All plant cells must actively export sodium from the cytoplasm. Accumulation of sodium in the cytoplasm results in inhibition of a number of enzyme systems, and is a major cause of damage due to salinity, whether natural or due to irrigation of agricultural fields. A knowledge of the mechanisms of Na+ transport is therefore not only important in general understanding of the function of plants, but also enhances our ability to develop crop plants which are more resistant to salinization. This project will use two species of Charophyte algae that differ in their ability to tolerate saline conditions. Re-moval of Na+ from the cytoplasm by export across the plasma mem-brane is important in achieving salt tolerance, and there is evidence that an ATPase may be involved in this transport, including biophysical evidence that a Na+/H+ antiport is not sufficient to maintain the Na+ gradients measured, immunological evidence of an unusual P-type ATPase in salt-cultured algae, and molecular evidence for an unusual P-type ATPase in the salt-tolerant algae.
The objectives of the proposed research are To isolate and sequence a full-length clone for an unusual ATPase from the salt-tolerant species, Chara longifolia. To use northern blot analysis to determine expression of this gene in C. longifolia adapted to saline and freshwater media, and undergoing adaptation to salt stress. To determine whether the salt-sensitive species, C. corallina, has a similar gene and, if so, under what conditions it is expressed.
Long-term goals include determining the transport function of the ATPase gene either by expres-sion in yeast mutants lacking Na+ or H+ export capability or by overexpression in Chara by micro-injection of mRNA into the internode. Ultimately, information based on this research could be used to alter the salt tolerance of Chara and other plants by genetic manipulation to enhance sodium export from the cytoplasm.
This research will be performed under the POWRE grant program because it will aid the author in remaining competitive in the field of salinity studies in plants. Bio-physical techniques have been successfully employed in the past to investigate important ques-tions in this field, but molecular aspects of the project must be developed in order to remain competitive.
