THE 23-KDA LIGHT-STRESS-REGULATED HEAT-SHOCK-PROTEIN OF CHENOPODIUM-RUBRUM L IS LOCATED IN THE MITOCHONDRIA

The 23-kDa nuclear-encoded heat-shock protein (HSP) of Chenopodium rub rum L. is regulated by light at the posttranslational level. Higher li ght intensities are more effective in inducing the accumulation. of th e mature protein under heat-shock conditions. Based on this and other properties the protein was considered to belong to the group of small chloroplastic HSPs. However, we have now obtained the following eviden ce that this 23-kDa HSP is localized in the mitochondria: (if Immunogo ld-labelled protein was almost exclusively restricted to the mitochond ria in electron microscope thin sections. (ii) Using purified, isolate d mitochondria from potato tubers the in-vitro-synthesized translation product of 31 kDa was readily transported into mitochondria where it was processed to the 23-kDa product. (iii) The protein could be detect ed by Western blotting in a preparation of washed mitochondria of Chen opodium, while under the same conditions no signal could be obtained i n a preparation of isolated chloroplasts. (iv) Finally, sequence compa rison with the published sequences of mitochondrial proteins by Lenne et al. (1995, Biochem J 311:805-813) and LaFayette et al. (1996, Plant Mol Biol 30:159-169) showed clearly that the 23-kDa protein is consid erably more similar to these two proteins than to the group of plastid small HSPs. From these data we infer that mitochondria are involved i n the response of the plants to high light stress under heal-shock con ditions.