A unique visual pigment expressed in green, red and deep-red receptors in the eye of the small white butterfly, Pieris rapae crucivora

Abstract

The full primary structure of a long-wavelength absorbing visual pigment of the small white butterfly, Pieris rapae crucivora, was determined by molecular cloning. In situ hybridization of the opsin mRNA of the novel visual pigment (PrL) demonstrated that it is expressed in the two distal photoreceptor cells (R3 and R4) as well as in the proximal photoreceptors (R5-8) in all three types of ommatidia of the Pieris eye. The main, long-wavelength band of the spectral sensitivities of the R3 and R4 photoreceptors is well described by the absorption spectrum of a visual pigment with absorption maximum at 563 nm; i.e. PrL is a visual pigment R563. The spectral sensitivities of R5-8 photoreceptors in ommatidial type I and III peak at 620 nm and those in type II ommatidia peak at 640 nm. The large shifts of the spectral sensitivities of the R5-8 photoreceptors with respect to the absorption spectrum of their visual pigment can be explained with the spectral filtering by pale-red (PR) and deep-red (DR) screening pigments that are concentrated in clusters of granules near the rhabdom boundary. The peak absorbance of the two spectral filters appears to be approximately 1 (PR) and 2 (DR).