植物水孔蛋白介导的水分运输及其分析测定技术

水孔蛋白介导的水分运输具有选择性强、效率高和调节快等特点,在植物生长、发育和胁迫适应中起作用,文章介绍了水孔蛋白介导的水分运输及其分析测定技术.     

Focus on Water: Monitoring Plant Drought Stress Response Using Terahertz Time-Domain Spectroscopy

We present a novel measurement setup for monitoring changes in leaf water status using nondestructive terahertz time-domain spectroscopy (THz-TDS). Previous studies on a variety of plants showed the principal applicability of THz-TDS. In such setups, decreasing leaf water content directly correlates with increasing THz transmission. Our new system allows for continuous, nondestructive monitoring of the water status of multiple individual plants each at the same constant leaf position. It overcomes previous drawbacks, which were mainly due to the necessity of relocating the plants. Using needles of silver fir (Abies alba) seedlings as test subjects, we show that the transmission varies along the main axis of a single needle due to a variation in thickness. Therefore, the relocation of plants during the measuring period, which was necessary in the previous THz-TDS setups, should be avoided. Furthermore, we show a highly significant correlation between gravimetric water content and respective THz transmission. By monitoring the relative change in transmission, we were able to narrow down the permanent wilting point of the seedlings. Thus, we established groups of plants with well-defined levels of water stress that could not be detected visually. This opens up the possibility for a broad range of genetic and physiological experiments.Climate change simulations predict an increase in the occurrence of drought events in the Mediterranean area and in central Europe due to smaller amounts of precipitation, especially during summer periods (IPCC, 2007). With the exception of the boreal zone, this leads to an increase in drought risks for every region on the European continent (Iglesias et al., 2007). Water availability is very important for a variety of plant species. Trees and crops play major roles regarding ecosystem stability and food supply. Forest trees are keystone elements in shaping long-term, regional ecosystem composition and stability and are, like most forest species, highly vulnerable to increases in drought severity (Breshears et al., 2005; Choat et al., 2012). Drought-induced forest die-offs thereby directly reduce ecosystem services such as carbon sequestration and timber supply (Allen et al., 2010). Further research is clearly necessary to elucidate the physiological traits and responses of plants regarding their water status.European silver fir (Abies alba) is an important forest tree species of ecological and economic relevance. This study is embedded in the European project LinkTree, “linking genetic variability with ecological responses to environmental changes: forest trees as model systems.” Our group is concerned with the identification of genes involved in the water stress response of silver fir. This species is of special interest because of its lower water-use efficiency compared with other conifer species (Guehl and Aussenac, 1987; Guehl et al., 1991).For this purpose, monitoring plant water status without inducing other forms of stress is instrumental in order to apply well-defined levels of water stress. Obtaining information regarding the water status of a plant is highly problematic without using invasive and destructive methods that usually only allow a retrospective assessment. These include commonly established methods, such as the gravimetric water content and pressure chamber techniques, most notably Scholander’s pressure bomb (Scholander et al., 1965).Chlorophyll fluorescence, stomatal conductance, and visual assessment are examples of nondestructive and noninvasive measurement techniques. The former two only provide indirect information about the plant stress status and, therefore, the water content via photosynthetic activity (Lichtenthaler and Rinderle, 1988; Tardieu and Davies, 1993). The latter is difficult to standardize and highly dependent on the morphology of the studied plant species. Conifers especially are challenging subjects for visually assessing drought stress. Due to their needle morphology, it is nearly impossible to detect early signs of dehydration.Measurement techniques using electromagnetic radiation in the terahertz (THz) regime have shown promising results, due to the nondestructive nature and high sensitivity of THz waves to water. With THz waves, we refer to frequencies in the electromagnetic spectrum between 0.1 and 1 THz, corresponding to wavelengths between 3 and 0.3 mm, which are located between infrared light (thermal radiation) and microwave radiation (used in common wireless data communication systems). In the last decade, terahertz time-domain spectroscopy (THz-TDS) has proven to be a very strong and accurate tool for characterizing and imaging various materials (for review, see Jepsen et al., 2011). Crucial for our study is the remarkably high absorption coefficient of water in this part of the electromagnetic spectrum. Thus, it is a robust technique hardly affected by physiological concentrations of soluble substances. Using transmission geometry, the resulting absorption by plant tissues directly reflects the quantity of water molecules.Furthermore, THz-TDS does not suffer from the disadvantages of other radiation-based techniques. These are mainly focused on the infrared or microwave spectrum but either lack the sensitivity for small changes in leaf water status or are affected by the plant’s inorganic salt content, leading to significant disturbances (Ulaby and Jedlicka, 1984). Moreover, the applicability of emitting microwave radiation is limited to minimal wavelengths of approximately 2.5 mm. The Abbe diffraction limit, therefore, restricts the minimum diameter of a measurable object to approximately 1.25 mm. In order to measure small leaves, such as coniferous needles, electromagnetic radiation with shorter wavelengths is necessary.Although presenting a useful alternative, THz-TDS was not feasible until recently, due to the difficulty of generating and detecting electromagnetic radiation with wavelengths in the THz spectrum. Despite its promising applicability in plant sciences, until now this relatively novel method relied exclusively on measurement setups that allowed only a single measurement per alternating plant (Hadjiloucas et al., 1999; Jördens et al., 2009; Breitenstein et al., 2012; Castro-Camus et al., 2013; Gente et al., 2013). For the purpose of continuously monitoring multiple plants, these setups are only of limited use, since the plants must be relocated for every measurement. This results in two problems: (1) an increase in possible disturbances (e.g. mechanical), influencing the plant’s stress response, and (2) the necessity to precisely target the same measurement spot on every analyzed plant at every consecutive measurement. The latter is of crucial importance for the exact monitoring of any individual plant’s water status because, as we will show in this study, the transmission varies substantially across the area of plant leaf tissue.We present a novel measurement procedure that overcomes the drawbacks of previously proposed methods. Our approach enables us to precisely monitor changes in the water content of multiple plants simultaneously.In the course of this study, three different experiments were performed. The profile measurement and the rehydration experiment were preliminary investigations to examine the influences of needle and tissue thickness and to define a nonlethal stress level. The main experiment established groups of plants with comparable levels of water stress.     

植物水通道的生理生态特性及其参与气孔运动的研究进展

植物水通道对水分运输具有专一性,能够调节细胞中水分、一些离子和其他小溶质的转运,因而在植物的生长发育中发挥着重要作用.本文综述了植物水通道的研究进展,重点介绍了植物水通道的分子特性和生理生态特性及其在植物气孔运动中的作用,讨论了水通道在气孔振荡中的作用和地位.     

Water Relations of White Clover (Trifolium repens): Water Potential Gradients and Plant Morphology

Water potential, osmotic potential, pressure potential and relativewater content were measured in stolons and leaves of white cloverplants grown under a range of conditions of water supply andevaporative demand. The importance of adventitious roots fromthe nodes was examined. Gradients along stolons were alwaysextremely small, of the order of only 01 MPa. Stolon up waterpotential was representative of plant water status regardlessof stolon length, presence/absence of nodal roots, degree ofwater stress and evaporative demand. It is concluded that waterconduction along stolons was very good. Gradients were foundto exist along petioles; they may have a greater resistanceto water flow than stolons. The relationship between water fluxand stem anatomy, and the importance of differential flow ratesthrough stolons and petioles to plant behaviour during waterstress, are discussed. Trifolium repens L., white clover, water relations     

Sclerophylly and Plant Water Relations in Three Mediterranean Quercus Species

The possible role in drought resistance played by sclerophyllywas studied in the Mediterranean oaks Quercus ilex, Q. suberand Q. pubescens. Studies were conducted on leaves at 30, 50and 80% of their final surface area, as well as on mature leavesof the current year's growth in June and September and on 1-year-oldleaves. Leaves of different ages of the three species showed quite differentdegrees of sclerophylly (DS). Q. ilex leaves reached the definitiveDS of 1.75 g dm^–2 during leaf expansion; Q. pubescensleaves hardened at the end of their expansion, with a finalDS of 0.93 g dm^–2; Q. suber showed the lowest DS of 0.76g dm^–2. Leaf conductance to water vapour (g₁) of 1-year-old leaves ofQ. ilex, measured in the field, showed a duration of the g₁peak values about twice that of the other two species. The minimumleaf relative water content (RWC), however, was near the samein the three species, indicating that water loss was recoveredpartly by Q. ilex leaves. This was apparently due to the higherbulk modulus of elasticity (     

Therapeutic Effect of Agmatine on Neurological Disease: Focus on Ion Channels and Receptors

The central nervous system (CNS) is the most injury-prone part of the mammalian body. Any acute or chronic, central or peripheral neurological disorder is related to abnormal biochemical and electrical signals in the brain cells. As a result, ion channels and receptors that are abundant in the nervous system and control the electrical and biochemical environment of the CNS play a vital role in neurological disease. The N-methyl-d-aspartate receptor, 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl) propanoic acid receptor, kainate receptor, acetylcholine receptor, serotonin receptor, α2-adrenoreceptor, and acid-sensing ion channels are among the major channels and receptors known to be key components of pathophysiological events in the CNS. The primary amine agmatine, a neuromodulator synthesized in the brain by decarboxylation of l-arginine, can regulate ion channel cascades and receptors that are related to the major CNS disorders. In our previous studies, we established that agmatine was related to the regulation of cell differentiation, nitric oxide synthesis, and murine brain endothelial cell migration, relief of chronic pain, cerebral edema, and apoptotic cell death in experimental CNS disorders. In this review, we will focus on the pathophysiological aspects of the neurological disorders regulated by these ion channels and receptors, and their interaction with agmatine in CNS injury.

     

Photosynthetic CO2 Uptake and Whole Plant Growth as Related to Plant Water Relations

Morphological features of arid region plant life forms are described and interpreted as adaptations to drought although this cannot be easily quantified. Functional adaptations, however, can be measured, and using the annual crop plant Vigna unguiculata (L.) Walp. responses to drought are described at the leaf and the whole plant level. In the first step of this analysis theoretical criteria are developed to define optimal water use. In the second step experimental data are used to test to what extent Vigna follows a theoretically optimal regulation of water and carbon relations. The analysis indicates that the ecological adaptation of regulatory processes may be quantified at a functional level.     

Focus on Metabolism: Posttranslational Protein Modifications in Plant Metabolism

Posttranslational modifications (PTMs) of proteins greatly expand proteome diversity, increase functionality, and allow for rapid responses, all at relatively low costs for the cell. PTMs play key roles in plants through their impact on signaling, gene expression, protein stability and interactions, and enzyme kinetics. Following a brief discussion of the experimental and bioinformatics challenges of PTM identification, localization, and quantification (occupancy), a concise overview is provided of the major PTMs and their (potential) functional consequences in plants, with emphasis on plant metabolism. Classic examples that illustrate the regulation of plant metabolic enzymes and pathways by PTMs and their cross talk are summarized. Recent large-scale proteomics studies mapped many PTMs to a wide range of metabolic functions. Unraveling of the PTM code, i.e. a predictive understanding of the (combinatorial) consequences of PTMs, is needed to convert this growing wealth of data into an understanding of plant metabolic regulation.The primary amino acid sequence of proteins is defined by the translated mRNA, often followed by N- or C-terminal cleavages for preprocessing, maturation, and/or activation. Proteins can undergo further reversible or irreversible posttranslational modifications (PTMs) of specific amino acid residues. Proteins are directly responsible for the production of plant metabolites because they act as enzymes or as regulators of enzymes. Ultimately, most proteins in a plant cell can affect plant metabolism (e.g. through effects on plant gene expression, cell fate and development, structural support, transport, etc.). Many metabolic enzymes and their regulators undergo a variety of PTMs, possibly resulting in changes in oligomeric state, stabilization/degradation, and (de)activation (Huber and Hardin, 2004), and PTMs can facilitate the optimization of metabolic flux. However, the direct in vivo consequence of a PTM on a metabolic enzyme or pathway is frequently not very clear, in part because it requires measurements of input and output of the reactions, including flux through the enzyme or pathway. This Update will start out with a short overview on the major PTMs observed for each amino acid residue (PTMs, including determination of the localization within proteins (i.e. the specific residues) and occupancy. Challenges in dealing with multiple PTMs per protein and cross talk between PTMs will be briefly outlined. We then describe the major physiological PTMs observed in plants as well as PTMs that are nonenzymatically induced during sample preparation (PTMs, in particular for enzymes in primary metabolism (Calvin cycle, glycolysis, and respiration) and the C4 shuttle accommodating photosynthesis in C4 plants (PTMs observed in plants

压力探针技术在植物水分关系研究中的运用

压力探针（pressure probe）技术最初设计时用于测定巨型藻类细胞的膨压,后来转到对高等植物细胞的膨压及其他水分关系参数的测定,现在已发展成为植物生理学和生态学研究中的一种多用途技术。它可以在细胞原位测定水分及溶质跨膜运输及分布情况。能够在不离体的植物中测定水通道的活性。新近发展的木质部压力探针是惟一可以直接测定导管或管胞中负压的技术。文章介绍该技术基本原理及其在植物水分生理学研究中的应用。     

Focus on Ethylene: Bacterial Modulation of Plant Ethylene Levels

A focus on the mechanisms by which ACC deaminase-containing bacteria facilitate plant growth.Bacteria that produce the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, when present either on the surface of plant roots (rhizospheric) or within plant tissues (endophytic), play an active role in modulating ethylene levels in plants. This enzyme activity facilitates plant growth especially in the presence of various environmental stresses. Thus, plant growth-promoting bacteria that express ACC deaminase activity protect plants from growth inhibition by flooding and anoxia, drought, high salt, the presence of fungal and bacterial pathogens, nematodes, and the presence of metals and organic contaminants. Bacteria that express ACC deaminase activity also decrease the rate of flower wilting, promote the rooting of cuttings, and facilitate the nodulation of legumes. Here, the mechanisms behind bacterial ACC deaminase facilitation of plant growth and development are discussed, and numerous examples of the use of bacteria with this activity are summarized.Agricultural development policies and practices in the past sixty years have largely been based on external inputs (pesticides and fertilizers) to control soil-borne diseases and increase crop yields. Recently, stimulated by the awareness of potentially serious environmental and human health damage caused by the over use of agricultural chemicals (Alavanja et al., 2004; Leach and Mumford, 2008; Damalas and Eleftherohorinos, 2011), the controversy regarding the use of pesticides and fertilizers has gained prominence. Therefore, worldwide agricultural practice is moving toward a more sustainable and environmentally friendly approach.In 2002, in the European Union, 5.7 million ha were designated as being cultivated organically, and by 2011, this number had increased to 9.6 million ha (http://ec.europa.eu/agriculture/markets-and-prices/more-reports/pdf/organic-2013_en.pdf). In other words, in 10 years, the area devoted to organic agriculture in the European Union increased by approximately 400,000 ha per year. This growth in organic agriculture notwithstanding, the total amount of organically cultivated land represents only 5.4% of the total agricultural land in Europe. In this context, the use of microbial inoculants instead of traditional chemicals is gaining popularity, and a number of new products have been formulated, marketed, and applied successfully.The soil surrounding plant roots (the rhizosphere) is one of the main sources of bacteria expressing plant-beneficial activities ( i.e. plant growth-promoting bacteria [PGPB]; Bashan and Holguin, 1998). Stimulation of growth and protection of different crops from pathogens and abiotic stressors by PGPB is well documented under both controlled conditions and in the field, and a large number of papers on this topic are available (Reed and Glick, 2005, 2013; Thakore, 2006). The positive effects induced by PGPB on plant growth are based on: (1) the improvement of mineral nutrition (nitrogen fixation, phosphate solubilization, and iron sequestration), (2) the enhancement of plant tolerance to biotic and abiotic stress (largely mediated by 1-aminocyclopropane-1-carboxylate [ACC] deaminase), (3) the modification of root development (via phytohormone synthesis), and (4) the suppression of phytopathogens (by antibiotics, competition, lytic enzymes, systemic resistance, etc.; Fig. 1). The current knowledge of microorganisms living in the rhizosphere, their role, and their biotechnological and environmental applications has been summarized in several reviews (Glick, 2012; Hirsch and Mauchline, 2012; Bakker et al., 2013; Mendes et al., 2013; Reed and Glick, 2013). This review focuses on the role of bacterial ACC deaminase in supporting the growth of plants exposed to environmental stress. In addition, the issues of the distribution and phylogeny of ACC deaminase, and the possible role of ACC as a signaling molecule, are addressed.Open in a separate windowFigure 1.Schematic overview of the main mechanisms used by PGPB. Following the release of root exudates, a variety of soil microorganisms are attracted to the root. Some of them can efficiently colonize the root surface while others (endophytes) can penetrate the root tissue and spread inside the plant. Plant growth promotion by beneficial microorganisms may occur by either direct or indirect mechanisms. Direct promotion of plant growth involves the improvement of mineral nutrition via nitrogen fixation, phosphate solubilization, and iron chelation, as well as the modulation of phytohormones levels (auxins, cytokinins, GAs, and ethylene). In addition to the increase of biomass, PGPB can positively affect the nutritional value of fruits and edible seeds. The indirect mechanisms are based on the improvement of plant health via suppression of soil-borne diseases by antibiotics, lytic enzymes, siderophore production, induced systemic resistance involving jasmonate and ethylene signaling within the plant, and other molecules (the O-antigenic side chain of the bacterial outer membrane protein lipopolysaccharide, flagellar fractions, pyoverdine, 2,4-diacetylphloroglucinol, cyclic lipopeptide, surfactants, and salicylic acid) that stimulate the host plant’s resistance to pathogens.     

Plant K+ Channels: Similarity and Diversity

In this review we compared the electrophysiological properties of plant K⁺ uptake channels from different plants and tissues. Taking into account the detailed knowledge of K⁺ channel properties, which has emerged since the application of the patch-clamp technique on plant cells, as well as results from our recent studies we were able to extract features common among plant K⁺ channels. In addition, we focused on the diversity that could create plant or tissue-specificity. Functional fingerprints for the voltage-dependent K⁺ uptake channels were generated on the basis of their voltage-dependence, kinetics, permeability, conductance and pharmacology as well as regulation of K⁺ channels studied in their natural environment and cloned channels in heterologous expression systems. Finally, sequence information on plant and animal K⁺ channels cloned so far was used to identify structural motifs that may be related to functional phenotypes.