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Physiological and biochemical responses to salt stress in the mangrove

Abstract Physiological and biochemical responses induced by salt stress were studied in laboratory-grown young plants of the mangrove, Bruguiera gymnorrhiza. The growth rates and leaf areas were highest in the culture with 125 mM NaCl. Transpiration rates showed a diel periodicity when the plants were placed in water, but the oscillatory cycles disappeared for plants placed in higher | ELSEVIER Aquatic Botany 68 2000 15-28 Aquatic botany www.elsevier.com locate aquabot Physiological and biochemical responses to salt stress in the mangrove Bruguiera gymnorrhiza Taro Takemuraa Nobutaka Hanagataa Koichi Sugiharaa Shigeyuki Babab Isao Karubea Zvy Dubinsky a c a RCAST Research Center for Advanced Science and Technology The University of Tokyo 4-6-1 Komaba Meguro-ku Tokyo 153-8904 Japan b College of Agriculture University ofRyukyus Okinawa 903-01 Japan c Faculty of Life Sciences Bar-Ilan University Ramat-Gan 52900 Israel Received 27 July 1998 received in revised form 29 March 2000 accepted 20 April 2000 Abstract Physiological and biochemical responses induced by salt stress were studied in laboratory-grown young plants of the mangrove Bruguiera gymnorrhiza. The growth rates and leaf areas were highest in the culture with 125 mM NaCl. Transpiration rates showed a diel periodicity when the plants were placed in water but the oscillatory cycles disappeared for plants placed in higher salt concentration 250-500 mM NaCl . The transfer of plants from water to any higher salinity resulted in an immediate increase in transpiration. Both the steady-state rates of transpiration and light-saturated rates of photosynthesis decreased as the salt concentration was increased. The activities of the antioxidant enzymes superoxide dismutase SOD and catalase showed an immediate increase after the plants were transferred from water to high salinity reaching in 10 days five and eight times those of initial activities respectively. The activities of these two enzymes were not affected by salt concentrations up to 1000 mM NaCl twice that of seawater. 2000 Elsevier Science B.V. All rights reserved. Keywords Bruguiera gymnorrhiza Catalase Mangrove Photosynthesis Salt Superoxide dismutase Transpiration 1. Introduction Mangroves form unique communities in tropical coastal regions and tidal lowlands. They are considered an ecologically essential component in protecting adjacent .