Starting from known properties of non-specific salt effects on the surface tension at an air–water interface, we propose the first general, detailed qualitative molecular mechanism for the origins of ion-specific (Hofmeister) effects on the surface potential difference at an air–water interface; this mechanism suggests a simple model for the behaviour of water at all interfaces (including water–solute interfaces), regardless of whether the non-aqueous component is neutral or charged, polar or non-polar Specifically, water near an isolated interface is conceptually divided into three layers, each layer being 1 water-molecule thick We propose that the solute determines the behaviour of the adjacent first interfacial water layer ( I 1 ); that the bulk solution determines the behaviour of the third interfacial water layer ( I 3 ), and that both I 1 and I 3 compete for hydrogen-bonding interactions with the intervening water layer ( I 2 ), which can be thought of as a transition layer The model requires that a polar kosmotrope (polar water-structure maker) interact with I 1 more strongly than would bulk water in its place; that a chaotrope (water-structure breaker) interact with I 1 somewhat less strongly than would bulk water in its place; and that a non-polar kosmotrope (non-polar water-structure maker) interact with I 1 much less strongly than would bulk water in its place We introduce two simple new postulates to describe the behaviour of I 1 water molecules in aqueous solution The first, the ‘relative competition’ postulate, states that an I 1 water molecule, in maximizing its free energy (—δG), will favour those of its highly directional polar (hydrogen-bonding) interactions with its immediate neighbours for which the maximum pairwise enthalpy of interaction (—δ H ) is greatest; that is, it will favour the strongest interactions We describe such behaviour as ‘compliant’, since an I 1 water molecule will continually adjust its position to maximize these strong interactions Its behaviour towards its remaining immediate neighbours, with whom it interacts relatively weakly (but still favourably), we describe as ‘recalcitrant’, since it will be unable to adjust its position to maximize simultaneously these interactions The second, the ‘charge transfer’ postulate, states that the strong polar kosmotrope–water interaction has at least a small amount of covalent character, resulting in significant transfer of charge from polar kosmotropes to water–especially of negative charge from Lewis bases (both neutral and anionic); and that the water-structuring effect of polar kosmotropes is caused not only by the tight binding (partial immobilization) of the immediately adjacent ( I 1 ) water molecules, but also by an attempt to distribute among several water molecules the charge transferred from the solute When extensive, cumulative charge transfer to solvent occurs, as with macromolecular polyphosphates, the solvation layer (the layer of solvent whose behaviour is determined by the solute) can become up to 5- or 6-water-molecules thick We then use the ‘relative competition’ postulate, which lends itself to simple diagramming, in conjunction with the ‘charge transfer’ postulate to provide a new, startlingly simple and direct qualitative explanation for the heat of dilution of neutral polar solutes and the temperature dependence of relative viscosity of neutral polar solutes in aqueous solution This explanation also requires the new and intriguing general conclusion that as the temperature of aqueous solutions is lowered towards o °C, solutes tend to acquire a non-uniform distribution in the solution, becoming increasingly likely to cluster 2 water molecules away from other solutes and surfaces (the driving force for this process being the conversion of transition layer water to bulk water) The implications of these conclusions for understanding the mechanism of action of general (gaseous) anaesthetics and other important interfacial phenomena are then addressed

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033583500005369

The Hofmeister effect and the behaviour of water at interfaces.

Cellular tensegrity: defining new rules of biological design that govern the cytoskeleton

In the spectrum of plant-microbe interactions disease is a rare outcome. In many interactions complex, integrated defense mechanisms prevent infection and disease. These defensive systems include preformed physical and chemical barriers as well as inducible defenses such as the strengthening of cell walls or synthesis of antimicrobial compounds (i.e., phytoalexins) and proteins.1,2 In certain cases plants react to pathogen attack by developing long-lasting, broad-spectrum systemic resistance to later attacks by pathogens. This phenomenon, termed systemic acquired resistance (SAR), has been observed in many species and may be ubiquitous among higher plants. In the last five years progress has been made toward understanding the molecular basis of SAR. In this review we first provide a brief history of SAR research, then describe our present knowledge of the manifestation and induction of SAR. We discuss recent findings that indicate a central role for the SAR pathway in plant health and finally present our current working model of SAR induction.

/pdf/systemic-acquired-resistance-2qr1m6rcwh.pdf

Systemic Acquired Resistance

Plant transformation is now a core research tool in plant biology and a practical tool for cultivar improvement. There are verified methods for stable introduction of novel genes into the nuclear genomes of over 120 diverse plant species. This review examines the criteria to verify plant transformation; the biological and practical requirements for transformation systems; the integration of tissue culture, gene transfer, selection, and transgene expression strategies to achieve transformation in recalcitrant species; and other constraints to plant transformation including regulatory environment, public perceptions, intellectual property, and economics. Because the costs of screening populations showing diverse genetic changes can far exceed the costs of transformation, it is important to distinguish absolute and useful transformation efficiencies. The major technical challenge facing plant transformation biology is the development of methods and constructs to produce a high proportion of plants showing predictable transgene expression without collateral genetic damage. This will require answers to a series of biological and technical questions, some of which are defined.

PLANT TRANSFORMATION: Problems and Strategies for Practical Application

Under appropriate in vivo or in vitro conditions, certain somatic plant cells have the capability to initiate embryogenic development (somatic embryogenesis). Somatic embryogenesis provides an unique experimental model to understand the molecular and cellular bases of developmental plasticity in plants. In the last few years, the application of modern experimental techniques, as well as the characterization of Arabidopsis embryogenesis mutants, have resulted in the accumulation of novel data about the acquisition of embryogenic capabilities by somatic plant cells. In this review, we summarize relevant experimental observations that can contribute to the description and definition of a transitional state of somatic cells induced to form totipotent, embryogenic cells. During this somatic-to-embryogenic transition, cells have to dedifferentiate, activate their cell division cycle and reorganize their physiology, metabolism and gene expression patterns. The roles of stress, endogenous growth regulators and chromatin remodelling in the coordinated reorganization of the cellular state are especially emphasized.

http://www.cas.miamioh.edu/~meicenrd/pdevlmnt/feheretal2003.pdf

Transition of somatic plant cells to an embryogenic state

Summary

Tungsten and gold particles, coated with plasmid DNA harboring the β-glucuronidase (GUS) and neomycin phosphotransferase II (npt-II) genes, were delivered into tobacco primary leaves and suspension-cultured cells of maize using the helium particle inflow gun. Cell viability and particle localization were determined 1 and 2 days after bombardment. Of the counted particles, 7–10% penetrated into or through the epidermis. Blue spots on tobacco leaves appeared as a blue area around a single, densely stained particle-containing central cell. DNA-coated gold particles provoked smaller spots with less diffusion and gave rise to more individual events than tungsten particles. In more than 90% of the GUS-positive epidermal and mesophyll cells, a particle was detectable within their nucleus. Two days after bombardment, viability had decreased to 1–2% in particle-containing cells.



Penetration of a cell by a particle was accompanied by callose formation in the wound area. Dead suspension culture cells of maize without callose formation but containing particles were detected just 1 h post-bombardment. Living cells with callose spots appeared more frequently after bombardment with tungsten than gold. As in tobacco, GUS expression was limited to those cells containing a particle in their nucleus, and the number of particle-containing, viable cells was low after 48 h.



The frequency of stable expression events was compared to the number of surviving tobacco leaf cells. On average, four kanamycin-resistant calli or plantlets were recovered per bombarded dish, of which approximately 50% were also GUS-positive. This corresponds to a stable-to-transient ratio of approximately 0.8%, and is similar to the number of particle-containing cells surviving after 48 h.

Early events in microprojectile bombardment: cell viability and particle location

A reliable protocol for the transformation of cultivated sunflower (Helianthus annuus L.) has been established, based on microprojectile bombardment of half shoot apices in combination with Agrobacterium tumefaciens coculture. Transgenic shoots have been obtained from 5 inbred lines, although transformation efficiencies varied with the genotype. Plants expressing the transgenes could be recovered from up to 7% of the explants. A minority of plants was shown to be chimaeric for expression of s-glucuronidase activity while most appeared to be uniformly transformed. Genetic segregation was 3∶1 for both s-glucuronidase and neomycine phospho transferase in some plants, indicating that the respective mother plants were uniformly transformed. Integration of the foreign genes was also shown by Southern analysis.

Transformation of sunflower (Helianthus annuus L.): a reliable protocol.

Agrobacterium -mediated transformation of shoot apices of sunflower (Helianthus annuus L.) was evaluated following wounding by cell-wall-digesting enzymes and sonication. The frequency of explants with regenerated shoots expressing GUS (beta-glucuronidase) or GFP (green fluorescent protein) increased following treatment with the macerating enzymes cellulase Onozuka R-10 and pectinase Boerozym M5, whereas treatment with macerozyme R-10 had a negative effect. When a combination of cellulase (0.1%) and pectinase (0.05%) was used, the rate of explants with uniformly GUS-positive shoots increased at least twofold. The transient expression of reporter genes was also enhanced using sonication (50 MHz; 2, 4 and 6 s), but stable expression in regenerated shoots following 4 weeks of selection did not increase with this treatment. Enzyme treatment alone (0.1% cellulase and 0.05% pectinase) was superior to a combined treatment of sonication and enzymes with respect to stable transformation. Polymerase chain reaction analyses of shoots recovered by grafting from transformation experiments using GFP as the reporter gene demonstrated the stable integration of the transgene. Regenerated plants were fertile and seeds could be harvested.

Improved Agrobacterium-mediated transformation of sunflower (Helianthus annuus L.): assessment of macerating enzymes and sonication.

Immature zygotic embryos of sunflower (Helianthus annuus L.) produce somatic embryos when cultured on medium supplemented with a cytokinin as the sole source of exogenous growth regulators. The timing of the induction phase and subsequent morphogenic events have been well characterized in previous work. We address here the question of the role of endogenous indole-3-acetic acid (IAA), since auxins are known to have a crucial role in the induction of somatic embryogenesis in many other culture and regeneration systems. The fact that in the sunflower system no exogenous auxin is required for the induction of somatic embryos makes this system very suitable for the study of the internal dynamics of IAA. We used an immuno-cytochemical approach to visualize IAA distribution within the explants before, during and after the induction phase. IAA accumulated transiently throughout cultured embryos during the induction phase. The detected signal was not uniform but certain tissues, such as the root cap and the root meristem, accumulated IAA in a more pronounced manner. IAA accumulation was not restricted to the reactive zone but the kinetics of endogenous variations strikingly mimic the pulse of IAA that is usually provoked by exogenous IAA application. The direct evidence presented here indicates that an endogenous auxin pulse is indeed among the first signals leading to the induction of somatic embryogenesis.

Günther Hahne

Papers

Early events in microprojectile bombardment: cell viability and particle location

Transformation of sunflower (Helianthus annuus L.): a reliable protocol.

Improved Agrobacterium-mediated transformation of sunflower (Helianthus annuus L.): assessment of macerating enzymes and sonication.

Immuno-cytochemical localization of indole-3-acetic acid during induction of somatic embryogenesis in cultured sunflower embryos

Plant regeneration at high frequency from mature sunflower cotyledons