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Plant and Cell Physiology Advance Access published online on February 28, 2008
Plant and Cell Physiology, doi:10.1093/pcp/pcn037
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© The Author 2008. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Heat Stress Stimulates Nitric Oxide Production in Symbiodinium microadriaticum: A Possible Linkage between Nitric Oxide and the Coral Bleaching Phenomenon.

BOUCHARD Josée Nina* and YAMASAKI Hideo

University of the Ryukyus, Nishihara, Okinawa, 903-0213, Japan

Corresponding author: Dr. Josee Nina Bouchard. University of the Ryukyus, Nishihara, Okinawa, 903-0213, Japan, E-mail: josee_bouchard{at}yahoo.com


  Abstract

Nitric oxide (NO) is a gas displaying multiple physiological functions in plants, animals, and bacteria. The enzymes nitrate reductase and NO synthase have been suggested to be involved in the production of NO in plants and algae but the implication of those enzymes in NO production under physiological conditions remains obscure. Symbiodinium microadriaticum, commonly referred as to zooxanthellae, is a marine microalga commonly found in symbiotic association with a cnidarian host including reef-building corals. Here we demonstrate NO production in zooxanthellae upon supplementation of either sodium nitrite or L-arginine as a substrate. The nitrite-dependent NO production was detected electrochemically and confirmed by the application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger. Cells stained with DAF-2 DA, a NO fluorescent probe, showed an increase in fluorescence intensity upon supplementation of both sodium nitrite and L-arginine. Microscopic observations of DAF-stained cells verified that NO was produced inside the cells. NO production in S. microadriaticum was found to increase upon cells exposure to an acute heat stress which also caused a decline in the photosynthetic efficiency of the photosystem II (Fv/Fm). This study provides substantial evidence to confirm that zooxanthellae can synthesize NO even when they are not in a symbiotic association with a coral host. The increase in NO production at high temperatures suggests that heat stress stimulates the microalgal NO production in a temperature-dependent manner. The implications of these findings are discussed in the light of the coral bleaching phenomenon which is associated with elevated seawater temperature due to global warming.

Keywords: Coral bleaching - Symbiodinium microadriaticum - Nitrate reductase - Nitric oxide - Nitric oxide synthase - Temperature

(Received December 17, 2007; Accepted February 26, 2008)
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