Variations in leaf soluble amino acids and ammonium content in subtropical seagrasses related to salinity stress.

A survey of leaf soluble amino acids was conducted for four subtropical seagrasses grown at several salinities. Proline functioned as an organic osmoticum in Halodule wrightii Aschers., Thallasia testudinum Banks ex Koenig, and Ruppia maritima L., while alanine functioned in an osmoregulatory capacity in Halophila engelmanni Aschers. When light-and salinity-induced variations in leaf NH(4) and amide-N levels were compared in Halodule, Thalassia, and Halophila, ability to regulate leaf NH(4) levels was correlated with osmoregulatory capacity and maintenance of selected amino acid contents.