Developmental regulation of the plant mitochondrial matrix located HSP70 chaperone and its role in protein import

Changes in the level of the mitochondrial chaperone mtHSP70 have been investigated in pea (Pisum sativum) leaf mitochondria by Western blot analysis and quantified by scanning densitometry. As pea leaves develop (from 6 days to 30 days of age) the levels of mtHSP70 decrease. Analysis of the levels of the α subunit of the F1ATPase show that the levels of this protein remain constant throughout the same developmental period, whereas the levels of the alternative oxidase increase. In vitro import of the alternative oxidase precursor protein into pea leaf mitochondria from day 6 to day 30 leaves and quantification by scanning densitometry indicates that protein import efficiency decreases with increasing maturity of the plant cell. Results are discussed in terms of how changing levels of the mtHSP70 chaperone, as a result of plant cell development, influence the efficiency of protein import.