Free amino acids and osmoregulation in the intertidal pulmonate Onchidium tumidium |
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Authors: | S F Chew S Y Ho Y K Ip |
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Institution: | (1) Biology Division, School of Science, National Institute of Education, Nanyang Technological University, 469, Bukit Timah Road, Singapore 259756, Republic of Singapore, SG;(2) School of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 119260, Republic of Singapore, SG |
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Abstract: | The aim of this study is to elucidate the osmoregulatory capabilities of the intertidal pulmonate Onchidium tumidium. Our results indicate that O. tumidium could tolerate hyperosmotic stress more effectively than hypoosmotic stress. In 10% seawater (SW), it was capable of maintaining
its plasma hyperosmotic and hyperionic to the external medium. However, it rapidly gained weight in 10% SW, and no restoration
of body weight was observed. In contrast, in 90% SW it was able to recover its body weight partially. In a hyperosmotic medium,
accumulation of intracellular free amino acids (FAA) was responsible for cell volume regulation. The accumulated FAA might
originate from protein catabolism, which occurred in the internal organs (IO). In contrast, the relatively smaller amination:deamination
ratio of glutamate dehydrogenase in the body wall (BW) and IO of specimens exposed to hypoosmotic stress might lead to a higher
rate of amino acid catabolism. This was supported by the greater ammonia contents in the BW and IO of, and higher rate of
ammonia excretion by, specimens exposed to 10% SW.
Received: 11 March 1998 / Accepted: 2 May 1999 |
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