Osmolyte accumulation in leaves of Tamarix ramosissima growing under various soil conditions in the Colorado River basin

Tamarixramosissima is a dominant species in desert riparian ecosystems in the western USA. It is a phreatophytic halophyte, with salt glands on the leaves. While osmoregulation is essential for turgor maintenance under high salinity, the dose–response relationship to salinity of various osmolytes in plants with salt glands is still unknown. We profiled crude leaf extracts of T. ramosissima to identify the metabolic compounds that contribute to its salt tolerance. We compared leaf cation, soluble sugar, amino acid, and betaine content among T. ramosissima samples from five points along the Colorado River. The leaf sodium content of T. ramosissima trees increased with increasing soil salinity. Under high salinity conditions, soluble sugar and betaine content did not increase, but amino acids did. The increase in proline accumulation was highly and positively correlated with leaf sodium content. Thus, proline appears to be the essential osmolyte that T. ramosissima accumulates in response to severe salt stress in desert riparian areas of the USA.