Abstract
Defining seawater tolerance as a plant’s ability to survive under saline culture (seawater: average 500 mM NaCl), we attempted to identify gene sources as donors for this trait. Seawater-tolerance was observed in 42 plant species and spread over many families. In the family Gramineae, the presence of seawater tolerance was not random: a large cluster of seawater tolerance was found in the sub-family Eragrostoideae. In contrast, most grass crops, belonging to different sub-families, were susceptible in seawater culture. Evaluation of 369 native rice varieties and 105 wild rice collections showed that the critical lethality level of salinity in Oryza sativa L. was at around 50 mM (10% dilution of seawater). Two genes, PvUGE1 and PvMET1, were identified in one of the most tolerant Gramineae, seashore paspalum (Paspalum vaginatum). The PvUGE1 gene encodes putative UDP-galactose epimerase and the PvMET1 gene encodes metallothioneine. These had not yet been examined in the category of plants with salt tolerance. Although rice was very sensitive to salinity, both genes enhanced the salt tolerance of rice at the critical salinity level. PvUGE1 was significantly more effective than PvMET1, that is, PvUGE1 is one of the major genes associated with seawater tolerance, while PvMET1 is one of the supporter genes.
