Respiratory, Photosynthetic and Ultrastructural Changes Accompanying Salt Adaptation in Culture of Eucalyptus microcorys

Abstract

Summary 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 comparative study between the salt tolerant and salt sensitive shoots showed that respiration was not significantly different between salt sensitive shoots (without exposure to NaCl) and salt tolerant shoots exposed to 100 and 150 mmol · L−1 NaCl. Photosynthesis on the other hand was significandy increased in salt tolerant shoots when expressed on a chlorophyll basis. However, when respiration or photosynthesis were expressed on a leaf fresh weight basis, both significandy decreased in the salt tolerant shoots compared to the salt sensitive shoots. Photosystem I and ferredoxin NADP-oxidoreductase were relatively insensitive to 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 fresh weight basis. Chlorophyll fluorescence parameters such as photochemical efficiency (Fv/Fm) and quantum yield (Y) were increased in salt tolerant shoots exposed to 100 mmol · L−1 NaCl, but were significandy lowered by a salt concentration of 150 mmol·L−1 NaCl. Chloroplast ultrastructural changes were apparent in salt tolerant shoots which included the presence of large starch grains, dilation of the thylakoid membranes, almost no grana were present, and enlarged mesophyll cells. The observations are interpreted in terms of maintenance respiration, photochemical activity, photoassimilation, altered chloroplast membrane structure and starch accumulation.