Salt tolerance in the halophytic wild rice, Porteresia coarctata Tateoka

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Abstract
SUMMARY: While members of the genus Oryza are very sensitive to salinity, salt concentrations as high as 20% of that of seawater had no adverse effect on the growth of the tropical wild rice (Porteresia coarctata Tateoka) in experiments undertaken in a greenhouse in the UK. P. coarctata plants accumulated sodium and chloride ions in the leaves, but maintained a Na: K ratio as low as 0.7, even after 6 weeks of growth in 25% artificial seawater (ASW) where the Na: K ratio was 34. This ability to maintain a high K: Na ratio in the leaves is in part a consequence of the secretion of ions from the leaves. The ratio of Na: K in the secreted salt (more than 5 for plants growing in 25% ASW) is similar to that measured by X‐ray microanalysis in the vacuoies of hairs found in folds of the adaxial surface of the leaf lamina, suggesting that the secretions emanate from these hairs. The salt secreted by the hairs is an important factor in the salt‐balance of the leaves: the consequences of these findings for the transfer of salt‐tolerance from this species into cultivated rice are discussed.