Intracellular signaling by diffusion: can waves of hydrogen peroxide transmit intracellular information in plant cells?

Amplitude- and frequency-modulated waves of Ca(2+) ions transmit information inside cells. Reactive Oxygen Species (ROS), specifically hydrogen peroxide, have been proposed to have a similar role in plant cells. We consider the feasibility of such an intracellular communication system in view of the physical and biochemical conditions in plant cells. As model system, we use a H(2)O(2) signal originating at the plasma membrane (PM) and spreading through the cytosol. We consider two maximally simple types of signals, isolated pulses and harmonic oscillations. First we consider the basic limits on such signals as regards signal origin, frequency, amplitude, and distance. Then we establish the impact of ROS-removing enzymes on the ability of H(2)O(2) to transmit signals. Finally, we consider to what extent cytoplasmic streaming distorts signals. This modeling allows us to predict the conditions under which diffusion-mediated signaling is possible. We show that purely diffusive transmission of intracellular information by H(2)O(2) over a distance of 1 μm (typical distance between organelles, which may function as relay stations) is possible at frequencies well above 1 Hz, which is the highest frequency observed experimentally. This allows both frequency and amplitude modulation of the signal. Signaling over a distance of 10 μm (typical distance between the PM and the nucleus) may be possible, but requires high signal amplitudes or, equivalently, a very low detection threshold. Furthermore, at this longer distance a high rate of enzymatic degradation is required to make signaling at frequencies above 0.1 Hz possible. In either case, cytoplasmic streaming does not seriously disturb signals. We conclude that although purely diffusion-mediated signaling without relaying stations is theoretically possible, it is unlikely to work in practice, since it requires a much faster enzymatic degradation and a much lower cellular background concentration of H(2)O(2) than observed experimentally

Massive gene loss in mistletoe (<em>Viscum</em>, Viscaceae) mitochondria

Parasitism is a successful survival strategy across all kingdoms and has evolved repeatedly in angiosperms. Parasitic plants obtain nutrients from other plants and some are agricultural pests. Obligate parasites, which cannot complete their lifecycle without a host, may lack functional photosystems (holoparasites), or have retained photosynthesis (hemiparasites). Plastid genomes are often reduced in parasites, but complete mitochondrial genomes have not been sequenced and their mitochondrial respiratory capacities are largely unknown. The hemiparasitic European mistletoe (Viscum album), known from folklore and postulated therapeutic properties, is a pest in plantations and forestry. We compare the mitochondrial genomes of three Viscum species based on the complete mitochondrial genome of V. album, the first from a parasitic plant. We show that mitochondrial genes encoding proteins of all respiratory complexes are lacking or pseudogenized raising several questions relevant to all parasitic plants: Are any mitochondrial gene functions essential? Do any genes need to be located in the mitochondrial genome or can they all be transferred to the nucleus? Can parasitic plants survive without oxidative phosphorylation by using alternative respiratory pathways? More generally, our study is a step towards understanding how host- and self-perception, host integration and nucleic acid transfer has modified ancestral mitochondrial genomes

Mitochondria in parasitic plants

Plant mitochondrial genomes are renowned for their structural complexity, extreme variation in size and mutation rates, and ability to incorporate foreign DNA. Parasitic flowering plants are no exception, and the close association between parasite and host may even enhance the likelihood of horizontal gene transfer (HGT) between them. Recent studies on mistletoes (Viscum) have revealed that these parasites have lost an exceptional number of mitochondrial genes, including all complex I genes of the respiratory chain. At the same time, an altered respiratory pathway has been demonstrated. Here we review the current understanding of mitochondrial evolution in parasitic plants with a special emphasis on HGT to and from parasite mitochondrial genomes, as well as the uniquely altered mitochondria in Viscum and related plants. © 2020 The Author

Structural Basis for Dityrosine-Mediated Inhibition of α-Synuclein Fibrillization

[Image: see text] α-Synuclein (α-Syn) is an intrinsically disordered protein which self-assembles into highly organized β-sheet structures that accumulate in plaques in brains of Parkinson’s disease patients. Oxidative stress influences α-Syn structure and self-assembly; however, the basis for this remains unclear. Here we characterize the chemical and physical effects of mild oxidation on monomeric α-Syn and its aggregation. Using a combination of biophysical methods, small-angle X-ray scattering, and native ion mobility mass spectrometry, we find that oxidation leads to formation of intramolecular dityrosine cross-linkages and a compaction of the α-Syn monomer by a factor of √2. Oxidation-induced compaction is shown to inhibit ordered self-assembly and amyloid formation by steric hindrance, suggesting an important role of mild oxidation in preventing amyloid formation

Isolation of Highly Purified, Intact, and Functional Mitochondria from Potato Tubers Using a Two-in-One Percoll Density Gradient

The isolation of mitochondria from potato tubers (Solanum tuberosum L.) is described, but the methodology can easily be adapted to other storage tissues. After homogenization of the tissue, filtration and differential centrifugation, the key step is a Percoll density gradient centrifugation. The Percoll gradient contains two parts: a bottom part containing Percoll in 0.3 M sucrose, and a slightly less dense top part containing Percoll in 0.3 M mannitol. After centrifugation, a density gradient is formed that is almost linear in the central part, and this is where the band containing the purified intact mitochondria is formed. This method makes it possible to process large amounts of plant material (2–6 kg) and saves at least 1.5 h on the preparation time compared to methods where two consecutive purification methods are used. Nonetheless, it yields large amounts of mitochondria (50–125 mg protein) of very high purity, intactness and functionality