Compatible solutes and inorganic ions in the mangrove plant Avicennia marina and their effects on the activities of enzymes

Abstract

Naturally grown two-month-old seedlings of Avicennia marina contain high concentrations of Na+ and Cl-. Our NMR studies revealed an accumulation of glycinebetaine, asparagine and stachyose in A. marina. The highest concentration of glycinebetaine was observed in young leaves, while the distribution of stachyose was restricted in stems and roots. Asparagine comprised more than 96% of total free amino acids in roots and 84% in leaves from two-year-old plants. Little or no accumulation of proline or polyols, which are proposed as compatible solutes in other plants, could be detected in A. marina. The activities of phosphofructokinase, pyrophosphate:fructose-6-phosphate 1-phosphotransferase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase (decarboxylating), phosphoenolpyruvate carboxylase and NAD:malate dehydrogenase from young leaves of A. marina were inhibited by NaCl, while the activity of fructose-1,6-bisphosphate aldolase was activated by 50-200 mM NaCl. There was little or no effect of high concentrations (up to 500 mM) of glycinebetaine on the activities of any of these enzymes. No significant protection by glycinebetaine was detected against NaCl inhibition of these enzymatic activities. Based on these results, possible mechanisms for the salt-resistance of A. marina cells are discussed.