THE METHIONINE-RICH LOW-MOLECULAR-WEIGHT CHLOROPLAST HEAT-SHOCK-PROTEIN - EVOLUTIONARY CONSERVATION AND ACCUMULATION IN RELATION TO THERMOTOLERANCE

The evolutionary conservation of the low-molecular-weight chloroplast- localized heat-shock protein (LMW chlpHsp) in vascular plants was exam ined using immunological methods. An antibody (Ab(met)) specific to th e LMW chlpHsp was produced using a synthetic 28-residue peptide contai ning the most conserved elements of its unique ''methionine-rich domai n'' as an antigen. This antibody detected a heat-inducible low-molecul ar-weight chloroplast protein in plants of six divergent Anthophyta sp ecies, including C-3, C-4, CAM, monocot, and dicot species. Ab(met) al so detected a LMW chlpHsp in species from the Divisions Psilotophyta, Equisetophyta, Polypodiophyta, and Ginkgophyta. A preliminary examinat ion of the relationship between accumulation of the LMW chlpHsp and ha bitat was also conducted. Seven Anthophyta species originating from bo th warm-and cool-temperature habitats were grown at 28 degrees C and t hen heat stressed at 40 degrees C. A positive qualitative relationship between the accumulation of the LMW chlpHsp and organismal thermotole rance in these species was observed; similar results were obtained sep arately with four nonAnthophyta species. The strong evolutionary conse rvation of this LMW Hsp and its localization to the chloroplast, and t he correlation between production of this protein and plant thermotole rance, suggest that the LMW chlpHsp plays an important role in adaptat ion to heat stress.