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Articles

Studies on Ultrastructure and Purification of Isolated Plant Mitochondria ¹

United States Department of Agriculture, MQRD, University of California, Los Angeles, California, Department of Zoology, University of California, Los Angeles, California, Department of Botanical Sciences, University of California, Los Angeles, California

Sweetpotato mitochondria, that showed respiratory control, were studied with respect to ultrastructure. If fixed in media containing sucrose at 0.4 M, the cristae were dilated and the matrix was highly condensed. A more orthodox ultrastructural form was observed when the mitochondria were fixed in a medium containing sucrose at 0.25 M, i.e., the matrix was more expanded, the cristae were less dilated, and peripherally, the inner membrane element lay adjacent to the outer membrane element. These results are discussed in terms of a sucrose-accessible space (space between outer and inner membrane elements including intracristal space), and a space relatively inaccessible to sucrose (matrix). Ultrastructural shifts were not observed with change in metabolic steady state of the mitochondria. High resolution electron micrographs showed that the ultrastructure of sweetpotato mitochondria is very similar to that of animal mitochondria.

Purity and homogeneity of mitochondrial fractions were followed both by phase-contrast and electron microscopy. Preparations from sweetpotato, using older methods, were relatively homogeneous with respect to particle type and size, whereas avocado preparations contained a high proportion of chloroplasts and cellular debris. A method of purification involving sucrose-density-gradient centrifugation was developed. Purified mitochondria exhibited respiratory control and appeared similar to unpurified mitochondria under the electron microscope.

³ Present address: Department of Anatomy, Karolinska Institutet, Stockholm, Sweden.

⁴ Present address: Department of Biology, Wright State University, Dayton, Ohio.

¹ Supported in part by research grants 5R01-GM-10487, and GM-08224 from the National Institutes of Health, and GB-2379 from the National Science Foundation.