Effects of NaCl-salinity on amino acid and carbohydrate contents of Phragmites australis

The effects of NaCl-salinity on growth, free amino acid and sugar content and composition were assayed in roots, rhizomes and leaves of Phragmites australis (Cav.) Trin. ex Steud. Juvenile plants produced from freshwater clones, were cultured under greenhouse hydroponic conditions for 21 days. Relative growth rates were highest at a salinity level of 0 and 1.5 parts per thousand, respectively, but decreased significantly at 10 parts per thousand. All plants cultured at 35 parts per thousand salinity died. The osmolality in rhizomes and leaves increased with salinity. The total contents of free amino acids were highest in rhizomes > leaves > roots. In rhizomes, the amino acid content increased significantly up to four-fold from 0 to 10 parts per thousand salinity. This increase was caused by up to 200-fold increase of proline and 11-fold increase of glutamine at 10 parts per thousand, whilst the share of asparagine and glutamate decreased. Leaves showed a similar response to salinity with increasing amino acid contents, and shares of proline and glutamine whereas roots did not react significantly. The contents of sucrose, glucose and fructose were highest in leaves > rhizomes > roots. In rhizomes of all three clones, the sugar contents increased up to 3.5-fold from 1.5 to 10 parts per thousand salinity level, but were lower at 1.5 parts per thousand versus the control (0 parts per thousand). Sugar contents were lowest (roots) and highest (leaves) at 1.5 parts per thousand salinity. The sugar composition did not vary significantly except for leaves where the fraction of sucrose decreased with increasing salinity level at all three clones from 89.1 to 61.7% of total dissolved sugar (pooled data). The importance of free amino acids and sugars as osmolytes was similar in rhizomes and leaves (13-15% of total osmolality at 10 parts per thousand). In rhizomes, free amino acids were more important as osmolyte than sugars, while the opposite was true for leaves. Proline contributed up to 2.7% to total osmolality. It is hypothesised that a strong proline accumulation indicates the exceeding of a critical salinity level. (C) 2001 Elsevier Science B.V. All rights reserved.