Control of intracellular ion homeostasis is pivotal to plant salt tolerance. Plants have developed a number of mechanisms to keep ions at appropriate concentrations. Both transporters and channels on the plasma membrane play important roles in this function. Plant cyclic nucleotide-gated channels (CNGCs) in the plasma membrane are non-selective monovalent and divalent cation channels. So far, most studies on plant CNGCs have been conducted on heterologous systems. In planta, reverse genetic studies revealed the role of different CNGCs in cation uptake, transport and homeostasis. However, there is little information available about the functional characteristics of plant CNGCs. Among the 20 members of this protein family in Arabidopsis, only AtCNGC2 has been functionally identified as an ion channel; therefore, more functional characterization needs to be done on other members of this protein family. Several CNGCs were suggested to be involved in K+, Ca2+ and Na+ uptake and transport, but available information is scarce. This study investigated the relationship between CNGC10 and ion transport in Arabidopsis, with a particular emphasis on the involvement of CNGC10 in salt tolerance. Arabidopsis thaliana wild type (WT) and two AtCNGC10 antisense lines (A2 and A3) were used to characterise the impact of different level of salt stress on (i) root growth, ion concentration in tissues, ion fluxes across the root surface and intracellular ion concentration and pH at the seedling stage, and (ii) photosynthesis and ion concentration in tissues at the flowering stage. Plants of both antisense lines had higher K+ and lower Ca2+ and Mg2+ concentrations in shoots than WT plants when grown in non-salt control 1/4 Hoagland solution. Altered K+, Ca2+ and Mg2+ internal concentrations in AtCNGC10 antisense lines compared with WT plants under non-salt conditions indicated disturbed long distance ion transport, especially xylem loading/retrieval and/or phloem loading. The results of ion fluxes across the root surface also suggested that AtCNGC10 might be involved in transport of K+, Ca2+ and Mg2+ in tissue. Under sudden salt exposure, higher Na+ efflux and smaller K+ efflux in both antisense lines suggested that AtCNGC10 channels are involved in Na+ and K+ transport. The shoots of AtCNGC10 antisense lines A2 and A3 contained higher Na+ concentrations and significantly higher Na+/K+ ratios compared to WT, resulting in impaired photosynthesis and increased salt sensitivity in A2 and A3 than in WT plants. In contrast, seedlings of both antisense lines exposed to salt stress had lower shoot Na+/K+ ratios and longer roots than WT seedlings, indicating that A2 and A3 were more salt-tolerant than WT in the seedling stage, likely because growth is less dependent on photosynthesis in the seedling than in the flowering stage. These results suggested CNGC gene might play a different role during different developmental stages and in various plant organs.
| Identifer | oai:union.ndltd.org:ADTP/232991 |
| Date | January 2009 |
| Creators | Guo, Kunmei |
| Publisher | University of Western Australia. Faculty of Natural and Agricultural Sciences, University of Western Australia. School of Earth and Environment |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Kunmei Guo, http://www.itpo.uwa.edu.au/UWA-Computer-And-Software-Use-Regulations.html |
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