Development Of Mitochondrial Activities Research Articles

Effect of Benzyladenine on the Development of Mitochondrial Activities in Imbibed Black Gram Cotyledons

The development of mitochondria was followed in black gram cotyledons cultured on filter paper wetted with water or benzyladenine solution. Treatment with benzyladenine brought about an increase in activities of some mitochondrial enzymes and in respiratory activities of mitochondria. Cycloheximide did not inhibit the increase, although it almost completely inhibited the incorporation of (14)C-leucine into mitochondrial protein. It was inferred that the increase in mitochondrial activity by benzyladenine-treatment was not due to biogenesis of mitochondria but due to an acceleration of activation processes in pre-existing mitochondria. The respiratory control ratio of mitochondria from benzyladenine-treated cotyledons was lower than that of mitochondria from untreated ones. It was also suggested that benzyladenine brought about some qualitative changes in mitochondrial activities.

Influence of the axis on the development of mitochondrial activity in imbibed black gram cotyledons

The respiration rate of mitochondria from detached Vigna mungo L. cotyledons (without the embryonic axis) doubled during the first day after imbibition, whereas that of mitochondria from attached ones increased by only 50%. Contrary to the respiration rate, the respiratory control ratio was higher in attached cotyledons. The activities of enzymes in the mitochondrial fraction from detached cotyledons increased by about 30% during the first day, while those in mitochondria from attached ones changed little. Cycloheximide did not inhibit the development of mitochondrial respiration in either attached or detached cotyledons, although it almost completely inhibited the incorporation of [14C]‐leucine into mitochondrial proteins. Cycloheximide did not retard the increase in the activities of mitochondrial enzymes in detached cotyledons. It is inferred that the development of mitochondria in black gram cotyledons is brought about by repair or activation of mitochondria present in dry seeds and that the axis affects this repair process.

Biogenesis of Mitochondria in Imbibed Peanut Cotyledons: Influence of the Axis

Development of mitochondrial activities (state 3 respiration, respiratory control ratio, ADP/O ratio) in peanut cotyledons occurs over the first 5 d from the start of imbibition. Mitochondria in cotyledons with the axis attached develop better than in those from which the axis has been removed. Initially, mitochondria are deficient in cytochrome c, but after 2 d from the start of imbibition this deficiency is overcome. Mitochondrial development in attached cotyledons, as measured by state 3 respiration, respiratory control ratio, ADP/O ratio, and succinate dehydrogenase and cytochrome oxidase activities, is severely impaired by cycloheximide. This indicates that de novo synthesis of proteins is necessary for mitochondria and their enzymes to develop, a situation which is in sharp contrast to the situation in pea cotyledons. Electron microscope studies also show that there is an increase in the numbers of mitochondria in peanut cotyledons with time after the start of imbibition. Two patterns of mitochondrial development exist in legumes: in imbibed peanut cotyledons respiratory activities increase due to biogenesis of mitochondria, whereas in pea cotyledons the increases are due to improvement of pre-existing organelles.

Development of Mitochondrial Activities in Pea Cotyledons

Mitochondria in 4-hour imbibed and desiccated pea cotyledons develop in a similar manner upon rehydration to those in cotyledons hydrated only once. As a consequence of desiccation during imbibition, mitochondria revert to their original state as in the mature dry cotyledon, although limited damage occurs. This damage is more evident when the initial imbibition time before desiccation is longer. The presence of the axis does not protect cotyledonary mitochondria from damage, nor does it influence mitochondrial development upon rehydration of desiccated cotyledons. During the early hours after the start of imbibition mitochondrial development is dependent both upon hydration levels of the cotyledon and upon other metabolic processes, as shown by sensitivity to conditions that prevent ATP synthesis.

Development of Mitochondrial Activities in Pea Cotyledons during and following Germination of the Axis

Development of mitochondrial activities in pea cotyledons during early times after the start of imbibition occurred in two phases. In the first phase (0 to 8 hours after the start of imbibition), succinate or NADH oxidation increased rapidly, while malate or alpha-ketoglutarate oxidation remained low. The latter activities developed only 8 to 12 hours after the start of imbibition (the second phase). Development in the first phase was induced by water uptake, but some development occurred even when the cotyledons were fully imbibed. The presence of the axis was required for the second phase of the development. It is suggested that mitochondrial development in the second phase is brought about by activation of the electron transfer path at a site between the oxidation of endogenous NADH and the reduction of ubiquinone.

Development of Mitochondrial Activity in Pea Cotyledons Following Imbibition; Influence of the Embryonic Axis

The development of mitochondria in cotyledons during the initial stages following imbibition and the subsequent degeneration were faster when the embryonic axis was attached. This was more clearly demonstrated when mitochondrial activity was determined using malate or ct-oxo glutarate as substrate rather than NADH or succinate. Cycloheximide did not inhibit the initial development of mitochondria in attached cotyledons, although it inhibited the incorporation of l4C-amino acid into protein. Abscisic acid inhibited almost completely the initial increase in mitochondrial activities of attached cotyledons. The activities of several enzymes in mitochondrial fractions were almost the same in attached and detached cotyledons during 4 d after imbibition. The degeneration of mitochondria was not accompanied by the loss of enzymes. It was inferred that the initial development and the subsequent degeneration of mitochondria in cotyledons during 4 d after imbibition was brought about by the structural improvement and disorganiz ation of mitochondria, respectively. The initial differences in the development of mitochondrial activities between attached and detached cotyledons were suggested to be attributable to differences in the development of the activities of electron transfer pathway from endogenous NADH to ubiquinone.

Mitochondrial adenosine triphosphatase of the fission yeast, Schizosaccharomyces pombe 972h-. Changes in activity and oligomycin-sensitivity during the cell cycle of catabolite-repressed and -de-repressed cells.

1. Changes in activity of ATPase (adenosine triphosphatase) during the cell cycle of Schizosaccharomyces pombe were analysed in cell-free extracts of cells harvested from different stages of growth of synchronous cultures and also after cell-cycle fractionation. 2. Oligomycin-sensitive ATPase oscillates in both glucose-repressed synchronous cultures and shows four maxima of activity approximately equally spaced through the cell cycle. The amplitude of the oscillations accounts for between 13 and 80% of the total activity at different times in the cell cycle. 3. Oligomycin sensitivity varies over a fourfold range at different stages of the cell cycle. 4. The periodicity of maximum oligomycin sensitivity is one-quarter of a cell cycle. 5. These results were confirmed for the first three-quarters of the cell cycle by cell-cycle fractionation. 6. In cells growing synchronously with glycerol, ATPase activity increases in a stepwise pattern, with two steps per cell cycle; the first of these occurs at 0.54 of the cell cycle and the second at 0.95. 7. These results are discussed in relation to previously obtained data on the development of mitochondrial activities during the cell cycle.