New perspective for the upscaling of plant functional response to flooding stress in salt marshes using remote sensing

Understanding the response of salt marshes to flooding is crucial to foresee the fate of these fragile ecosystems, requiring an upscaling approach. In this study we related plant species and community response to multispectral indices aiming at parsing the power of remote sensing to detect the environmental stress due to flooding in lagoon salt marshes. We studied the response of Salicornia fruticosa (L.) L. and associated plant community along a flooding and soil texture gradient in nine lagoon salt marshes in northern Italy. We considered community (i.e., species richness, dry biomass, plant height, dry matter content) and individual traits (i.e., annual growth, pigments, and secondary metabolites) to analyze the effect of flooding depth and its interplay with soil properties. We also carried out a drone multispectral survey, to obtain remote sensing-derived vegetation indices for the upscaling of plant responses to flooding. Plant diversity, biomass and growth all declined as inundation depth increased. The increase of soil clay content exacerbated flooding stress shaping S. fruticosa growth and physiological responses. Multispectral indices were negatively related with flooding depth. We found key species traits rather than other community traits to better explain the variance of multispectral indices. In particular stem length and pigment content (i.e., betacyanin, carotenoids) were more effective than other community traits to predict the spectral indices in an upscaling perspective of salt marsh response to flooding. We proved multispectral indices to potentially capture plant growth and plant eco-physiological responses to flooding at the large scale. These results represent a first fundamental step to establish long term spatial monitoring of marsh acclimation to sea level rise with remote sensing. We further stressed the importance to focus on key species traits as mediators of the entire ecosystem changes, in an ecological upscaling perspective.

Characterisation and functionalisation of chitosan nanoparticles as carriers for double-stranded RNA (dsRNA) molecules towards sustainable crop protection

The need to minimise the impact of phytosanitary treatments for disease control boosted researchers to implement techniques with less environmental impact. The development of technologies using molecular mechanisms based on the modulation of metabolism by short dsRNA sequences appears promising. The intrinsic fragility of polynucleotides and the high cost of these techniques can be circumvented by nanocarriers that protect the bioactive molecule enabling high efficiency delivery to the leaf surface and extending its half-life. In this work, a specific protocol was developed aiming to assess the best methodological conditions for the synthesis of low-size chitosan nanoparticles (NPs) to be loaded with nucleotides. In particular, NPs have been functionalised with partially purified Green Fluorescent Protein dsRNAs (GFP dsRNA) and their size, surface charge and nucleotide retention capacity were analysed. Final NPs were also stained with FITC and sprayed on Nicotiana benthamiana leaves to assess, by confocal microscopy, both a distribution protocol and the fate of NPs up to 6 days after application. Finally, to confirm the ability of NPs to increase the efficacy of dsRNA interference, specific tests were performed: by means of GFP dsRNA-functionalised NPs, the nucleotide permanence during time was assessed both in vitro on detached wild-type N. benthamiana leaves and in planta; lastly, the inhibition of Botrytis cinerea on single leaves was also evaluated, using a specific fungal sequence (Bc dsRNA) as the NPs' functionalising agent. The encouraging results obtained are promising in the perspective of long-lasting application of innovative treatments based on gene silencing.

Contrasting Responses of Two Grapevine Cultivars to Drought: The Role of Non-structural Carbohydrates in Xylem Hydraulic Recovery

Xylem embolism is one of the possible outcomes of decreasing xylem pressure when plants face drought. Recent studies have proposed a role for non-structural carbohydrates (NSCs) in osmotic pressure generation, required for refilling embolized conduits. Potted cuttings of grapevine Grenache and Barbera, selected for their adaptation to different climatic conditions, were subjected to a drought stress followed by re-irrigation. Stem embolism rate and its recovery were monitored in vivo by X-ray micro-computed tomography (micro-CT). The same plants were further analyzed for xylem conduit dimension and NSC content. Both cultivars significantly decreased Ψpd in response to drought and recovered from xylem embolism after re-irrigation. However, although the mean vessel diameter was similar between the cultivars, Barbera was more prone to embolism. Surprisingly, vessel diameter was apparently reduced during recovery in this cultivar. Hydraulic recovery was linked to sugar content in both cultivars, showing a positive relationship between soluble NSCs and the degree of xylem embolism. However, when starch and sucrose concentrations were considered separately, the relationships showed cultivar-specific and contrasting trends. We showed that the two cultivars adopted different NSC-use strategies in response to drought, suggesting two possible scenarios driving conduit refilling. In Grenache, sucrose accumulation seems to be directly linked to embolism formation and possibly sustains refilling. In Barbera, maltose/maltodextrins could be involved in a conduit recovery strategy via the formation of cell-wall hydrogels, likely responsible for the reduction of conduit lumen detected by micro-CT.

Antifungal activity of chili pepper extract with potential for the control of some major pathogens in grapevine

BACKGROUND

In recent years, biofungicides have drawn increasing interest in vineyards for a more sustainable integrated and copper-limited pest management. Among alternatives, botanicals could represent valuable tools, being rich sources of biologically active compounds. Conversely to the well-known antioxidant and biological properties in relation to health benefits, investigation on bioactivity of hot pungent Capsicum sp. products against fungal phytopathogens in vineyards is still scarce. Therefore, the present study aimed at exploring the biologically active compounds profile of a chili pepper (Capsicum chinense Jacq.) pod extract and its antimicrobial properties against some of the major fungal and Oomycetes pathogens of grapevine, including Botrytis cinerea Pers., Guignardia bidwellii (Ellis) Viala & Ravaz and Plasmopara viticola (Berk. & M.A. Curtis) Berl. & De Toni.

RESULTS

The ethyl acetate-extracted oleoresin from the most pungent varieties was rich in capsaicinoids and polyphenols (371.09 and 268.5 μg mg-1 dry weight, respectively). Capsaicin and dihydrocapsaicin, hydroxycinnamic and hydroxybenzoic acids and quercetin derivatives were the most abundant, while carotenoids represented only a minor fraction. The oleoresin was efficient to inhibit all three pathogenic fungi and ED50 values were determined, evidencing that G. bidwellii was the more sensitive (0.233 ± 0.034 mg mL-1 ).

CONCLUSION

The results suggested a potentiality of chili pepper extract for the control of some important grapevine pathogens, their possible application being helpful for the recommended limitation in extensive use of copper in vineyard. The complex mixture of high amounts of capsaicinoids, associated to specific phenolic acids and other minor bioactive components might contribute to the observed antimicrobial action of chili pepper extract. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Plant growth shapes the effects of elevation on the content and variability of flavonoids in subalpine bilberry stands

The study of morphological and physiological responses of shrubs to climate is crucial for the understanding of future scenarios regarding climate change. In this light, studying shrub growth and physiological acclimation along an elevation gradient might be insightful. The phenolic metabolic pathway represents a powerful tool to interpret such processes. In the South-Eastern Alps, we investigated the relationships between elevation, plant traits (i.e. age, xylem ring width, annual shoot length), plant-plant interaction (i.e. shrub cover) and flavonoids in Vaccinium myrtillus L. (leaves, berries) in stands above the treeline. The relationships were parsed within causal networks using a confirmatory path analysis. Elevation was the main driver of V. myrtillus growth, having both direct and indirect effects on the leaf flavonoid content, but this was less evident for berries. In particular, the content of foliar flavonoids showed a peak at mid-elevation and where the growth of xylem rings was intermediate, while it decreased in stands with higher shoot length. Flavonoid content variability of both leaves and berries was affected by elevation and shoot length. In berries, flavonoid variability was further related to all growth traits and shrub cover. These findings evidence that flavonoid content is influenced by both elevation and growth traits of V. myrtillus, often showing non-linear relationships. These results suggest a trait-mediated response of this plant to climate conditions as a result of trade-offs between plant growth, plant defence, environmental stress and nutrient/resource availability.

Relationships between population traits, nonstructural carbohydrates, and elevation in alpine stands of Vaccinium myrtillus

PREMISE

Despite great attention given to the relationship between plant growth and carbon balance in alpine tree species, little is known about shrubs at the treeline. We hypothesized that the pattern of main nonstructural carbohydrates (NSCs) across elevations depends on the interplay between phenotypic trait plasticity, plant-plant interaction, and elevation.

METHODS

We studied the pattern of NSCs (i.e., glucose, fructose, sucrose, and starch) in alpine stands of Vaccinium myrtillus (above treeline) across an elevational gradient. In the same plots, we measured key growth traits (i.e., anatomical stem features) and shrub cover, evaluating putative relationships with NSCs.

RESULTS

Glucose content was positively related with altitude, but negatively related with shrub cover. Sucrose decreased at high altitude and in older populations and increased with higher percentage of vascular tissue. Starch content increased at middle and high elevations and in stands with high shrub cover. Moreover, starch content was negatively related with the number of xylem rings and the percentage of phloem tissue, but positively correlated with the percentage of xylem tissue.

CONCLUSIONS

We found that the increase in carbon reserves across elevations was uncoupled from plant growth, supporting the growth limitation hypothesis, which postulates NSCs accumulate at high elevation as a consequence of low temperature. Moreover, the response of NSC content to the environmental stress caused by elevation was buffered by phenotypic plasticity of plant traits, suggesting that, under climate warming conditions, shrub expansion due to enhanced plant growth would be pronounced in old but sparse stands.

Analysis of Non-Structural Carbohydrates and Xylem Anatomy of Leaf Petioles Offers New Insights in the Drought Response of Two Grapevine Cultivars

In grapevine, the anatomy of xylem conduits and the non-structural carbohydrates (NSCs) content of the associated living parenchyma are expected to influence water transport under water limitation. In fact, both NSC and xylem features play a role in plant recovery from drought stress. We evaluated these traits in petioles of Cabernet Sauvignon (CS) and Syrah (SY) cultivars during water stress (WS) and recovery. In CS, the stress response was associated to NSC consumption, supporting the hypothesis that starch mobilization is related to an increased supply of maltose and sucrose, putatively involved in drought stress responses at the xylem level. In contrast, in SY, the WS-induced increase in the latter soluble NSCs was maintained even 2 days after re-watering, suggesting a different pattern of utilization of NSC resources. Interestingly, the anatomical analysis revealed that conduits are constitutively wider in SY in well-watered (WW) plants, and that water stress led to the production of narrower conduits only in this cultivar.

The Possible Role of Non-Structural Carbohydrates in the Regulation of Tree Hydraulics

The xylem is a complex system that includes a network of dead conduits ensuring long-distance water transport in plants. Under ongoing climate changes, xylem embolism is a major and recurrent cause of drought-induced tree mortality. Non-structural carbohydrates (NSC) play key roles in plant responses to drought and frost stress, and several studies putatively suggest their involvement in the regulation of xylem water transport. However, a clear picture on the roles of NSCs in plant hydraulics has not been drawn to date. We summarize the current knowledge on the involvement of NSCs during embolism formation and subsequent hydraulic recovery. Under drought, sugars are generally accumulated in xylem parenchyma and in xylem sap. At drought-relief, xylem functionality is putatively restored in an osmotically driven process involving wood parenchyma, xylem sap and phloem compartments. By analyzing the published data on stem hydraulics and NSC contents under drought/frost stress and subsequent stress relief, we found that embolism build-up positively correlated to stem NSC depletion, and that the magnitude of post-stress hydraulic recovery positively correlated to consumption of soluble sugars. These findings suggest a close relationship between hydraulics and carbohydrate dynamics. We call for more experiments on hydraulic and NSC dynamics in controlled and field conditions.

Summer drought stress: differential effects on cane anatomy and non-structural carbohydrate content in overwintering Cabernet Sauvignon and Syrah vines

Grapevines store non-structural carbohydrates (NSC) during late summer to sustain plant development at the onset of the following spring’s growth. Starch is the main stored carbohydrate, found in the wood-ray parenchyma of roots and canes. Although the relationship between hydraulic and plant photosynthetic performance is well-recognized, little research has been done on the long-term effects of drought in grapevines adopting different strategies to cope with water stress (i.e. isohydric and anisohydric). We performed our study by exposing two different grape cultivars (Syrah and Cabernet Sauvignon) to a short but severe drought stress, at two stages of the growing season (July and September). No marked differences in the physiological and hydraulic responses of the two varieties were found, probably due to our experimental conditions. However, anatomical and biochemical characterization of overwintering canes pointed out several interesting outcomes. We found a significant and parallel increase of starch and medullar ray number in both cultivars exposed to early water stress. We hypothesize that stressed vines limited their carbon allocation to growth, while shifting it to starch accumulation, with a most evident effect in the period of intense photosynthetic activity. We also speculate that a different aptitude to osmotic adjustment may underlay variation in starch increase and the specific involvement of bark NSC in the two cultivars.

Caspase-3-like activity and proteasome degradation in grapevine suspension cell cultures undergoing silver-induced programmed cell death

Toxic metal contamination is one of the major environmental concerns of the recent decade, due to the large application of metals in industrial, healthcare and commercial products, even in the form of nanostructures and nanomaterials. Nevertheless, the effects of silver (Ag⁺) on plants have not yet thoroughly elucidated. Therefore, suspension cell cultures of grapevine were used as a model for investigating silver toxicity. To do this, oxidative stress and programmed cell death (PCD), evaluated as reactive oxygen species production, caspase-3-like activity and ubiquitin-proteasome system, were investigated. As a result, the highest concentration (10 μM) of Ag⁺ caused a rapid (within 24 h) induction of PCD (approx. 80%), accompanied by generation of reactive oxygen species and activation of caspase-3-like activity. In the presence of specific inhibitor of this enzyme, a partial recovery of cell viability and a strong inhibition of caspase-3-like activity was observed. In addition, silver-induced PCD was accompanied either by increase of poly-ubiquitin conjugated proteins and degradation of subunit PBA1 of the proteasome 20S core, similarly to what found for metal-induced neurotoxicity in animals. The present study shows that silver could induce PCD in grapevine suspension cell cultures, mediated by caspase-3-like activity and oxidative stress. These effects were associated to accumulation of poly-ubiquitin conjugated proteins, suggesting the impairment of ubiquitin-proteasome complex, confirmed by the decrease of the PBA1 subunit. These findings indicate that animal and plant cells could share a common pathway in response to toxic metal, which involves PCD and disassembling of proteasome complex.

Properties of the Permeability Transition of Pea Stem Mitochondria

In striking analogy with Saccharomyces cerevisiae, etiolated pea stem mitochondria did not show appreciable Ca²⁺ uptake. Only treatment with the ionophore ETH129 (which allows electrophoretic Ca²⁺ equilibration) caused Ca²⁺ uptake followed by increased inner membrane permeability, membrane depolarization and Ca²⁺ release. Like the permeability transition (PT) of mammals, yeast and Drosophila, the PT of pea stem mitochondria was stimulated by diamide and phenylarsine oxide and inhibited by Mg-ADP and Mg-ATP, suggesting a common underlying mechanism; yet, the plant PT also displayed distinctive features: (i) as in mammals it was desensitized by cyclosporin A, which does not affect the PT of yeast and Drosophila; (ii) similarly to S. cerevisiae and Drosophila it was inhibited by Pi, which stimulates the PT of mammals; (iii) like in mammals and Drosophila it was sensitized by benzodiazepine 423, which is ineffective in S. cerevisiae; (iv) like what observed in Drosophila it did not mediate swelling and cytochrome c release, which is instead seen in mammals and S. cerevisiae. We find that cyclophilin D, the mitochondrial receptor for cyclosporin A, is present in pea stem mitochondria. These results indicate that the plant PT has unique features and suggest that, as in Drosophila, it may provide pea stem mitochondria with a Ca²⁺ release channel.

'Last In-First Out': seasonal variations of non-structural carbohydrates, glucose-6-phosphate and ATP in tubers of two Arum species

Knowledge on the metabolism of polysaccharide reserves in wild species is still scarce. In natural sites we collected tubers of Arum italicum Mill. and A. maculatum L. - two geophytes with different apparent phenological timing, ecology and chorology - during five stages of the annual cycle in order to understand patterns of reserve accumulation and degradation. Both the entire tuber and its proximal and distal to shoot portion were utilised. Pools of non-structural carbohydrates (glucose, sucrose and starch), glucose-6-phosphate and ATP were analysed as important markers of carbohydrate metabolism. In both species, starch and glucose content of the whole tuber significantly increased from sprouting to the maturation/senescence stages, whereas sucrose showed an opposite trend; ATP and glucose-6-phosphate were almost stable and dropped only at the end of the annual cycle. Considering the two different portions of the tuber, both ATP and glucose-6-phosphate concentrations were higher in proximity to the shoot in all seasonal stages, except the flowering stage. Our findings suggest that seasonal carbon partitioning in the underground organ is driven by phenology and occurs independently of seasonal climate conditions. Moreover, our results show that starch degradation, sustained by elevated ATP and glucose-6-phosphate pools, starts in the peripheral, proximal-to-shoot portion of the tuber, consuming starch accumulated in the previous season, as a 'Last In-First Out' mechanism of carbohydrate storage.

Effects of prolonged drought on stem non-structural carbohydrates content and post-drought hydraulic recovery in Laurus nobilis L.: The possible link between carbon starvation and hydraulic failure

Drought-induced tree decline is a complex event, and recent hypotheses suggest that hydraulic failure and carbon starvation are co-responsible for this process. We tested the possible role of non-structural carbohydrates (NSC) content on post-drought hydraulic recovery, to verify the hypothesis that embolism reversal represents a mechanistic link between carbon starvation and stem hydraulics. Measurements were performed in laurel plants subjected to similar water stress levels either over short or long term, to induce comparable embolism levels. Plants subjected to mild and prolonged water shortage (S) showed reduced growth, adjustment of turgor loss point driven by changes in both osmotic potential at full turgor and bulk modulus of elasticity, a lower content of soluble NSC and a higher content of starch with respect to control (C) plants. Moreover, S plants showed a lower ability to recover from xylem embolism than C plants, even after irrigation. Our data suggest that plant carbon status might indirectly influence plant performance during and after drought via effects on xylem hydraulic functioning, supporting the view of a possible mechanistic link between the two processes.

Flavonoids and darkness lower PCD in senescing Vitis vinifera suspension cell cultures

BACKGROUND

Senescence is a key developmental process occurring during the life cycle of plants that can be induced also by environmental conditions, such as starvation and/or darkness. During senescence, strict control of genes regulates ordered degradation and dismantling events, the most remarkable of which are genetically programmed cell death (PCD) and, in most cases, an upregulation of flavonoid biosynthesis in the presence of light. Flavonoids are secondary metabolites that play multiple essential roles in development, reproduction and defence of plants, partly due to their well-known antioxidant properties, which could affect also the same cell death machinery. To understand further the effect of endogenously-produced flavonoids and their interplay with different environment (light or dark) conditions, two portions (red and green) of a senescing grapevine callus were used to obtain suspension cell cultures. Red Suspension cell Cultures (RSC) and Green Suspension cell Cultures (GSC) were finally grown under either dark or light conditions for 6 days.

RESULTS

Darkness enhanced cell death (mainly necrosis) in suspension cell culture, when compared to those grown under light condition. Furthermore, RSC with high flavonoid content showed a higher viability compared to GSC and were more protected toward PCD, in accordance to their high content in flavonoids, which might quench ROS, thus limiting the relative signalling cascade. Conversely, PCD was mainly occurring in GSC and further increased by light, as it was shown by cytochrome c release and TUNEL assays.

CONCLUSIONS

Endogenous flavonoids were shown to be good candidates for exploiting an efficient protection against oxidative stress and PCD induction. Light seemed to be an important environmental factor able to induce PCD, especially in GSC, which lacking of flavonoids were not capable of preventing oxidative damage and signalling leading to senescence.

In vivo assay to monitor flavonoid uptake across plant cell membranes

Flavonoids represent one of the most important molecules of plant secondary metabolism, playing many different biochemical and physiological roles. Although their essential role in plant life and human health has been elucidated by many studies, their subcellular transport and accumulation in plant tissues remains unclear. This is due to the absence of a convenient and simple method to monitor their transport. In the present work, we suggest an assay able to follow in vivo transport of quercetin, the most abundant flavonoid in plant tissues. This uptake was monitored using 2-aminoethoxydiphenyl borate (DPBA), a fluorescent probe, in non-pigmented Vitis vinifera cell cultures.

The Permeability Transition in Plant Mitochondria: The Missing Link

The synthesis of ATP in mitochondria is dependent on a low permeability of the inner membrane. Nevertheless, mitochondria can undergo an increased permeability to solutes, named permeability transition (PT) that is mediated by a permeability transition pore (PTP). PTP opening requires matrix Ca(2+) and leads to mitochondrial swelling and release of intramembrane space proteins (e.g., cytochrome c). This feature has been initially observed in mammalian mitochondria and tentatively attributed to some components present either in the outer or inner membrane. Recent works on mammalian mitochondria point to mitochondrial ATP synthase dimers as physical basis for PT, a finding that has been substantiated in yeast and Drosophila mitochondria. In plant mitochondria, swelling and release of proteins have been linked to programmed cell death, but in isolated mitochondria PT has been observed in only a few cases and in plant cell cultures only indirect evidence is available. The possibility that mitochondrial ATP synthase dimers could function as PTP also in plants is discussed here on the basis of the current evidence. Finally, a hypothetical explanation for the origin of PTP is provided in the framework of molecular exaptation.

Involvement of mammalian bilitranslocase-like protein(s) in chlorophyll catabolism of Pisum sativum L. tissues

Putative pea bilin and cyclic tetrapyrrole transporter proteins were identified by means of an antibody raised against a bilirubin-interacting aminoacidic sequence of mammalian bilitranslocase (TC No. 2.A.65.1.1). The immunochemical approach showed the presence of several proteins mostly in leaf microsomal, chloroplast and tonoplast vesicles. In these membrane fractions, electrogenic bromosulfalein transport activity was also monitored, being specifically inhibited by anti-bilitranslocase sequence antibody. Moreover, the inhibition of transport activity in pea leaf chloroplast vesicles, by both the synthetic cyclic tetrapyrrole chlorophyllin and the heme catabolite biliverdin, supports the involvement of some of these proteins in the transport of linear/cyclic tetrapyrroles during chlorophyll metabolism. Immunochemical localization in chloroplast sub-compartments revealed that these putative bilitranslocase-like transporters are restricted to the thylakoids only, suggesting their preferential implication in the uptake of cyclic tetrapyrrolic intermediates from the stroma during chlorophyll biosynthesis. Finally, the presence of a conserved bilin-binding sequence in different proteins (enzymes and transporters) from divergent species is discussed in an evolutionary context.

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.

Fulvic acid affects proliferation and maturation phases in Abies cephalonica embryogenic cells

Embryogenic cell masses (ECM) of Abies cephalonica were grown on proliferation media in the presence and absence of fulvic acid (FA), whose molecular composition and conformational rigidity were evaluated by CPMAS-¹³C NMR spectroscopy. To assess the physiological effects of this humic material during proliferation and maturation stages of somatic embryogenesis (SE), proliferation rate, proportion of consecutive developmental stages of pro-embryogenic masses (PEM), cellular ATP and glucose-6-phosphate were evaluated at regular intervals. FA increased the proliferation rate, especially during the early sampling days, and the percentage of PEM in their advanced developmental stage. Cellular ATP and glucose-6-phospahte were increased by FA pre-treatment during the maturation phase. Furthermore, the effects of the anti-auxin p-chlorophenoxyisobutyric acid (PCIB), such as a decrease of growth and the enhancement of PEM III induction, were inverted by FA. Proton pumping ATPase and PPase activities were decreased in microsomes from PCIB-treated ECM, while they increased in the presence of FA. This fulvic matter also induced a delay in somatic embryo formation during the maturation phase. Both the improvement of the PEM proliferation and the reduction of the subsequent maturation process of A. cephalonica are explained by a release from the complex humic structure of low molecular-weight molecules, which may interact with the plant hormonal signaling pathway. These effects appear to be related to the hydrophilic and conformationally labile nature of FA. The structure-activity relationship observed here suggests that the influence of FA on ECM may be attributed to specific bioactive molecules that are preferentially released from the FA loose superstructure.

Electrogenic bromosulfalein transport in isolated membrane vesicles: implementation in both animal and plant preparations for the study of flavonoid transporters

Bromosulfalein is an organic anion dye used in the study of a variety of membrane carriers expressed in animal tissues and involved in transport of drugs and metabolites. The spectrophotometric assay of electrogenic bromosulfalein transport in membrane vesicles, isolated from various mammalian organs or tissues, enables to specifically measure the transport activity of bilitranslocase (TCDB 2.A.65.1.1). The latter is a bilirubin- and flavonoid-specific transporter expressed in rat liver, the organ where its function has been best characterized. The spectrophotometric assay of electrogenic bromosulfalein transport requires minimal volumes of membrane vesicles, is completed within 1 min, and, therefore, is a useful tool to screen the transporter spectrum of potential substrates, by testing them as reversible inhibitors of bromosulfalein transport kinetics. Furthermore, the assay enables to study the progress of time-dependent inactivation of bromosulfalein transport, caused by different protein-specific reagents, including specific anti-sequence antibodies. Inactivation can be retarded by the presence of substrates in a concentration-dependent manner, enabling to derive the dissociation constants of the transporter-substrate complex and thus to gain further insight into the transporter structure-function relationship. This assay, implemented in membrane vesicles isolated from plant organs, has paved the way to the discovery of homologues of bilitranslocase in plants.

Mitochondrial bioenergetics linked to the manifestation of programmed cell death during somatic embryogenesis of Abies alba

The present work reports changes in bioenergetic parameters and mitochondrial activities during the manifestation of two events of programmed cell death (PCD), linked to Abies alba somatic embryogenesis. PCD, evidenced by in situ nuclear DNA fragmentation (TUNEL assay), DNA laddering and cytochrome c release, was decreased in maturing embryogenic tissue with respect to the proliferation stage. In addition, the major cellular energetic metabolites (ATP, NAD(P)H and glucose-6-phosphate) were highered during maturation. The main mitochondrial activities changed during two developmental stages. Mitochondria, isolated from maturing, with respect to proliferating cell masses, showed an increased activity of the alternative oxidase, external NADH dehydrogenase and fatty-acid mediated uncoupling. Conversely, a significant decrease of the mitochondrial K (ATP)(+) channel activity was observed. These results suggest a correlation between mitochondrial activities and the manifestation of PCD during the development of somatic embryos. In particular, it is suggested that the K (ATP)(+) channel activity could induce an entry of K(+) into the matrix, followed by swelling and a release of cytochrome c during proliferation, whereas the alternative pathways, acting as anti-apoptotic factors, may partially counteract PCD events occurring during maturation of somatic embryos.

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.

Identification and localization of the bilitranslocase homologue in white grape berries (Vitis vinifera L.) during ripening

A homologue of the mammalian bilirubin transporter bilitranslocase (BTL) (TCDB 2.A.65.1.1), able to perform an apparent secondary active transport of flavonoids, has previously been found in carnation petals and red grape berries. In the present work, a BTL homologue was also shown in white berries from Vitis vinifera L. cv. Tocai/Friulano, using anti-sequence antibodies specific for rat liver BTL. This transporter, similarly to what found in red grape, was localized in the first layers of the epidermal tissue and in the vascular bundle cells of the mesocarp. In addition, a strong immunochemical reaction was detected in the placental tissue and particularly in peripheral integuments of the seed. The protein was expressed during the last maturation stages in both skin and pulp tissues and exhibited an apparent molecular mass of c. 31 kDa. Furthermore, the transport activity of such a carrier, measured as bromosulphophthalein (BSP) uptake, was detected in berry pulp microsomes, where it was inhibited by specific anti-BTL antibodies. The BTL homologue activity exhibited higher values, for both K(m) and V(max), than those found in the red cultivar. Moreover, two non-pigmented flavonoids, such as quercetin (a flavonol) and eriodictyol (a flavanone), inhibited the uptake of BSP in an uncompetitive manner. Such results strengthen the hypothesis that this BTL homologue acts as a carrier involved also in the membrane transport of colourless flavonoids and demonstrate the presence of such a carrier in different organs and tissues.

Activity of a KATP+ channel in Arum spadix mitochondria during thermogenesis

This report demonstrates that mitochondria isolated from thermogenic Arum spadices possess an ATP-sensitive potassium channel--responsible for electrical potential (DeltaPsi) collapse and mitochondrial swelling--whose characteristics are similar to those previously described in pea and wheat mitochondria. In order to study the relationship between this K(ATP)(+) channel and the uncoupled respiration, linked to thermogenesis, K(+) transport activities were compared with those of mitochondria that were isolated from pea stems, soybean suspension cell cultures and Arum tubers. The channel from Arum spadices is highly active and its major features are (i) potassium flux is performed primarily in an inward-rectifying manner; (ii) the influx of K(+) is associated with a matrix volume increase in both energized and non-energized mitochondria; and (iii) its activity depends on the redox state of electron transport chain (ETC) and oxygen availability. In particular, this paper shows that the K(ATP)(+) channel is inwardly activated in parallel with the alternative oxidase (AO). The activation is linked to an ETC-oxidized state and to high oxygen consumption. The putative role of this K(ATP)(+) channel is discussed in relation to flowering of thermogenic Arum spadices.

Transport and accumulation of flavonoids in grapevine (Vitis vinifera L.)

Flavonoids are a group of secondary metabolites widely distributed in plants that represent a huge portion of the soluble phenolics present in grapevine (Vitis vinifera L.). These compounds play different physiological roles and are often involved in protection against biotic and abiotic stress. Even if the flavonoid biosynthetic pathways have been largely characterized, the mechanisms of their transport and accumulation in cell wall and vacuole are still not completely understood. This review analyses the known mechanisms of flavonoid uptake and accumulation in grapevine, with reference to the transport models and membrane carrier proteins described in other plant species. The effect of different environmental factors on flavonoid biosynthesis and transporters is also discussed.

Evidence for a putative flavonoid translocator similar to mammalian bilitranslocase in grape berries (Vitis vinifera L.) during ripening

During maturation, Vitis vinifera berries accumulate a large amount of several anthocyanins in the epidermal tissue, whereas their precursors and intermediates are ubiquitously synthesized within the fruit. Up to date, several mechanisms of flavonoid transport at subcellular level have been hypothesized, but it is not possible to identify a general model applicable in every plant tissue and organ. Recently, a putative anthocyanin carrier, homologue to mammalian bilitranslocase (BTL) (TC 2.A.65.1.1), was found in Dianthus caryophyllus petal microsomes. In the present paper, an immunohistochemical and immunochemical analysis, using an antibody raised against a BTL epitope, evidences the expression and function of such a transporter in V. vinifera berries (cv. Merlot). Specific localisations of the putative carrier within berry tissues together with expression changes during different developmental stages are shown. Water stress induces an increase in protein expression in both skin and pulp samples. A bromosulfalein (BSP) uptake activity, inhibitable by the BTL antibody, is detected in berry mesocarp microsomes, with K (m) = 2.39 microM BSP and V (max) = 0.29 micromol BSP min(-1) mg(-1) protein. This BSP uptake is also competitively inhibited by quercetin (K (i) = 4 microM). A putative role for this carrier is discussed in relation to the membrane transport of secondary metabolites.

Isolation of mitochondria from embryogenic cultures of Picea abies (L.) Karst. and Abies cephalonica Loud.: characterization of a K+(ATP) channel

A valuable method to isolate and purify mitochondria from embryonal masses of two coniferous species (Picea abies [L.] Karst. and Abies cephalonica Loud.) is described. Crude mitochondria from both species were shown to be intact, oxygen consuming (with malate plus glutammate, succinate and NADH as substrates) and well coupled (respiratory control ratio ca. 4). The oxidation of the substrates was only partially KCN-insensitive (alternative oxidase) in some cases. However, these fractions were contaminated by membranes (e.g. plasmalemma, tonoplast, Golgi and endoplasmic reticulum). After purification by a discontinuous Percoll gradient (18, 23, 40%, v/v), three mitochondrial populations were separated. The 0/18 interface fraction was composed mainly of broken and uncoupled mitochondria, while the other two (18/23 and 23/40 interface fractions) contained intact and coupled mitochondria, but only 23/40 interface fraction revealed to be better purified starting from both coniferous embryonal masses. In the latter purified fraction, the presence of a cyclosporin A-sensitive K (ATP) (+) channel was demonstrated. These findings were discussed in the light of the potential use of these mitochondrial fractions in bioenergetic studies, or in the involvement of these organelles to stress response in conifers.

The K(ATP)+ channel is involved in a low-amplitude permeability transition in plant mitochondria

Pea (Pisum sativum) stem mitochondria, energized by NADH, succinate or malate plus glutamate, underwent a spontaneous low-amplitude permeability transition (PT), which could be monitored by dissipation of the electrical potential (deltapsi) or swelling. The occurrence of the latter effects was dependent on O2 availability, because O2 shortage anticipated the manifestation of both deltapsi dissipation and swelling. Spontaneous deltapsi collapse was also monitored in sucrose-resuspended mitochondria and again O2 deprivation caused an anticipation of the phenomenon. However, in this case deltapsi dissipation was not accompanied by a parallel mitochondrial swelling. The latter effect was, indeed, evident only if mitochondria were resuspended in KCl (as osmoticum), or other cations with a molecular mass up to 100 Da (choline+). PT was also induced by protonophores (carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) or free fatty acids) or valinomycin (only in KCl). The FCCP-induced dissipation of deltapsi and swelling were inhibited by ATP and stimulated (anticipated) by cyclosporin A or O2 shortage. The FCCP-induced PT was accompanied by the release of pyridine nucleotides from the matrix and of cytochrome c from the intermembrane space of KCl-resuspended mitochondria. The spontaneous and FCCP-induced low-amplitude PT of plant mitochondria are interpreted as due to the activity of a recently identified K(ATP)+ channel whose open/closed state is dependent on polarization of the inner membrane and on the oxidoreductive state of some sulfhydryl groups.

Characterization of electrogenic bromosulfophthalein transport in carnation petal microsomes and its inhibition by antibodies against bilitranslocase

Bilitranslocase is a rat liver plasma membrane carrier, displaying a high-affinity binding site for bilirubin. It is competitively inhibited by grape anthocyanins, including aglycones and their mono- and di-glycosylated derivatives. In plant cells, anthocyanins are synthesized in the cytoplasm and then translocated into the central vacuole, by mechanisms yet to be fully characterized. The aim of this work was to determine whether a homologue of rat liver bilitranslocase is expressed in carnation petals, where it might play a role in the membrane transport of anthocyanins. The bromosulfophthalein-based assay of rat liver bilitranslocase transport activity was implemented in subcellular membrane fractions, leading to the identification of a bromosulfophthalein carrier (K(M) = 5.3 microm), which is competitively inhibited by cyanidine 3-glucoside (Ki = 51.6 microm) and mainly noncompetitively by cyanidin (Ki = 88.3 microm). Two antisequence antibodies against bilitranslocase inhibited this carrier. In analogy to liver bilitranslocase, one antibody identified a bilirubin-binding site (Kd = 1.7 nm) in the carnation carrier. The other antibody identified a high-affinity binding site for cyanidine 3-glucoside (Kd = 1.7 microm) on the carnation carrier only, and a high-affinity bilirubin-binding site (Kd = 0.33 nm) on the liver carrier only. Immunoblots showed a putative homologue of rat liver bilitranslocase in both plasma membrane and tonoplast fractions, isolated from carnation petals. Furthermore, only epidermal cells were immunolabeled in petal sections examined by microscopy. In conclusion, carnation petals express a homologue of rat liver bilitranslocase, with a putative function in the membrane transport of secondary metabolites.

Involvement of the mitochondrial K(+)ATP channel in H2O2- or NO-induced programmed death of soybean suspension cell cultures

Soybean suspension cell cultures were treated by H2O2 or nitric oxide (NO), to assess the mechanism leading to programmed cell death (PCD). Hydrogen peroxide (5 mM) induced PCD. Cells become necrotic at 20 mM H2O2, with cells exhibiting intermediate hallmarks before that (necrapoptotic cells). The level of ATP and of glucose-6-phosphate remained constant in cells undergoing PCD, while it decreased significantly in the necrotic ones. Mitochondria, isolated from 5 mM H2O2-treated (apoptotic) cells, showed that succinate-dependent oxygen consumption was slightly uncoupled, and the electrical potential difference (delta psi) weakly decreased. The addition of KCl to the delta psi formed determined a partial dissipation, which was higher than the dissipation observed in mitochondria from control cells. The addition of cyclosporin A (CsA) to de-energized mitochondria also induced delta psi formation, due to a K+ efflux from the matrix, which was decreased in mitochondria from treated cells. The same pattern of response was also observed in mitochondria isolated from 1 mM sodium nitroprusside (NO)-treated cells, exhibiting apoptotic symptoms. In mitochondria isolated from 20 mM H2O2-treated (necrotic) cells, succinate-dependent oxygen consumption was completely uncoupled, delta psi generation significantly inhibited, and CsA-dependent delta psi formation prevented. In addition, mitochondria isolated from control cells still underwent swelling, which was partially or completely prevented in mitochondria isolated from apoptotic or necrotic cells, respectively. The moderate swelling was accompanied by a slight rupture of the outer membrane and by a release of cytochrome c. These results point to the involvement of a K(+)ATP channel during the manifestation of PCD induced by H2O2 or NO in plants.

Biochemical and immunochemical evidences for the presence of lipoxygenase in plant mitochondria

In this paper, both biochemical and immunochemical evidence for the presence of lipoxygenase (LOX) in plant mitochondria is presented. Highly purified pea (Pisum sativum L., cv. Alaska) mitochondria show LOX activity, evaluated as conjugated diene formation, oxygen consumption, and hydroperoxide formation. Both 9- and 13-hydroperoxy-octadecadienoic acids are produced by the oxidation of linoleic acid. LOX activity is particularly evident in swollen mitochondria; it is inhibited by nordihydroguaiaretic acid, a pea anti-LOX B antibody, and has two pH optima (6.0 and 7.5). A mitochondrial protein of approximately 97 kDa cross-reacts with a pea seed anti-LOX B antibody. This reaction is detectable in both soluble (matrix fraction) and membrane-bound (submitochondrial particles) proteins. Considering that pea mitochondria were extracted from actively growing stems that were differentiating tube elements, it is suggested that the presence of LOX in these organelles may be related to their degradation linked to xylem differentiation.

Modulation of a plant mitochondrial K+ATP channel and its involvement in cytochrome c release

Pea stem mitochondria, resuspended in a KCl medium (de-energized mitochondria), underwent a swelling, as a consequence of K+ entry, that was inhibited by ATP. This inhibition was partially restored by GTP and diazoxide (K+ATP channel openers). In addition, glyburide and 5-hydroxydecanate (K+ATP channel blockers) induced an inhibition of the GTP-stimulated swelling. Mitochondrial swelling was inhibited by H2O2, but stimulated by NO. The same type of responses was also obtained in succinate-energized mitochondria. When the succinate-dependent transmembrane electrical potential (deltapsi) had reached a steady state, the addition of KCl induced a dissipation that was inhibited by H2O2 and stimulated by NO. The latter stimulation was prevented by carboxy-PTIO, a NO scavenger. Phenylarsine oxide (a thiol oxidant) and NEM (a thiol blocker) stimulated the KCl-induced dissipation of deltapsi, while DTE prevented this effect in both cases. In addition, DTE transiently inhibited the NO-induced dissipation of deltapsi, but then it caused a more rapid collapse. These results, therefore, show that the plant mitochondrial K+ATP channel resembles that present in mammalian mitochondria and that it appears to be modulated by dithiol-disulfide interconversion, NO and H2O2. The aperture of this channel was linked to the partial rupture of the outer membrane. The latter effect led to a release of cytochrome c, thus suggesting that this release may be involved in the manifestation of programmed cell death.

Cyclosporin A induces the opening of a potassium-selective channel in higher plant mitochondria

The immunosuppressive drug, cyclosporin A (CsA), induces the generation of a transmembrane electrical potential difference (deltapsi) in deenergized plant mitochondria incubated in sucrose-based media. Build up of deltapsi is prevented by external monovalent cations in the order K+ > Rb+ = Li+ > Na+, or by the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone, which also collapses the deltapsi generated by CsA. Entry of K+ into mitochondria can be monitored as swelling by incubating the organelles in a medium containing KCl to maintain constant osmolarity. This swelling is inhibited by ATP and stimulated by CsA or valinomycin. In addition, in mitochondria energized by succinate, KCl causes a dissipation of deltapsi, with sigmoidal kinetics, which is favored by CsA. Therefore, plant mitochondria appear to possess a K+ selective, voltage-dependent channel, which is opened by CsA, regulated by the redox state, and inhibited by nucleotides. The hypothetical roles of this new K+ATP channel are discussed in relation to its potential involvement in mitochondrial volume regulation, thermogenesis, apoptosis, and/or prevention of reactive oxygen species formation in plants.

Hydrogen peroxide generation by higher plant mitochondria oxidizing complex I or complex II substrates

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.

Zearalenone-induced uncoupling in plant mitochondria is sensitive to 6-ketocholestanol

Zearalenone (F-2) is a mycotoxin which acts as a protonophoric uncoupler in plant mitochondria [Macri, F. and Vianello, A., (1990) J. Plant Physiol. 136, 754-757]. In the present paper, the mechanism of F-2-induced uncoupling in pea mitochondria was studied. The uncoupling by F-2 was partially reversed by 6-ketocholestanol (kCh) under conditions in which kCh completely reversed the FCCP-induced uncoupling and almost did not affect the palmitate-induced uncoupling. Recoupling effects of carboxyatractylate, ADP and cyclosporin A were small and could not essentially decrease the kCh-insensitive part of F-2-induced uncoupling. It is suggested that a protein, mediating kCh-sensitive uncoupling, is involved in the F-2 effect in plant mitochondria.

Lipoxygenase activity associated to isolated soybean plasma membranes

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.

Effect of carboxyatractylate on transmembrane electrical potential of plant mitochondria in different metabolic states

The effects of carboxyatractylate (CAtr) on delta psi in sunflower hypocotyl and pea stem mitochondria were compared. In sunflower mitochondria, (1) CAtr at higher concentration increased delta psi in the presence of palmitate and delta psi in metabolic state 3; (2) ]1 microM CAtr did not prevent delta psi decrease, induced by ADP addition (in contrast to pea mitochondria); (3) The ATP-generated delta psi was small and was insensitive to 40 microM CAtr. Under the same conditions, in pea mitochondria generation of delta psi by ATP was inhibited by 1 microM CAtr.

ATP/ADP antiporter is involved in uncoupling of plant mitochondria induced by low concentrations of palmitate

Carboxyatractyloside partially restored the transmembrane electrical potential difference (delta psi) dissipated by low concentrations of palmitate in pea stem mitochondria. This effect was more marked when mitochondria from sunflower were assayed. It is suggested that the ATP/ADP translocator is involved in the free fatty acid-induced uncoupling of oxidative phosphorylation in plant mitochondria, only when its level is sufficiently high and the concentration of the fatty acid is low to collapse only partially the delta psi.

ATP/ADP antiporter is involved in uncoupling of plant mitochondria induced by low concentrations of palmitate

Carboxyatractyloside partially restored the transmembrane electrical potential difference (delta psi) dissipated by low concentrations of palmitate in pea stem mitochondria. This effect was more marked when mitochondria from sunflower were assayed. It is suggested that the ATP/ADP translocator is involved in the free fatty acid-induced uncoupling of oxidative phosphorylation in plant mitochondria, only when its level is sufficiently high and the concentration of the fatty acid is low to collapse only partially delta psi.

Electrical potential dissipation induced by free fatty acids in pea stem mitochondria

Linolenic, linoleic, oleic, palmitic and stearic acids (FFA) collapse the electrical potential of pea stem mitochondria in the absence or in the presence of 0.5 mM Mg2+. Higher concentrations of this cation (5 mM) lower the rate of dissipation caused by linoleic, oleic and palmitic acids, while abolishing that induced by stearic acid. Carboxyatractyloside and ADP do not reverse the FFA-induced collapse both in the presence or absence of Mg2+. EDTA, EGTA or BHT do not influence the dissipation caused by FFA that, in addition, is not linked to lipid peroxidation evaluated as malondialdehyde or conjugated diene formation. Only linolenic acid sustains a peroxidation which, however, appears to be caused by its own oxidation catalysed by lipoxygenases rather than by membrane lipoperoxidation induced by this free fatty acid. These results suggest that neither the ATP/ADP exchanger nor lipid peroxidation appear to be involved in FFA-induced uncoupling in pea stem mitochondria.