PHYSIOLOGICAL-CHANGES ACCOMPANYING THE INDUCTION OF SALT TOLERANCE INEUCALYPTUS MICROCORYS SHOOTS IN TISSUE-CULTURE

Shoot cultures of Eucalyptus microcorys (F. Muell.) were conditioned b y a stepwise increase in NaCl over 12 months to tolerate 100 and 150 m mol.L-1 NaCl, where normally they were unable to survive 50 mmol.L-1 N aCl. Growth was initially inhibited during salt adaptation, but it rec overed 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 p heophytin b. The adaptive period was accompanied by elevated levels of proline, glycinebetaine, sucrose and glucose, but not by higher amoun ts of choline and fructose. Levels of Na and Cl were elevated during t he adaptation process, and K was reduced. After salt adaptation, the s alt tolerant shoots in 100 mmol.L-1 NaCl had multiplication rates clos e to non-conditioned shoots (without NaCl), bur the number of leaves a nd leaf area was still inhibited by salt. Growth and pigments were red uced further in salt tolerant shoots exposed to 150 mmol.L-1 NaCl, acc ompanied by elevations only in the levels of proline, sucrose and gluc ose. Salt tolerant shoots in 150 mmol.L-1 NaCl appeared to have only h igher levels of Cl compared to the same shoots in 100 mmol.L-1 NaCl. T he observations are interpreted in terms of osmotic adjust ment during salt adaptation and possible toxicity by elevated levels of Na and Cl .