|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
Journal of Experimental Biology, Vol 201, Issue 3 425-438, Copyright © 1998 by Company of Biologists
JOURNAL ARTICLES |
L. Coelho, J. Prince and T. G. Nolen
The marine snail Aplysia californica obtains its purple defensive ink exclusively from the accessory photosynthetic pigment r-phycoerythrin, which is found in the red seaweeds of its diet. The rhodoplast digestive cell, one of three types of cell lining the tubules of the digestive gland, appears to be the site of catabolism of red algal chloroplasts (rhodoplasts) since thylakoid membranes, including phycobilisome-sized membrane-associated particles, were found within the large digestive vacuoles of this cell. Immunogold localization showed that there was a statistically significant occurrence of the red algal phycobilisome pigment r-phycoerythrin within these rhodoplast digestive vacuoles, but not in other compartments of this cell type (endoplasmic reticulum, mitochondria, nucleus) or in other tissues (abdominal ganglion). Immunogold analysis also suggested that the rhodoplast vacuole is the site for additional modification of r-phycoerythrin, which makes it non-antigenic: the chromophore is either cleaved from its biliprotein or the biliprotein is otherwise modified. The hemolymph had spectrographic absorption maxima typical of the protein-free chromophore (phycoerythrobilin) and/or r-phycoerythrin, but only when the animal had been feeding on red algae. Rhodoplast digestive cells and their vacuoles were not induced by the type of food in the diet: snails fed green seaweed and animals fed lettuce had characteristic rhodoplast cells but without the large membranous inclusions (rhodoplasts) or phycobilisome-like granules found in animals fed red seaweed. Two additional cell types lining the tubules of the digestive gland were characterized ultrastructurally: (1) a club-shaped digestive cell filled with electron-dense material, and (2) a triangular 'secretory' cell devoid of storage material and calcium carbonate. The following model is consistent with our observations: red algal rhodoplasts are freed from algal cells in the foregut and then engulfed by rhodoplast digestive cells in the tubules of the digestive diverticula, where they are digested in membrane-bound vacuoles; r-phycoerythrin is released from phycobilisomes on the rhodoplast thylakoids and chemically modified before leaving the digestive vacuole and accumulating in the hemolymph; the pigment then circulates throughout the body and is concentrated in specialized cells and vesicles of the ink gland, where it is stored until secreted in response to certain predators.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati 
Twitter What's this?
This article has been cited by other articles:
|
|
 |
|
  J. S. Prince and P. M. Johnson Ultrastructural comparison of Aplysia and Dolabrifera ink glands suggests cellular sites of anti-predator protein production and algal pigment processing J. Mollus. Stud., November 1, 2006; 72(4): 349 - 357. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. M. Johnson, C. E. Kicklighter, M. Schmidt, M. Kamio, H. Yang, D. Elkin, W. C. Michel, P. C. Tai, and C. D. Derby Packaging of chemicals in the defensive secretory glands of the sea hare Aplysia californica J. Exp. Biol., January 1, 2006; 209(1): 78 - 88. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Nolen and P. Johnson Defensive inking in Aplysia spp: multiple episodes of ink secretion and the adaptive use of a limited chemical resource J. Exp. Biol., January 4, 2001; 204(7): 1257 - 1268. [Abstract] [PDF]
|
|
