Dispersal is a key process in determining the survival of plant species following habitat fragmentation and climate change, as well as driving the introduction and spread of invasive alien species in new regions. Due to its passive nature, seed dispersal is particularly complex, and the rare long-distance events relevant for plant species' responses to environmental change are a barrier to its understanding. Attempts to simplify the seed dispersal process often ignore dispersal by humans, despite the huge influence humans have over ecological systems throughout the world. In this Biodiversity Viewpoint, we describe how the movement patterns of humans and human-mediated dispersal vectors can be useful for understanding potential patterns of dispersal at multiple spatial scales. Humans and their associated dispersal vectors such as livestock and motor vehicles can disperse huge numbers of seeds of many plant species very long distances. Their relationships with the physical environment affect their movement, and therefore the movement of the seeds which they can potentially disperse. Therefore, we believe that a geographical approach can be useful at a time where understanding and managing pathways of dispersal are of direct relevance to the challenges faced by plant species and communities.

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Respiratory oxidases are transmembrane enzymes that catalyze the reduction of dioxygen to water in the final step of aerobic respiration. This process is linked to proton pumping across the membrane. Here, we developed a method to study the catalytic turnover of the quinol oxidase, cytochrome bo3 from E. coli at single‐molecule level. Liposomes with reconstituted cytochrome bo3 were loaded with a pH‐sensitive dye and changes in the dye fluorescence, associated with proton transfer and pumping, were monitored as a function of time. The single‐molecule approach allowed us to determine the orientation of cytochrome bo3 in the membrane; in ∼70 % of the protein‐containing liposomes protons were released to the outside. Upon addition of substrate we observed the buildup of a ΔpH (in the presence of the K+ ionophore valinomycin), which was stable over at least ∼800 s. No rapid changes in ΔpH (proton leaks) were observed during steady state proton pumping, which indicates that the free energy stored in the electrochemical gradient in E. coli is not dissipated or regulated through stochastic transmembrane proton leaks, as suggested from an earlier study (Li et al. J. Am. Chem. Soc. (2015) 137, 16055–16063).

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The transmembrane protein cytochrome c oxidase (CcO) is the terminal oxidase in the respiratory chain of many aerobic organisms and catalyzes the reduction of dioxygen to water. This process maintains an electrochemical proton gradient across the membrane hosting the oxidase. CcO is a well-established model enzyme in bioenergetics to study the proton-coupled electron transfer reactions and protonation dynamics involved in these processes. Its catalytic mechanism is subject to ongoing intense research. Previous research, however, was mainly focused on the turnover of oxygen and electrons in CcO, while studies reporting proton turnover rates of CcO, that is the rate of proton uptake by the enzyme, are scarce. Here, we reconstitute CcO from R. sphaeroides into liposomes containing a pH sensitive dye and probe changes of the pH value inside single proteoliposomes using fluorescence microscopy. CcO proton turnover rates are quantified at the single-enzyme level. In addition, we recorded the distribution of the number of functionally reconstituted CcOs across the proteoliposome population. Studies are performed using proteoliposomes made of native lipid sources, such as a crude extract of soybean lipids and the polar lipid extract of E. coli, as well as purified lipid fractions, such as phosphatidylcholine extracted from soybean lipids. It is shown that these lipid compositions have only minor effects on the CcO proton turnover rate, but can have a strong impact on the reconstitution efficiency of functionally active CcOs. In particular, our experiments indicate that efficient functional reconstitution of CcO is strongly promoted by the addition of anionic lipids like phosphatidylglycerol and cardiolipin.

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