title: Population heterogeneity of higher-plant mitochondria in structure and function.
abstract: Mitochondria of rapidly developing mungbean seedlings were fractionated into four populations: two density classes, each from a 1500S and a 150S pellet. Each of the four populations exhibited cytochrome c oxidase (COX) activity and contained mitochondrial DNA and cardiolipin; plastid and glyoxysome content were found to be relatively low. Five mitochondrial membrane proteins, COXII/III, ATPase alpha/beta and porin, and a matrix enzyme, manganese superoxide dismutase (MnSOD), were detected by immunoblots in all four populations. Another matrix enzyme, pyruvate dehydrogenase was detected only in the two respiratory-competent 1500S populations. The two 150S populations contained a previously unidentified organelle that lacked demonstrable respiratory capability. This organelle, which we have tentatively referred to as "slow-sedimenting (ss-) mitochondrion", was small in size (below light-optics resolution, 70-300nm, majority < or =200nm) and possessed a peculiar looking boundary membrane, ribosomes, and an occasional prominent electron-dense spot. Characteristically, ss-mitochondria were almost always in contact with a filament-aligned membrane-like structure of varying length. Cristae structure, while undetected in small ss-mitochondria, appeared in larger individuals. Typical mitochondria were found in the denser 1500S population, while the lighter 1500S population consisted of 300-800 nm mitochondria exhibiting a varying degree of size-dependent inner membrane folding. Using electron microscopy (EM) immunolocalization and serial sectioning, we have identified in situ organelles resembling in size and in fine structure the ss-mitochondria, which also exhibit a size-dependent folding of the inner membrane. These results suggest that small ss-mitochondria may undergo a progressive development in situ. Taken together, our findings demonstrate the existence of a pattern of structure-function-coordinated gross heterogeneity among mitochondria. This pattern of mitochondrial heterogeneity, characterized both in isolated mitochondria and in situ, implies that small ss-mitochondria may represent a type of "nascent mitochondria" derived from a yet unidentified mitochondria-propagation mode operating during rapid seedling growth. Mitochondrial division by binary fission, characterized by the appearance of dumbbell-shaped intermediates, was also detected.
authors.affiliation: Institute of Botany, Academia Sinica, Taipei, Taiwan, ROC.
authors.forename: H
authors.initials: H
authors.lastname: Dai
authors.forename: Y S
authors.initials: YS
authors.lastname: Lo
authors.forename: W N
authors.initials: WN
authors.lastname: Jane
authors.forename: L W
authors.initials: LW
authors.lastname: Lee
authors.forename: K S
authors.initials: KS
authors.lastname: Chiang
mesh_terms: D002308:Cardiolipins / Q000378:metabolism; D004272:DNA, Mitochondrial; D018744:DNA, Plant / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism; D007887:Fabaceae / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure; D018740:Genetic Heterogeneity; D008928:Mitochondria / Q000502:physiology* / Q000648:ultrastructure*; D015388:Organelles; D010940:Plant Proteins / Q000378:metabolism; D010946:Plants, Medicinal; D013329:Structure-Activity Relationship
chemical_list: D002308:Cardiolipins; D004272:DNA, Mitochondrial; D018744:DNA, Plant; D010940:Plant Proteins; D003576:Electron Transport Complex IV