Overexpression of DnaK from a halotolerant cyanobacterium Aphanothece halophytica acquires resistance to salt stress in transgenic tobacco plants

To test the role of the heat shock protein DnaK/Hsp70 in salt tolerance, tr ansgenic plants of Nicotina tabacum cv Petit Havana SR1 were made with DnaK 1 from a halotolerant cyanobacterium Aphanothece halophytica (A. halophytic a) overexpressed in the cytosol. The growth rate and photosynthetic activit ies of the transgenic and control tobacco plants were similar under non-str essed conditions. The CO2 assimilation rate of the control plants decreased with increasing concentration of NaCl. After 3 days of treatment with 0.6 M NaCl, the CO2 fixation rate decreased to 40% of that in the non-stressed plants whereas its activity in the transgenic plants was about 85% of that in the non-stressed plants. Similar results were observed for the stomatal transpiration. The sodium contents in leaves of the control plants were sig nificantly increased by salt stress whereas those in the transgenic plants remained at levels similar to those in the non-stressed plants. Total prote in contents and ribulose 1,5-bis phosphate carboxygenase and oxygenase (RuB isCO) levels were decreased by salt stress in both the transgenic and contr ol plants but the decrease was slight in the transgenic tobacco. All these data clearly indicate that the expression of DnaK1 from a halotolerant cyan obacterium A. halophytica improved the salt tolerance of the tobacco plant. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.