Physiological changes accompanying the induction of salt tolerance in Eucalyptus microcorys shoots in tissue culture

Shoot cultures of Eucalyptus microcorys (F. Muell.) were conditioned by a stepwise increase in NaCl over 12 months to tolerate 100 and 150 mmol.L-1 NaCl, where normally they were unable to survive 50 mmol.L-1 NaCl. Growth was initially inhibited during salt adaptation, but it recovered over time, even though NaCl concentrations were being increased. During salt adaptation, photosynthetic pigments (chlorophyll a and b, protochlorophyll, pheophytin a, carotenoids) were reduced, but not pheophytin b. The adaptive period was accompanied by elevated levels of proline, glycinebetaine, sucrose and glucose, but not by higher amounts of choline and fructose. Levels of Na and Cl were elevated during the adaptation process, and K was reduced. After salt adaptation, the salt tolerant shoots in 100 mmol.L-1 NaCl had multiplication rates close to non-conditioned shoots (without NaCl), bur the number of leaves and leaf area was still inhibited by salt. Growth and pigments were reduced further in salt tolerant shoots exposed to 150 mmol.L-1 NaCl, accompanied by elevations only in the levels of proline, sucrose and glucose. Salt tolerant shoots in 150 mmol.L-1 NaCl appeared to have only higher levels of Cl compared to the same shoots in 100 mmol.L-1 NaCl. The observations are interpreted in terms of osmotic adjust ment during salt adaptation and possible toxicity by elevated levels of Na and Cl.