Structural insights into light-driven anion pumping in cyanobacteria

Transmembrane ion transport is a key process in living cells. Active transport of ions is carried out by various ion transporters including microbial rhodopsins (MRs). MRs perform diverse functions such as active and passive ion transport, photo-sensing, and others. In particular, MRs can pump various monovalent ions like Na⁺, K⁺, Cl^-, I^-, NO₃^-. The only characterized MR proposed to pump sulfate in addition to halides belongs to the cyanobacterium Synechocystis sp. PCC 7509 and is named Synechocystis halorhodopsin (SyHR). The structural study of SyHR may help to understand what makes an MR pump divalent ions. Here we present the crystal structure of SyHR in the ground state, the structure of its sulfate-bound form as well as two photoreaction intermediates, the K and O states. These data reveal the molecular origin of the unique properties of the protein (exceptionally strong chloride binding and proposed pumping of divalent anions) and sheds light on the mechanism of anion release and uptake in cyanobacterial halorhodopsins. The unique properties of SyHR highlight its potential as an optogenetics tool and may help engineer different types of anion pumps with applications in optogenetics.

Abstract 2154: PARP7 inhibitor RBN-2397 increases tumoral IFN signaling leading to various tumor cell intrinsic effects and tumor regressions in mouse models

Targeting cytosolic nucleic acid sensing pathways to activate the Type I interferon (IFN) response is an emerging therapeutic strategy being explored in oncology. The PARP family consists of seventeen enzymes that regulate fundamental biological processes including response to cellular stress. PARP7 (TIPARP) is a stress-induced mono-ART that catalyzes the transfer of a single unit of ADP-ribose onto substrates (MARylation) to regulate their function and plays a role in suppressing the Type I IFN response in tumor cells (Gozgit 2021 Cancer Cell). RBN-2397 is the first potent and selective small molecule inhibitor of PARP7 catalytic function. To investigate the cell autonomous effects of PARP7 inhibition, we performed a cell line screen to identify PARP7 dependent cancer cell lines. We found that treatment of a subset of lines across several cancers led to a robust decrease in cell viability. Additionally, dosing of tumor bearing mice led to complete regressions in NCI-H1373 lung cancer xenografts. To investigate the mechanism of action (MOA) leading to decreased cell viability, we treated NCI-H1373 cells with RBN-2397 and found accumulation of cells in the G0/G1 phase of the cell cycle indicative of a cell cycle arrest. This arrest in NCI-H1373 cells was associated with the induction of senescence and increased mRNA expression of senescence associated secretory phenotype (SASP) genes. To evaluate the in vivo MOA, we performed an NCI-H1373 xenograft study and collected tumors after 7 days of RBN-2397 treatment. PARP7 inhibition led to decreased expression of Ki67, and increased expression of P21 and cleaved caspase-3, suggesting decreased proliferation and increased apoptosis. Increased expression of SASP genes was also observed in RBN-2397 treated tumors. Finally, we investigated transcriptional changes after RBN-2397 treatment by RNA sequencing. In addition to the effects observed in Type I IFN signaling, we also observed differential expression of genes associated with other pathways including autophagy and energy metabolism. Further evaluation of key autophagy proteins revealed that RBN-2397 affects autophagy flux and leads to a decrease in the oxygen consumption rate of cells and reduced ATP production from the mitochondria, suggesting that a change in energy metabolism may be related to the tumor intrinsic effect of RBN-2397. In summary, we show treatment of cancer cells with RBN-2397 not only leads to activation of tumor cell IFN signaling, but also causes G1 arrest and senescence, and changes in cancer cell autophagy and energy metabolism. In vivo, RBN-2397 treatment leads to complete tumor regressions in xenografts accompanied by decreased proliferation and increased apoptosis of tumor cells. RBN-2397 is currently being evaluated in the clinic as single agent in selected cancer types (NCT04053673) and in combination with anti-PD-1 therapies.

Citation Format: Jennifer R. Molina, Joseph M. Gozgit, Melissa M. Vasbinder, Ryan P. Abo, Kaiko kunii, Kristy G. Kuplast-Barr, Bin Gui, Sunaina P. Nayak, Elena Minissale, Kerren K. Swinger, Tim J. Wigle, Alvin Z. Lu, Danielle J. Blackwell, Christina R. Majer, Yue Ren, Ellen Bamberg, Mario Niepel, Jan-Rung Mo, William D. Church, Ahmed S. Mady, Jeff Song, Zacharenia A. Varsamis, Luke Utley, Patricia E. Rao, Timoty J. Mitchison, Kevin W. Kuntz, Victoria M. Richon, Kristen McEachern, Heike Keilhack. PARP7 inhibitor RBN-2397 increases tumoral IFN signaling leading to various tumor cell intrinsic effects and tumor regressions in mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2154.

PARP7 negatively regulates the type I interferon response in cancer cells and its inhibition triggers antitumor immunity

PARP7 is a monoPARP that catalyzes the transfer of single units of ADP-ribose onto substrates to change their function. Here, we identify PARP7 as a negative regulator of nucleic acid sensing in tumor cells. Inhibition of PARP7 restores type I interferon (IFN) signaling responses to nucleic acids in tumor models. Restored signaling can directly inhibit cell proliferation and activate the immune system, both of which contribute to tumor regression. Oral dosing of the PARP7 small-molecule inhibitor, RBN-2397, results in complete tumor regression in a lung cancer xenograft and induces tumor-specific adaptive immune memory in an immunocompetent mouse cancer model, dependent on inducing type I IFN signaling in tumor cells. PARP7 is a therapeutic target whose inhibition induces both cancer cell-autonomous and immune stimulatory effects via enhanced IFN signaling. These data support the targeting of a monoPARP in cancer and introduce a potent and selective PARP7 inhibitor to enter clinical development.

Abstract 1344: Small molecule inhibitor of CD38 modulates its intra- and extracellular functions leading to antitumor activity

CD38 is an ADP-ribosyl cyclase that converts NAD+ to ADP-ribose (ADPR) or cyclic ADPR (cADPR) and nicotinamide. The enzyme can exist in either an ecto- or endo-catalytic orientation with different sub-cellular localization, and therefore can regulate internal and external NAD+ pools. Both NAD+ and cADPR can impact T cell fitness and effector function, and CD38 has been shown to be increased in settings of chronic T cell activation. CD38 can mediate the non-canonical generation of the immune suppressive adenosine by catabolizing extracellular NAD+ resulting in immunosuppression in the microenvironment. Upon immune checkpoint inhibitor (ICI) therapy, CD38 is upregulated on cancer cells to drive ICI resistance. Therefore CD38, through its catalytic activity, has been implicated in tumor immune suppression and ICI resistance. Genetic knockout of CD38 has been shown to prevent tumor growth and improve T cell fitness. Here, we describe the effects of CD38 inhibition using a small molecule inhibitor on these key metabolites in various cellular and tumor models.

RBN013209 is a potent and selective small molecule inhibitor of CD38 catalytic function. We demonstrate that inhibition of CD38 with RBN013209 prevents conversion of extracellular NAD+ to ADPR or cADPR in cancer cell lines and PBMCs. Similarly, RBN013209 inhibited intracellular CD38 activity and elevated intracellular NAD+ levels in cultured human primary T cells. Oral administration of RBN013209 to naïve mice resulted in dose-dependent elevation of NAD+ and reduction of ADPR in various tissues such as spleen and liver. We next assessed the expression of CD38 protein by immunohistochemistry following ICI treatment in various syngeneic cancer models to select a model for efficacy studies. We observed increases in CD38 expression on tumor cells and infiltrating immune cells in MC38 colon cancer and B16-F10 and Cloudman S91 melanoma models. In the MC38 tumor model, we observed single agent antitumor activity with RBN013209 that was associated with changes in NAD+ and ADPR. In B16-F10 tumor-bearing mice, we observed antitumor activity with RBN013209 in combination with anti-PD-L1 therapy. To evaluate CD38 as a biomarker in clinical samples, we assessed and confirmed the tumor expression of CD38 protein from lung, prostate and kidney cancer patients.

Here, we show that inhibition of CD38 with a small molecule affects both intra- and extra-cellular CD38 activity and modulates key metabolites playing an important role in immunomodulation. Further, our data indicate that CD38 is increased by ICI treatment and that inhibition of CD38 can lead to antitumor activity.

Citation Format: Prashant Shambharkar, Danielle J. Blackwell, Melissa M. Vasbinder, Laurie B. Schenkel, Kaiko Kunii, Jenkins L. Lemera, Kristy G. Kuplast-Barr, Yue Ren, Ellen Bamberg, W. David Church, Christina R. Majer, Luke Utley, Kristen McEachern, Mario Niepel, Tim J. Wigle, Kevin W. Kuntz, Victoria M. Richon, Heike Keilhack, Joseph M. Gozgit. Small molecule inhibitor of CD38 modulates its intra- and extracellular functions leading to antitumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1344.

Abstract 3405: PARP7 negatively regulates the type I interferon response in cancer cells and its inhibition leads to tumor regression

Targeting cytosolic nucleic acid sensing pathways and the Type I interferon (IFN) response is an emerging therapeutic strategy being explored in oncology. PARP7 is a member of the monoPARP class of enzymes, which catalyze the transfer of single units of ADP-ribose onto substrates to change their function. PARP7 expression is increased by cellular stress and aromatic hydrocarbons, and the PARP7 gene is amplified in cancers, especially in those of the upper aerodigestive tract. PARP7 has also been reported to negatively regulate the Type I IFN response by interacting with TBK1 during viral infection. Herein, we identify PARP7 as a novel negative regulator of cytosolic nucleic acid sensing in tumor cells.

RBN-2397, is a potent and selective small molecule inhibitor of PARP7 catalytic function. We identified a subset of cancers exhibiting dependency on PARP7 for proliferation and found that cell lines with higher baseline expression of interferon stimulated genes were more sensitive. We further show that inhibition of PARP7 by RBN-2397 restores Type I IFN signaling as demonstrated by the induction of STAT1 phosphorylation and up-regulation of genes enriched for Type I IFN signaling in NCI-H1373 lung cancer cells. We examined the antitumor effects of once daily orally administered RBN-2397 in SCID mice with subcutaneous NCIH1373 xenograft tumors and observed a dose-dependent effect of RBN-2397 on tumor growth, with regressions at dose levels ≥30 mg/kg. To evaluate the antitumor immune response in vivo, we administered RBN-2397 to CT26 tumor-bearing, immunocompetent BALB/c mice, and observed significant tumor growth inhibition at all dose levels with complete and durable regressions in a subset of mice. All of these tumor-free mice rejected a challenge of injected CT26 cells, but were able to develop 4T1 tumors, demonstrating induction of tumor-specific adaptive immune memory. The antitumor effects of RBN-2397 were further enhanced when combined with an immune checkpoint inhibitor, anti-PD1. Using CRISPR-Cas9 to knockout either TBK1 or IFNAR1 in CT26 cells, we demonstrated that RBN-2397 antitumor immunity is dependent on the effects of tumor-derived Type I interferon on immune cells.

Here, we show for the first time that cancer cells use PARP7 to suppress the Type I IFN response to cytosolic nucleic acids. We have discovered and developed RBN-2397, a first-in-class, potent and selective inhibitor of PARP7. We show RBN-2397 restores Type I IFN signaling in the tumor, causes complete tumor regressions and adaptive immunity in murine models. RBN-2397 is the first agent to enter clinical trials that targets this tumor-intrinsic vulnerability.

Citation Format: Joseph M. Gozgit, Melissa M. Vasbinder, Ryan P. Abo, Kaiko Kunii, Kristy G. Kuplast-Barr, Bin Gui, Alvin Z. Lu, Kerren K. Swinger, Tim J. Wigle, Danielle J. Blackwell, Christina R. Majer, Yue Ren, Mario Niepel, Zacharenia A. Varsamis, Sunaina P. Nayak, Ellen Bamberg, Jan-Rung Mo, William Church, Jeff Song, Luke Utley, Patricia E. Rao, Timothy J. Mitchison, Kevin W. Kuntz, Victoria M. Richon, Heike Keilhack. PARP7 negatively regulates the type I interferon response in cancer cells and its inhibition leads to tumor regression [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3405.

Abstract DDT02-01: RBN-2397: A first-in-class PARP7 inhibitor targeting a newly discovered cancer vulnerability in stress-signaling pathways

RBN-2397: A first-in-class PARP7 inhibitor targeting a newly discovered cancer vulnerability in stress-signaling pathways PARP7 is a monoPARP that catalyzes the transfer of single units of ADP-ribose onto substrates to change their function (MARylation). PARP7 expression is increased by cellular stresses, including aromatic hydrocarbons and the PARP7 gene is amplified in cancers, especially in those of the upper aerodigestive tract. PARP7 has also been reported to negatively regulate the Type I interferon (IFN) response by interacting with TBK1 during viral infection. As part of our drug discovery efforts to identify inhibitors of PARP7, we utilized structure-based drug design to optimize an unselective monoPARP inhibitor identified by screening Ribon's internal compound collection of PARP inhibitors. Further optimization of potency and physicochemical properties led to the discovery of RBN-2397, a potent and selective small molecule inhibitor of PARP7 catalytic function. A co-crystal structure of RBN-2397 demonstrated binding of the compound in the NAD+-binding pocket. Binding to cellular PARP7 is demonstrated by the ability of RBN-2397 to displace an active site probe in a NanoBRET assay. Functionally, RBN-2397 leads to the inhibition of MARylation of multiple intracellular proteins in PARP7-overexpressing SK-MES-1 cells. We identified a subset of cancers exhibiting dependency on PARP7 for proliferation. Cell lines with higher baseline expression of interferon stimulated genes are more sensitive to RBN-2397 in proliferation assays. We further show that inhibition of PARP7 by RBN-2397 restores Type I IFN signaling as demonstrated by the induction of STAT1 phosphorylation and upregulation of genes enriched for Type I IFN signaling in NCI-H1373 lung cancer cells. Oral dosing of RBN-2397 results in durable, complete tumor regression in a NCI-H1373 lung cancer xenograft and induces tumor-specific adaptive immune memory in an immunocompetent mouse cancer model that is dependent on tumor-derived Type I IFN signaling. Herein, we describe the discovery of the small molecule PARP7 inhibitor RBN-2397, the first therapeutic agent targeting PARP7 to enter clinical trials, and the first disclosure of the inhibitor. We demonstrate PARP7 is a novel therapeutic target and inhibition of PARP7 by RBN-2397 induces both cancer cell autonomous and immune stimulatory effects via enhanced IFN signaling.

Citation Format: Melissa M. Vasbinder, Joseph M. Gozgit, Ryan P. Abo, Kaiko Kunii, Kristy G. Kuplast-Barr, Bin Gui, Alvin Z. Lu, Kerren K. Swinger, Tim J. Wigle, Danielle J. Blackwell, Christina R. Majer, Yue Ren, Mario Niepel, Zacharenia A. Varsamis, Sunaina P. Nayak, Ellen Bamberg, Jan-Rung Mo, W David Church, Jeff Song, Luke Utley, Patricia E. Rao, Timothy J. Mitchison, Kevin W. Kuntz, Victoria M. Richon, Heike Keilhack. RBN-2397: A first-in-class PARP7 inhibitor targeting a newly discovered cancer vulnerability in stress-signaling pathways [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr DDT02-01.

High-resolution structural insights into the heliorhodopsin family

Rhodopsins are the most abundant light-harvesting proteins. A new family of rhodopsins, heliorhodopsins (HeRs), has recently been discovered. Unlike in the known rhodopsins, in HeRs the N termini face the cytoplasm. The function of HeRs remains unknown. We present the structures of the bacterial HeR-48C12 in two states at the resolution of 1.5 Å, which highlight its remarkable difference from all known rhodopsins. The interior of HeR's extracellular part is completely hydrophobic, while the cytoplasmic part comprises a cavity (Schiff base cavity [SBC]) surrounded by charged amino acids and containing a cluster of water molecules, presumably being a primary proton acceptor from the Schiff base. At acidic pH, a planar triangular molecule (acetate) is present in the SBC. Structure-based bioinformatic analysis identified 10 subfamilies of HeRs, suggesting their diverse biological functions. The structures and available data suggest an enzymatic activity of HeR-48C12 subfamily and their possible involvement in fundamental redox biological processes.

Temperature jump study of charge translocation during the bacteriorhodopsin photocycle

Temperature jump experiments were carried out on purple membranes oriented and fixed in polyacrylamide gel. With green background illumination a relaxation of the photocurrent after an infrared laser pulse could be observed. To simulate the temperature jump signals different models of the bacteriorhodopsin photocycle were tested. The parameters of these models were obtained by measuring absorbance changes and photocurrent after excitation with a 575-nm laser flash.A model with a temperature-dependent branching before the M state turned out to be satisfying. Other models, especially those with a late branching or without branching, could not reproduce the temperature jump measurements.

Effects of environmental parameters and irrigation on the turgor pressure of banana plants measured using the non-invasive, online monitoring leaf patch clamp pressure probe

Turgor pressure provides a sensitive indicator for irrigation scheduling. Leaf turgor pressure of Musa acuminate was measured by using the so-called leaf patch clamp pressure probe, i.e. by application of an external, magnetically generated and constantly retained clamp pressure to a leaf patch and determination of the attenuated output pressure P(p) that is highly correlated with the turgor pressure. Real-time recording of P(p) values was made using wireless telemetric transmitters, which send the data to a receiver base station where data are logged and transferred to a GPRS modem linked to an Internet server. Probes functioned over several months under field and laboratory conditions without damage to the leaf patch. Measurements showed that the magnetic-based probe could monitor very sensitively changes in turgor pressure induced by changes in microclimate (temperature, relative humidity, irradiation and wind) and irrigation. Irrigation effects could clearly be distinguished from environmental effects. Interestingly, oscillations in stomatal aperture, which occurred frequently below turgor pressures of 100 kPa towards noon at high transpiration or at high wind speed, were reflected in the P(p) values. The period of pressure oscillations was comparable with the period of oscillations in transpiration and photosynthesis. Multiple probe readings on individual leaves and/or on several leaves over the entire height of the plants further emphasised the great impact of this non-invasive turgor pressure sensor system for elucidating the dynamics of short- and long-distance water transport in higher plants.

A non-invasive probe for online-monitoring of turgor pressure changes under field conditions

An advanced non-invasive, field-suitable and inexpensive leaf patch clamp pressure probe for online-monitoring of the water relations of intact leaves is described. The probe measures the attenuated output patch clamp pressure, P(p), of a clamped leaf in response to an externally applied input pressure, P(clamp). P(clamp) is generated magnetically. P(p) is sensed by a pressure sensor integrated into the magnetic clamp. The magnitude of P(p) depends on the transfer function, T(f), of the leaf cells. T(f) consists of a turgor pressure-independent (related to the compression of the cuticle, cell walls and other structural elements) and a turgor pressure-dependent term. T(f) is dimensionless and assumes values between 0 and 1. Theory shows that T(f) is a power function of cell turgor pressure P(c). Concomitant P(p) and P(c) measurements on grapevines confirmed the relationship between T(f) and P(c). P(p) peaked if P(c) approached zero and assumed low values if P(c) reached maximum values. The novel probe was successfully tested on leaves of irrigated and non-irrigated grapevines under field conditions. Data show that slight changes in the microclimate and/or water supply (by irrigation or rain) are reflected very sensitively in P(p).

Evidence for discontinuous water columns in the xylem conduit of tall birch trees

The continuity of the xylem water columns was studied on 17- to 23-m tall birch trees (trunk diameter about 23 cm; first branching above 10 m) all year round. Fifty-one trees were felled, and 5-cm thick slices or 2-m long boles were taken at regular, relatively short intervals over the entire height of the trees. The filling status of the vessels was determined by (i) xylem sap extraction from trunk and branch pieces (using the gas bubble-based jet-discharge method and centrifugation) and from trunk boles (using gravity discharge); (ii) (1)H nuclear magnetic resonance imaging of slice pieces; (iii) infusion experiments (dye, (86)Rb(+), D(2)O) on intact trees and cut branches; and (iv) xylem pressure measurements. This broad array of techniques disclosed no evidence for continuous water-filled columns, as postulated by the Cohesion-Tension theory, for root to apex directed mass transport. Except in early spring (during the xylem refilling phase) and after extremely heavy rainfall during the vegetation period, cohesive/mobile water was found predominantly at intermediate heights of the trunks but not at the base or towards the top of the tree. Similar results were obtained for branches. Furthermore, upper branches generally contained more cohesive/mobile water than lower branches. The results suggest that water lifting occurs by short-distance (capillary, osmotic and/or transpiration-bound) tension gradients as well as by mobilisation of water in the parenchymatic tissues and the heartwood, and by moisture uptake through lenticels.

The mechanisms of refilling of xylem conduits and bleeding of tall birch during spring

Seasonal variations in osmolality and components of xylem sap in tall birch trees were determined using several techniques. Xylem sap was extracted from branch and trunk sections of 58 trees using the very rapid gas bubble-based jet-discharge method. The 5-cm long wood pieces were taken at short intervals over the entire tree height. The data show that large biphasic osmolality gradients temporarily exist within the conducting xylem conduits during leaf emergence (up to 272 mosmol x kg(-1) at the apex). These gradients (arising mainly from glucose and fructose) were clearly held within the xylem conduit as demonstrated by (1)H NMR imaging of intact twigs. Refilling experiments with benzene, sucrose infusion, electron and light microscopy, as well as (1)H NMR chemical shift microimaging provided evidence that the xylem of birch represents a compartment confined by solute-reflecting barriers (radial: lipid linings/lipid bodies; axial: presumably air-filled spaces). These features allow transformation of osmolality gradients into osmotic pressure gradients. Refilling of the xylem occurs by a dual mechanism: from the base (by root pressure) and from the top (by hydrostatic pressure generated by xylem-bound osmotic pressure). The generation of osmotic pressure gradients was accompanied by bleeding. Bleeding could be observed at a height of up to 21 m. Bleeding rates measured at a given height decreased exponentially with time. Evidence is presented that the driving force for bleeding is the weight of the static water columns above the bleeding point. The pressure exerted by the water columns and the bleeding volume depend on the water-filling status of (communicating) vessels.

Effects on capacitance by overexpression of membrane proteins

Functional Channelrhodopsin-2 (ChR2) overexpression of about 10(4)channels/mum(2) in the plasma membrane of HEK293 cells was studied by patch-clamp and freeze-fracture electron microscopy. Simultaneous electrorotation measurements revealed that ChR2 expression was accompanied by a marked increase of the area-specific membrane capacitance (C(m)). The C(m) increase apparently resulted partly from an enlargement of the size and/or number of microvilli. This is suggested by a relatively large C(m) of 1.15+/-0.08 microF/cm(2) in ChR2-expressing cells measured under isotonic conditions. This value was much higher than that of the control HEK293 cells (0.79+/-0.02 microF/cm(2)). However, even after complete loss of microvilli under strong hypoosmolar conditions (100 mOsm), the ChR2-expressing cells still exhibited a significantly larger C(m) (0.85+/-0.07 microF/cm(2)) as compared to non-expressing control cells (0.70+/-0.03 microF/cm(2)). Therefore, a second mechanism of capacitance increase may involve changes in the membrane permittivity and/or thickness due to the embedded ChR2 proteins.

A combined patch-clamp and electrorotation study of the voltage- and frequency-dependent membrane capacitance caused by structurally dissimilar lipophilic anions

Interactions of structurally dissimilar anionic compounds with the plasma membrane of HEK293 cells were analyzed by patch clamp and electrorotation. The combined approach provides complementary information on the lipophilicity, preferential affinity of the anions to the inner/outer membrane leaflet, adsorption depth and transmembrane mobility. The anionic species studied here included the well-known lipophilic anions dipicrylamine (DPA⁻), tetraphenylborate (TPB⁻) and [W₂(CO)₁₀(S₂CH)]⁻, the putative lipophilic anion \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\text{B}}{\left( {{\text{CF}}_{3} } \right)}^{ - }_{4} $$\end{document} and three new heterocyclic W(CO)₅ derivatives. All tested anions partitioned strongly into the cell membrane, as indicated by the capacitance increase in patch-clamped cells. The capacitance increment exhibited a bell-shaped dependence on membrane voltage. The midpoint potentials of the maximum capacitance increment were negative, indicating the exclusion of lipophilic anions from the outer membrane leaflet. The adsorption depth of the large organic anions DPA⁻, TPB⁻ and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\text{B}}{\left( {{\text{CF}}_{3} } \right)}^{ - }_{4} $$\end{document} increased and that of W(CO)₅ derivatives decreased with increasing concentration of mobile charges. In agreement with the patch-clamp data, electrorotation of cells treated with DPA⁻ and W(CO)₅ derivatives revealed a large dispersion of membrane capacitance in the kilohertz to megahertz range due to the translocation of mobile charges. In contrast, in the presence of TPB⁻ and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\text{B}}{\left( {{\text{CF}}_{3} } \right)}^{ - }_{4} $$\end{document} no mobile charges could be detected by electrorotation, despite their strong membrane adsorption. Our data suggest that the presence of oxygen atoms in the outer molecular shell is an important factor for the fast translocation ability of lipophilic anions.

Foliar water supply of tall trees: evidence for mucilage-facilitated moisture uptake from the atmosphere and the impact on pressure bomb measurements

The water supply to leaves of 25 to 60 m tall trees (including high-salinity-tolerant ones) was studied. The filling status of the xylem vessels was determined by xylem sap extraction (using jet-discharge, gravity-discharge, and centrifugation) and by (1)H nuclear magnetic resonance imaging of wood pieces. Simultaneously, pressure bomb experiments were performed along the entire trunk of the trees up to a height of 57 m. Clear-cut evidence was found that the balancing pressure (P(b)) values of leafy twigs were dictated by the ambient relative humidity rather than by height. Refilling of xylem vessels of apical leaves (branches) obviously mainly occurred via moisture uptake from the atmosphere. These findings could be traced back to the hydration and rehydration of mucilage layers on the leaf surfaces and/or of epistomatal mucilage plugs. Xylem vessels also contained mucilage. Mucilage formation was apparently enforced by water stress. The observed mucilage-based foliar water uptake and humidity dependency of the P(b) values are at variance with the cohesion-tension theory and with the hypothesis that P(b) measurements yield information about the relationships between xylem pressure gradients and height.

A novel, non-invasive, online-monitoring, versatile and easy plant-based probe for measuring leaf water status

A high-precision pressure probe is described which allows non-invasive online-monitoring of the water relations of intact leaves. Real-time recording of the leaf water status occurred by data transfer to an Internet server. The leaf patch clamp pressure probe measures the attenuated pressure, P(p), of a leaf patch in response to a constant clamp pressure, P(clamp). P(p) is sensed by a miniaturized silicone pressure sensor integrated into the device. The magnitude of P(p) is dictated by the transfer function of the leaf, T(f), which is a function of leaf patch volume and ultimately of cell turgor pressure, P(c), as shown theoretically. The power function T(f)=f(P(c)) theoretically derived was experimentally confirmed by concomitant P(p) and P(c) measurements on intact leaflets of the liana Tetrastigma voinierianum under greenhouse conditions. Simultaneous P(p) recordings on leaflets up to 10 m height above ground demonstrated that changes in T(f) induced by P(c) changes due to changes of microclimate and/or of the irrigation regime were sensitively reflected in corresponding changes of P(p). Analysis of the data show that transpirational water loss during the morning hours was associated with a transient rise in turgor pressure gradients within the leaflets. Subsequent recovery of turgescence during the afternoon was much faster than the preceding transpiration-induced water loss if the plants were well irrigated. Our data show the enormous potential of the leaf patch clamp pressure probe for leaf water studies including unravelling of the hydraulic communication between neighbouring leaves and over long distances within tall plants (trees).