SYNTHESIS OF PIGMENT DURING THE RECONSTITUTION OF TUBULARIA

¹ Arnold Biological Laboratory, Brown University, Providence, R. I.

1. The origin of the red pigment in the hydranth-forming region of reconstituting stem segments of Tubularia has been investigated histologically and spectrophotometrically.

2. Short (1.5 to 2 mm.), perisarc-enclosed segments, isolated from extrinsic sources of pigment (e.g., ingested materials or other non-regenerating regions of the stem), reconstitute with normal reddening.

3. Histological observations have failed to demonstrate the presence of red algae within the coenosarc of Tubularia. Therefore, red algae do not play a critical role in the increased coloration.

4. A spectrophotometric assay of the pigment concentration in short segments at successive intervals in the reconstitutive process has provided evidence that the total amount of pigment increases during regeneration. It is concluded that the coenosarc of regenerating segments synthesizes new pigment. This finding is of interest because the pigment is presumably a carotenoid and because no conclusive evidence has previously been presented that animals synthesize carotenoids.

5. Microscopically, pigment is found in two forms: 1) large, irregular and birefringent granules sparsely distributed in the gastrovascular fluid and in certain endodermal cells, and 2) minute anisotropic crystals occurring in large numbers in the endoderm. The reddening of the hydranth anlagen is presumably due to an increase in the number of pigment crystals.

6. During reconstitution, sudanophilic substances increase markedly in the presumptive hydranth endoderm. As the distal coenosarc endoderm transforms into hydranth endoderm, it develops the characteristic adult level of sudanophilia.

7. The possible morphogenetic roles of pigment and sudanophilic materials during reconstitution are discussed. While there is no certain relation of these substances to the morphogenetic process, further analyses are suggested.

8. The breakdown of the endodermal ridges in normally reconstituting segments, and the lack of endodermal ridge breakdown in non-reconstituting segments, indicate a possible role of these structures in the regenerative process.

9. A straw-yellow pigment, chemically different from the characteristic red pigment, is obtained when reconstituting segments are treated with heat or copper sulfate. This yellow pigment may be similar to that occurring occasionally in natural populations of Tubularia.