ION UPTAKE BY PLANT MITOCHONDRIA

Histone inhibition of mitochondrial proton transport

Histone blocks proton uptake by mitochondria incubated in the presence of valinomycin or DNP. In the presence of DNP valinomycin-induced H+ uptake is not affected by histone. H+ uptake induced by nigericin is not affected by histone as well. Postulated mechanism of histone action involves the immobilization of proton translocation in mitochondrial membrane and induction of local change in H+ concentration, the prevention of the interaction between H+ and natural K+-carrier and Mg2+ transport system or valinomycin.

Phosphate-dependent Substrate Transport into Mitochondria: Oxidative Studies

The oxidation of malate and citrate by isolated plant mitochondria can be stimulated by the addition of inorganic phosphate. This stimulation (a) is not inhibited by oligomycin or uncouplers; (b) can not be duplicated by addition of adenine nucleotide; (c) is inhibited by 2-n-butylmalonate; and (d) is not evident in detergent-treated mitochondria. Phosphate was required to elicit uncoupler-stimulated respiration. It is concluded that these effects of phosphate are attributable to a stimulated rate of substrate penetration into the mitochondria, and do not involve the oxidative phosphorylation process.Disrupting the mitochondria with detergent removed the requirement for phosphate and showed that butylmalonate did not inhibit the respiratory enzymes.

Rapid Respiratory Changes Due to Red Light or Acetylcholine during the Early Events of Phytochrome-mediated Photomorphogenesis

Two millimeter long secondary root tips of etiolated mung bean (Phaseolus aureus) plants were given 4 minute consecutive treatments of darkness, red light, far red light, and acetylcholine during darkness. We studied the effects of these treatments on exogenous (H(+)) changes, ATP utilization, O(2) uptake, P(1) levels, and ATPase activity. Red light and acetylcholine increased the level of P(1), O(2) uptake, and exogenous H(+), but decreased ATP concentrations. Darkness and far red light caused the amount of ATP to increase and decreased the O(2) uptake and P(1) level. O(2) uptake of both excised root tips and isolated mitochondria was promoted by acetylcholine levels of the same order of magnitude that promoted the other photomimetic phenomena. ADP-O ratios indicated that acetylcholine did not cause an appreciable decrease in ATP synthesis. The total ATPase activity remained constant throughout all treatments. Ouabain caused no adhesion to negatively charged glass in the dark, while the inhibitors valinomycin, atractyloside, digitoxin, gramicidin, and oligomycin caused immediate adhesion. All of the inhibitors prevented release from the glass. In red light ouabain increased adhesion, whereas the other inhibitors caused caused immediate and complete adhesion.These data seem to imply that one of the functions of the phytochrome-mediated response to red light in roots, regulated by acetylcholine, is to cause the rapid utilization of ATP pools; far red light appears to inhibit this utilization.

A survey of the interaction of calcium ions with mitochondria from different tissues and species

A survey was made of the capacity of mitochondria isolated from a number of different tissues and species to accumulate Ca(2+) from the suspending medium during electron transport. The species examined included the rat, mouse, rabbit, hamster, guinea pig, cow, chicken, turtle, blowfly, yeast and Neurospora crassa. The tissues examined included vertebrate liver, kidney, brain, heart, spleen, thyroid and adrenal cortex, and the flight muscle of the blowfly. The mitochondria from all vertebrate tissues examined showed: (a) stimulation of State 4 respiration by added Ca(2+) (Ca(2+)/~ activation ratio about 2.0), accompanied by accumulation of Ca(2+) and ejection of H(+), with a H(+)/Ca(2+) ratio about 1.0; (b) a requirement of phosphate for accumulation of large amounts of Ca(2+); (c) respiration-independent high-affinity binding sites for Ca(2+); (d) endogenous Ca(2+), which is largely released by uncoupling agents. However, mitochondria from yeast and blowfly flight muscle are unable to accumulate Ca(2+) in a respiration-dependent process and possess no high-affinity Ca(2+)-binding sites. These findings support the view that the high-affinity sites represent the ligand-binding sites of a specific Ca(2+) ;permease' or transport system in the membrane. The relatively high affinity for Ca(2+), which equals or exceeds the affinity for ADP, and the generally uniform characteristics of Ca(2+) transport in all the vertebrate mitochondria tested strongly suggest that respiration-linked Ca(2+) accumulation plays a general and fundamental role in vertebrate cell physiology.