Osmotic adaption in Australian mangroves

Young and old leaves of twenty-three mangrove species from northern Queensland (Australia) were investigated for their mineral ion and organic solute content. With a few exceptions, the Na⁺ and the Cl-concentrations calculated on the basis of plant water (p.w.) were close to that of seawater and showed little age-induced changes. In some species, especially in Ceriops tagal, SO₄ ^2- accumulated with increasing leaf age. The most widely distributed organic solutes were pinitol and mannitol, which were stored up to 280 mM plant water. A negative correlation between pinitol and SO₄ ^2- was found in the case of Ceriops tagal. Other compatible solutes known for halophytes, such as proline and methylated quaternary ammonium compounds (MQAC), were present only in a few mangrove species. Proline occurred in two Xylocarpus species, while MQAC were accumulated by Avicennia eucalyptifolia, A. marina, Acanthus ilicifolius, Heritiera littoralis and Hibiscus tiliaceus. In all other species, low molecular weight carbohydrates (LMWC) were the main organic solutes.