LYSOSOMES IN THE RESPONSE TO SALINITY BY MYTILUS EDULIS L.

Abstract

This chapter describes the response to salinity by Mytilus edulis L. Mytilus edulis uses the cellular free amino acid pool during volume regulation in response to altered salinity. When salinity is increased, the additional free amino acids required may be derived from the degradation of cellular protein. The role of the lysosomal or vacuolar system in proteolysis is well established for mammalian cells. In marine bivalves, a lysosomal system is well developed. A lysosomal marker enzyme, that is, β- N -acetylhexosaminidase, increased in activity in the digestive cells of Mytilus exposed to an increase in salinity and the amount of free enzyme activity decreased relative to the total activity present, indicating an increase in enzyme latency. The concentrations of ninhydrin-positive-substances (NPS) are higher in lysosomes than in the cytosolic fraction in Mytilus and may account for more than 15% of the total cellular NPS pool. It is observed that following a rise in salinity, NPS concentration in the lysosomes increased and then declined, coincident with a decline in lysosomal integrity as measured by the latency of hexosaminidase. The total hydrolytic capacity of the lysosomal/vacuolar system increased over 12 h following a rise in salinity.