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JXB Advance Access published online on April 23, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm057
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© The Author [2007]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

Salt tolerance, salt accumulation, and ionic homeostasis in an epidermal bladder-cell-less mutant of the common ice plant Mesembryanthemum crystallinum

Sakae Agarie1, Toshifumi Shimoda1, Yumi Shimizu1, Kathleen Baumann5, Haruki Sunagawa1, Ayumu Kondo2, Osamu Ueno3, Teruhisa Nakahara4, Akihiro Nose1 and John C. Cushman5,*

1Faculty of Agriculture, Saga University, Saga, 840-8502, Japan
2Faculty of Agriculture, Meijo University, Tempaku-ku, Nagoya, 468-8502, Japan
3Plant Physiology Department, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan
4Research Laboratory, Bioresources Research Center, Kyushu Electric Power Company, Inc., Saga 849-0922, Japan
5Department of Biochemistry and Molecular Biology, MS200, University of Nevada, Reno, NV 89557-0014, USA

* To whom correspondence should be addressed. E-mail: jcushman{at}unr.edu

The aerial surfaces of the common or crystalline ice plant Mesembryanthemum crystallinum L., a halophytic, facultative crassulacean acid metabolism species, are covered with specialized trichome cells called epidermal bladder cells (EBCs). EBCs are thought to serve as a peripheral salinity and/or water storage organ to improve survival under high salinity or water deficit stress conditions. However, the exact contribution of EBCs to salt tolerance in the ice plant remains poorly understood. An M. crystallinum mutant lacking EBCs was isolated from plant collections mutagenized by fast neutron irradiation. Light and electron microscopy revealed that mutant plants lacked EBCs on all surfaces of leaves and stems. Dry weight gain of aerial parts of the mutant was almost half that of wild-type plants after 3 weeks of growth at 400 mM NaCl. The EBC mutant also showed reduced leaf succulence and leaf and stem water contents compared with wild-type plants. Aerial tissues of wild-type plants had approximately 1.5-fold higher Na+ and Cl– content than the mutant grown under 400 mM NaCl for 2 weeks. Na+ and Cl– partitioning into EBCs of wild-type plants resulted in lower concentrations of these ions in photosynthetically active leaf tissues than in leaves of the EBC-less mutant, particularly under conditions of high salt stress. Potassium, nitrate, and phosphate ion content decreased with incorporation of NaCl into tissues in both the wild type and the mutant, but the ratios of Na+/K+ and Cl–/ NOFormulacontent were maintained only in the leaf and stem tissues of wild-type plants. The EBC mutant showed significant impairment in plant productivity under salt stress as evaluated by seed pod and seed number and average seed weight. These results clearly show that EBCs contribute to succulence by serving as a water storage reservoir and to salt tolerance by maintaining ion sequestration and homeostasis within photosynthetically active tissues of M. crystallinum.

Key words: Epidermal bladder cells, halophyte, ice plant, ion homeostasis, Mesembryanthemum crystallinum, salt stress, succulence

Received 21 August 2006; Accepted 28 February 2007


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