at 96-99 hours allows the conclusion that the exponential drop of the rate after supplying the precursor at 96-99 hours is not due to the decrease of precursor concentration within the pupa. It must be brought about exclusively by developmental processes of the pigmentary system itself. - If an injection of 1 μg 3-HOK atti >99 hours succeeds a first one given at 96-99 hours, the amount of pigment being synthesized betweenti and 181.5 hours is 1.73 times the amount being synthesized after a single injection atti. This value is independent ofti. - The discussion of these results calls for a special mechanism which will adjust the activity of the pigmentary system to the total amount of the precursor.