Angelo Vianello

Plant Flavonoids—Biosynthesis, Transport and Involvement in Stress Responses

This paper aims at analysing the synthesis of flavonoids, their import and export in plant cell compartments, as well as their involvement in the response to stress, with particular reference to grapevine (Vitis vinifera L.). A multidrug and toxic compound extrusion (MATE) as well as ABC transporters have been demonstrated in the tonoplast of grape berry, where they perform a flavonoid transport. The involvement of a glutathione S-transferase (GST) gene has also been inferred. Recently, a putative flavonoid carrier, similar to mammalian bilitranslocase (BTL), has been identified in both grape berry skin and pulp. In skin the pattern of BTL expression increases from véraison to harvest, while in the pulp its expression reaches the maximum at the early ripening stage. Moreover, the presence of BTL in vascular bundles suggests its participation in long distance transport of flavonoids. In addition, the presence of a vesicular trafficking in plants responsible for flavonoid transport is discussed. Finally, the involvement of flavonoids in the response to stress is described.

Bioavailability of Flavonoids: A Review of Their Membrane Transport and the Function of Bilitranslocase in Animal and Plant Organisms

Fruits and vegetables are rich in flavonoids, and ample epidemiological data show that diets rich in fruits and vegetables confer protection against cardiovascular, neurodegenerative and inflammatory diseases, and cancer. However, flavonoid bioavailability is reportedly very low in mammals and the molecular mechanisms of their action are still poorly known. This review focuses on membrane transport of flavonoids, a critical determinant of their bioavailability. Cellular influx and efflux transporters are reviewed for their involvement in the absorption of flavonoids from the gastro-intestinal tract and their subsequent tissue distribution. A focus on the mammalian bilirubin transporter bilitranslocase (TCDB 2.A.65.1.1) provides further insight into flavonoid bioavailability and its relationship with plasma bilirubin (an endogenous antioxidant). The general function of bilitranslocase as a flavonoid membrane transporter is further demonstrated by the occurrence of a plant homologue in organs (petals, berries) where flavonoid biosynthesis is most active. Bilitranslocase appears associated with sub-cellular membrane compartments and operates as a flavonoid membrane transporter.

BMAP-28, an Antibiotic Peptide of Innate Immunity, Induces Cell Death through Opening of the Mitochondrial Permeability Transition Pore

ABSTRACT BMAP-28, a bovine antimicrobial peptide of the cathelicidin family, induces membrane permeabilization and death in human tumor cell lines and in activated, but not resting, human lymphocytes. In addition, we found that BMAP-28 causes depolarization of the inner mitochondrial membrane in single cells and in isolated mitochondria. The effect of the peptide was synergistic with that of Ca2+ and inhibited by cyclosporine, suggesting that depolarization depends on opening of the mitochondrial permeability transition pore. The occurrence of a permeability transition was investigated on the basis of mitochondrial permeabilization to calcein and cytochrome c release. We show that BMAP-28 permeabilizes mitochondria to entrapped calcein in a cyclosporine-sensitive manner and that it releases cytochrome c in situ. Our results demonstrate that BMAP-28 is an inducer of the mitochondrial permeability transition pore and that its cytotoxic potential depends on its effects on mitochondrial permeability.

Generation of superoxide anion and hydrogen peroxide at the surface of plant cells

AbstractIn addition to well-known cell wall peroxidases, there is now evidence for the presence of this enzyme at the plasma membrane of the plant cells (surface peroxidase). Both are able to catalyze, through a chain of reactions involving the superoxide anion, the oxidation of NADH to generate hydrogen peroxide. The latter is oxidized by other wall-bound peroxidases to convert cinnamoyl alcohols into radical forms, which, then polymerize to generate lignin. However, there are other enzymes at the surface of plasma membranes capable of generating hydrogen peroxide (cell wall polyamine oxidase), superoxide anion (plasma membrane Turbo reductase), or both (plasma membrane flavoprotein?). These enzymes utilize NAD(P)H as a substrate. The Turbo reductase and the flavoprotein catalyze the univalent reduction of Fe3+ and then of O2 to produce Fe2+ and

HYDROGEN PEROXIDE GENERATION BY HIGHER PLANT MITOCHONDRIA OXIDIZING COMPLEX I OR COMPLEX II SUBSTRATES

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NAD(P)H oxidation elicits anion superoxide formation in radish plasmalemma vesicles

, respectively. The superoxide anion, in the acidic environment of the cell wall, may then dismutate to H2O2. These superoxide anion- and hydrogen peroxide-generating systems are discussed in relation to their possible involvement in physiological and pathological processes in the apoplast of plant cells.

Guaiacol peroxidase associated to soybean root plasma membranes oxidizes ascorbate

Highly purified soybean (Glycine max L. Merr.) plasma membranes exhibit a lipoxygenase activity with a pH optimum in the acidic (5.5-6.0) range and with a Km value of 200 microM for both linolenic and linoleic acids. This activity is inhibited by nordihydroguaiaretic acid (NDGA), salicylhydroxamic acid (SHAM) and propyl gallate, stimulated by CaCl2 up to 0.25 mM, H2O2 (5 to 10 nM range) and by some nucleotide triphosphates (125 to 1000 nM range) in the following order ATP > GTP = UTP > CTP. The enzyme is not released by treatment of the membranes with 0.05% Brij 58 and its activity is approx. 65% inhibited by the impermeant p-chloromercuryphenyl-sulfonate only in 0.01% Triton X-100-treated membrane vesicles. These results indicate that soybean cells have an acid lipoxygenase, associated to the plasmalemma, with the catalytic site on the cytoplasmic surface. It may be distinguished from the soluble counterpart, because the latter is not stimulated by nucleotide triphosphates. The plasma membrane vesicles also show a lipoxygenase, active in the alkaline (9.0-9.5) range, inhibited by NDGA, SHAM and propyl gallate, stimulated by H2O2, but with a lower Km value (60 microM) and less sensitive to calcium stimulation than the acidic one. The possible involvement of acid lipoxygenase in senescence and in the response of plant cells to wounding and pathogen infection is discussed.

The mitochondrial permeability transition pore (PTP) — An example of multiple molecular exaptation?

The generation of H2O2 by isolated pea stem mitochondria, oxidizing either malate plus glutamate or succinate, was examined. The level of H2O2 was almost one order of magnitude higher when mitochondria were energized by succinate. The succinate‐dependent H2O2 formation was abolished by malonate, but unaffected by rotenone. The lack of effect of the latter suggests that pea mitochondria were working with a proton motive force below the threshold value required for reverse electron transfer. The activation by pyruvate of the alternative oxidase was reflected in an inhibition of H2O2 formation. This effect was stronger when pea mitochondria oxidized malate plus glutamate. Succinate‐dependent H2O2 formation was ca. four times lower in Arum sp. mitochondria (known to have a high alternative oxidase) than in pea mitochondria. An uncoupler (FCCP) completely prevented succinate‐dependent H2O2 generation, while it only partially (40–50%) inhibited that linked to malate plus glutamate. ADP plus inorganic phosphate (transition from state 4 to state 3) also inhibited the succinate‐dependent H2O2 formation. Conversely, that dependent on malate plus glutamate oxidation was unaffected by low and stimulated by high concentrations of ADP. These results show that the main bulk of H2O2 is formed during substrate oxidation at the level of complex II and that this generation may be prevented by either dissipation of the electrochemical proton gradient (uncoupling and transition state 4‐state 3), or preventing its formation (alternative oxidase). Conversely, H2O2 production, dependent on oxidation of complex I substrate, is mainly lowered by the activation of the alternative oxidase.