Ionic homeostasis and reactive oxygen species control in leaves and xylem sap of two poplars subjected to NaCl stress
Ruigang Wang (1, 2), Shaoliang Chen (1, 3, 4), Xiaoyang Zhou (1), Xin Shen (1), Lin Deng (1), Huijuan Zhu (1), Jie Shao (1), Yong Shi (1), Songxiang Dai (1), Eberhard Fritz (5), Aloys Hüttermann (5) and Andrea Polle (5)
1. College of Biological Sciences and Technology, Box 162, Key Laboratory of Tree and Ornamental Plant Genetics and Breeding
(Ministry of Education), Beijing Forestry University, Beijing 100083, P.R. China / 2. The Centre for Research Ecotoxicology and Environmental Remediation, Institute of Agricultural Environmental Protection, The
Ministry of Agriculture, Tianjin 300191, P.R. China / 3. Key Laboratory of Biological Resources Protection and Utilization in Hubei Province, Hubei Institute for Nationalities, Enshi
445000, P.R. China / 4. Corresponding author () / 5. Institut für Forstbotanik, Georg-August-Universität Göttingen, Büsgenweg 2, 37077 Göttingen, Germany / Received August 23, 2007; accepted December 4, 2007; published online April 1, 2008
Summary
We investigated the effects of increasing soil NaCl concentration on intracellular compartmentalization of salt and on the
activities of antioxidant enzymes (superoxide dismutase (SOD), ascorbic peroxidase (APX), catalase (CAT) and glutathione reductase
(GR)) and their role in the regulation of reactive oxygen species (ROS; O2–. and H2O2) in leaves and xylem sap of salt-tolerant Populus euphratica Oliv. and salt-sensitive P. popularis cv. 35-44. Mesophyll cells of P. euphratica exhibited a high capacity for NaCl exclusion and compartmentalization of salt in vacuoles compared with P. popularis. In P. popularis, the salt treatment resulted in large accumulations of Na+ and Cl– in leaves that induced significant increases in O2–. and H2O2 production despite marked increases in the activities of antioxidant enzymes in leaves and xylem sap. Separation of the isoforms
of leaf SOD, APX and CAT by polyacrylamide gel electrophoresis followed by in-gel activity staining revealed that the salt-induced
activities of APX and CAT were the result of increases in activities of all the isoenzymes. Leaf injury and shedding of aged
leaves occurred following the oxidative burst in P. popularis, indicating that the increased activities of antioxidant enzymes in P. popularis were insufficient to counter the harmful effects of ROS at high soil NaCl concentrations. Unlike P. popularis plants, P. euphratica plants did not exhibit an oxidative burst in response to the NaCl treatments, because of (1) a high salt exclusion capacity
and effective compartmentalization of salt in vacuoles, and (2) up-regulation of antioxidant enzymatic activities after the
onset of salt stress. We conclude that P. euphratica plants subjected to saline conditions control ROS homeostasis through two pathways: (1) by maintaining cellular ionic homeostasis
and thereby limiting the NaCl-induced enhancement of ROS production under long-term saline conditions; and (2) by rapidly
up-regulating antioxidant defenses to prevent oxidative damage.
Keywords:
APX, CAT, GR, H2O2, isoenzyme, leaf, Populus euphratica, Populus popularis, SOD, superoxide radical, X-ray microanalysis.
