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The maintenance of hydraulic function during and after a drought event is crucial for tree survival, but the importance of non-structural carbohydrates (NSCs) in the recovery phase is still debated. We tested whether higher NSC availability facilitates post-drought hydraulic recovery, by applying a short-term drought (S dr) and a long-term drought combined with shading (L dr+sh) in Fraxinus ornus and Ostrya carpinifolia. Plants were then re-irrigated and recovery was checked 24 h later, by measuring water potential, stem percentage loss of hydraulic conductance (PLC) and NSC content. The relative magnitude of hydraulic and carbon constraints was also assessed in desiccated plants. During drought, PLC increased only in F. ornus, while it was maintained almost constant in O. carpinifolia due to tighter stomatal control of xylem pressure (i.e. more isohydric). In F. ornus , only S dr plants maintained high NSC contents at the end of drought and, when re-irrigated, recovered PLC to control values. Whereas hydraulic failure was ubiquitous, only F. ornus depleted NSC reserves at mortality. Our results suggest that preserving higher NSC content at the end of a drought can be important for the hydraulic resilience of trees. • Drought induces hydraulic failure and carbon starvation. • Hydraulic recovery was possible only in plants with high carbohydrate content. • Carbon starvation was not an ubiquitous cause of plant mortality. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recent reports on tree mortality associated with anomalous drought and heat have raised interest into processes underlying tree resistance/resilience to water stress. Hydraulic failure and carbon starvation have been proposed as main causes of tree decline, with recent theories treating water and carbon metabolism as interconnected processes. We subjected young plants of two native ( Quercus pubescens [Qp] and Prunus mahaleb [Pm]) and two invasive ( Robinia pseudoacacia [Rp] and Ailanthus altissima [Aa]) woody angiosperms to a prolonged drought leading to stomatal closure and xylem embolism, to induce carbon starvation and hydraulic failure. At the end of the treatment, plants were measured for embolism rates and NSC content, and re-irrigated to monitor recovery of xylem hydraulics. Data highlight different hydraulic strategies in native vs invasive species under water stress, and provide physiological explanations for species-specific impacts of recent severe droughts. Drought-sensitive species (Qp and Rp) suffered high embolism rates and were unable to completely refill xylem conduits upon restoration of water availability. Species that better survived recent droughts were able to limit embolism build-up (Pm) or efficiently restored hydraulic functionality after irrigation (Aa). Species-specific capacity to reverse xylem embolism correlated to stem-level concentration of soluble carbohydrates, but not to starch content. [ABSTRACT FROM AUTHOR]

Abstract: The mitochondrial permeability transition (PT) is a well-recognized phenomenon that allows mitochondria to undergo a sudden increase of permeability to solutes with molecular mass ≤1500Da, leading to organelle swelling and structural modifications. The relevance of PT relies on its master role in the manifestation of programmed cell death (PCD). This function is performed by a mega-channel (in some cases inhibited by cyclosporin A) named permeability transition pore (PTP), whose function could derive from the assembly of different mitochondrial proteins. In this paper we examine the distribution and characteristics of PTP in mitochondria of eukaryotic organisms so far investigated in order to draw a hypothesis on the mechanism of its evolution. As a result, we suggest that PTP may have arisen as a new function linked to a multiple molecular exaptation of different mitochondrial proteins, even though they could nevertheless still play their original role. Furthermore, we suggest that the early appearance of PTP could have had a crucial role in the establishment of endosymbiosis in eukaryotic cells, by the coordinated balancing of ATP production by glycolysis (performed by the primary phagocyte) and oxidative phosphorylation (accomplished by the endosymbiont). Indeed, we argue on the possibility that this new energetic equilibrium could have opened the way to the subsequent evolution toward metazoans. [Copyright &y& Elsevier]

Summary: This report demonstrates that mitochondria isolated from thermogenic Arum spadices possess an ATP-sensitive potassium channel – responsible for electrical potential (ΔΨ) 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 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 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 channel is discussed in relation to flowering of thermogenic Arum spadices. [Copyright &y& Elsevier]

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 (ΔΨ) or swelling. The occurrence of the latter effects was dependent on O2 availability, because O2 shortage anticipated the manifestation of both ΔΨ dissipation and swelling. Spontaneous ΔΨ collapse was also monitored in sucrose-resuspended mitochondria and again O2 deprivation caused an anticipation of the phenomenon. However, in this case ΔΨ 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 ΔΨ 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 KATP+ channel whose open/closed state is dependent on polarization of the inner membrane and on the oxidoreductive state of some sulfhydryl groups. [Copyright &y& Elsevier]

A soluble protein with a molecular mass of 55 kDa has been purified from etiolated pea stem mitochondria. The protein exhibits a Mg2+-requiring PPiase activity, with an optimum at pH 9.0, which is not stimulated by monovalent cations, but inhibited by F−, Ca2+, aminomethylenediphosphate and imidodiphosphate. The protein does not cross-react with polyclonal antibodies raised against vacuolar, mitochondrial or soluble PPiases, respectively. Conversely, it cross-reacts with an antibody for the α/β-subunit of the ATP synthase from beef heart mitochondria. The purified protein has been analyzed by MALDI-TOF mass spectrometry and the results, covering the 30% of assigned sequence, indicate that it corresponds to the β-subunit of the ATP synthase of pea mitochondria. It is suggested that this enzymatic protein may perform a dual function as soluble PPiase or as subunit of the more complex ATP synthase. [Copyright &y& Elsevier]

• Alpha and beta diversity distribution revealed hotspots within hotspots of endemism. • Geomorphology and climate manly drive endemic species richness and composition. • Endemic richness pattern is consistent with local glacial refugia scenarios. • Detecting endemic hotspots is crucial for nature conservation purposes. Identification of centers of endemism is a crucial issue to improve the understanding on overall biodiversity distribution and related conservation actions. Despite the well-known distribution of global endemic areas, less effort has been devoted in defining local hotspots and their ecological determinants. In this study, we analyzed the distribution and the spatial pattern of endemic diversity of vascular plant in the south-eastern Italian Alps, aiming at identifying the occurrence of local hotspots and focusing on the relationships occurring between alpha (i.e. species richness) and beta diversity (i.e. Local Contributors of Beta Diversity) along with their ecological and spatial drivers. We observed that both alpha and beta diversity metrics have a strong negative relationship, showing a clear spatial pattern. Among the environmental drivers, geomorphological and climatic variables were the most influent, pointing out the importance of landscape heterogeneity and local oceanic climate conditions to favor endemic richness. We also found that historical factors (i.e. Last Glacial Maximum) significantly affected the pattern of endemic diversity. Interestingly, most of the variables showed contrasting effects on alpha and beta diversity. Our study proposes an approach for the identification of local hotspots of endemic species, which take into account both the spatially structured nature of ecological data and their associated environmental drivers. Our findings might provide new insights in the ecological process driving current endemic plant patterns and become pivotal for nature conservationist both to identify areas of high conservation value and to suggest appropriate management schemes also beyond existing protected areas. [ABSTRACT FROM AUTHOR]

Embolism repair ability has been documented in numerous species. Although the actual mechanism driving this phenomenon is still debated, experimental findings suggest that non-structural carbohydrates (NSC) stored in wood parenchyma would provide the osmotic forces to drive the refilling of embolized conduits. We selected 12 broadleaved species differing in vulnerability to xylem embolism (P 50) and amount of wood parenchyma in order to check direct evidence about the possible link(s) between parenchyma cells abundance, NSC availability and species-specific capacity to reverse xylem embolism. Branches were dehydrated until ∼50% loss of hydraulic conductivity was recorded (PLC ∼50%). Hydraulic recovery (ΔPLC) and NSC content was, then, assessed after 1h of rehydration. Species showed a different ability to recover their hydraulic conductivity from PLC ∼50%. Removing the bark in the species showing hydraulic recovery inhibited the embolism reversal. Strong correlations between the ΔPLC and: a) the amount of parenchyma cells (mainly driven by the pith area), b) the consumption of soluble NSC have been recorded. Our results support the hypothesis that refilling of embolized vessels is mediated by the mobilization of soluble NSC and it is mainly recorded in species with a higher percentage of parenchyma cells that may be important in the hydraulic recovery mechanism as a source of carbohydrates and/or as a source of water. Image 1 • Different species showed different xylem embolism reversal ability after 1 h of rehydration. • Girdling treatment inhibited the xylem refilling. • Parenchyma cells' amount and consumption of NSC correlated to refilling ability. • Recorded results confirm the biological nature of the embolism refilling. [ABSTRACT FROM AUTHOR]

To investigate the role of natural humic substances on plant cell phosphate level and metabolism, tobacco BY-2 suspension cell cultures were grown in the presence of humic samples of different chemical composition: soil humic acid and its three size-fractions (I–III) separated by High Pressure Size Exclusion Chromatography. The humic samples were characterized by CPMAS-NMR spectroscopy and on-line pyrolysis–gas chromatography–mass spectrometry. Suspension cell cultures, after 7 days of incubation, were facing Pi starvation. The fraction III, the most hydrophilic and smallest in molecular size among humic samples, induced a partial relief from Pi starvation, increasing total cell phosphate amount, ATP and glucose-6-phosphate levels, as well as the activity of secreted acid phosphatases. Furthermore, fraction III induced a decrease of KCN-insensitive respiration, evaluated in both suspension cells and isolated mitochondria. The low amount of acidic groups in fraction III excluded that its observed effect in relieving cells from Pi deficiency may be attributed to a partial replacement of the chelating ability of secreted acids (mainly citric and malic acids) in releasing Pi from metal–phosphate complexes. The molecular characteristics of fraction III are conducive to a flexible conformational structure due to hydrophilic domains, which are still contoured by hydrophobic moieties such as alkyl and aromatic compounds. Such flexible molecular associations may induce an efficient release of Pi from organic sources (e.g. nucleic acids), released in the media by damaged or dead cells, exerting a sort of positive effect on either the production or activity of extracellular Pi hydrolytic enzymes. This work shows that only by combining advanced molecular characterization of natural humic molecules with their effect on plant cells, it is possible to formulate sound hypotheses for structure–activity relationships. [Copyright &y& Elsevier]

• Species-habitat networks were applied for the first time to plant communities. • The network approach elucidated plant community interactions through colonization. • Colonization potential and species richness responded to habitat type and maturity. • Alien communities responded differently if compared with native communities. • Backdune habitats with low maturity are key nodes for alien invasions. Sand shore ecosystems are extremely vulnerable to alien plant invasions. While most of the abiotic drivers of alien success have been identified, less is known on the role of biological processes driving the invasion. Studying the interactions between alien and native plant communities across different habitats and along the ecological succession (i.e. community maturity) can elucidate the dynamics of alien invasions in dune systems. In this study, we sampled alien and native plant communities in 100 patches across 10 natural coastal landscapes in NE Italy. The patches represented three main habitat types (foredune, backdune and salt marsh, which differ in terms of sea storm-related disturbance and soil salinity) distributed along a gradient of community maturity (i.e. number of years since the plant community was completely eroded by a sea storm). We analysed the effects of alien/native status, habitat type and maturity on species richness and colonization potential of plant species pools. Colonization potential was estimated by applying for the first time on plant data a species-habitat network approach, which allowed us to assess in detail the effect of each plant community on the others. In backdune habitats, alien plant species richness was negatively related with community maturity, which in turn had a positive effect on native species richness. Colonization potential was positively influenced by age for native communities and negatively for alien communities in salt marshes. Among habitat types, backdune patches were also particularly prone to alien invasions and very efficient donors of alien plants to other patches. Salt marshes were in general very resistant to invasion but potentially acting as secondary reservoirs for some backdune alien species. This study identified backdune habitats as key nodes for alien plant introduction and spread in coastal ecosystems, underlining the importance of maintaining mature undisturbed patches as a barrier to alien invasions. This information could prove pivotal in optimizing monitoring and management efforts of alien plant species in these ecosystems, as well as in conservation prioritization. [ABSTRACT FROM AUTHOR]