Heterogeneous Population of Mitochondria in Higher Plant Cells

Abstract

IT is generally accepted that aspartate is synthesized from oxaloacetate which is generated in the tricarboxylic acid cycle (TCA cycle) operating in the mitochondria. Work with plant tissue culture cells1, however, showed that, although 14C-labelled metabolites were oxidized in the TCA cycle, the 14C-oxaloacetate generated was not available for the synthesis of 14C-aspartate. This was attributed to the possible presence of more than one type of mitochondria. The concept of a heterogeneous population of mitochondria in plant cells was proposed in 1960 by Avers and King, who used histochemical techniques to study the mitochondria in the root tips of four species of grass2. Wilson and Bonner3 identified two enzymatically different populations of mitochondria isolated from peanuts collected at different stages of germination. Similar ideas have been advanced regarding the mitochondria in animal cells4. In the work reported here, double labelling techniques were used to elucidate further the presence and possible role of a heterogeneous population of mitochondria in plant cells.