RESPIRATORY, PHOTOSYNTHETIC AND ULTRASTRUCTURAL-CHANGES ACCOMPANYING SALT ADAPTATION IN CULTURE OF EUCALYPTUS MICROCORYS

Salt tolerant shoot cultures of Eucalyptus microcorys (F. Muell.) were able to grow and tolerate 100 and 150 mmol.L-1 NaCl, where the normal salt sensitive shoots were unable to survive 50 mmol.L-1 NaCl. A comp arative study between the salt tolerant and salt sensitive shoots show ed that respiration was not significantly different between salt sensi tive shoots (without exposure to NaCl) and salt tolerant. shoots expos ed to 100 and 150 mmol.L-1 NaCl. Photosynthesis on the other hand was significantly increased in salt tolerant shoots when expressed on a ch lorophyll basis. However, when respiration or photosynthesis were expr essed on a leaf fresh weight basis, both significantly decreased in th e salt tolerant shoots compared to the salt sensitive shoots. Photosys tem I and ferredoxin NADP-oxidoreductase were relatively insensitive t o salt and actually increased in the salt tolerant shoots. Photosystem II and photosystem I+II were not changed significantly when measured on a chlorophyll basis, but did decrease when expressed on a leaf fres h weight basis. Chlorophyll fluorescence parameters such as photochemi cal efficiency (F-v/F-m) and quantum yield (Y) were increased in salt tolerant shoots exposed to 100 mmol.L-1 NaCl, but were significantly l owered by a salt concentration of 150 mmol.L-1 NaCl. Chloroplast ultra structural changes were apparent in salt tolerant shoots which include d the presence of large starch grains, dilation of the thylakoid membr anes, almost no grana were present, and enlarged mesophyll cells. The observations are interpreted in terms of maintenance respiration, phot ochemical activity, photoassimilation, altered chloroplast membrane st ructure and starch accumulation.