Measurements of redox activity at the plasmalemma

Salt (NaCl) tolerance of 3 eucalypt species ( Eucalyptus alba Reinw. ex Bl., E. camaldulensis Dehnh and E. microtheca f.v. Muell.) was studied: three-month-old seedlings grown in a greenhouse were watered by a saline solution (up to 700 m M ) for 1 month. Mineral, water and sugar contents were highly affected by the saline stress. Sodium, K and Ca were accumulated in the leaves. No significant differences were found between E. camaldulensis and E. microtheca , the tolerant species, in water and mineral contents. Sugar contents were greater in E. microtheca . In E. microtheca Na was highly accumulated in roots [up to 910 μmol (g fresh weight)⁻¹], less in stems [up to 580 μmol (g fresh weight)-1] and leaves [up to 410 μmol (g fresh weight)^−r]. Chloride was also accumulated, its content was greater than the total content of Na and K, especially in the salt-tolerant provenance. Potassium and Ca contents were variously affected by the saline stress whereas soluble protein, amino acid and sugar contents were increased. Just after the saline stress, plants showed a large increase in the Na content of the leaf while the decrease in the K content of the stem and leaf continued. Plants were killed by the stress, probably because of too high accumulation of Na in leaves or roots according to the provenance. Osmoregulation and especially the participation of Na are discussed.