Freezing stress and membrane injury of Norway spruce (Picea abies) tissues

Effects of sub-zero temperatures (−5 to −35°C) on the tissues of needles, buds and shoots of Norway spruce [ Picea abies (L.) Karst.] were studied. The freezing caused increased efflux of cellular electrolytes. Freezing injury of the primordial shoots and 1-year-old shoots was the result of the spontaneous freezing of a deep supercooled cellular water. The crystallization injures the cellular membranes leading to the loss of semipermeability and to the drastic efflux of K⁺. In the needles there was no deep supercooling of water and two patterns of changes in the membranes, depending upon the range of the applied temperatures, could be distinguished. At 0 to – 25°C, which do not kill the cells, we observed a disturbance in the membrane semipermeability as monitored by electrolytes efflux within a few hours after thawing of the needles. At lower temperatures (−35°C) we observed irreversible loss of the membrane semipermeability, and death of the tissue. Those changes occurred 10 h after thawing and were probably caused by the released lytic enzymes and some toxic compounds, which acted on the cellular membranes.     

Plasma membrane transport systems in higher plants: From black boxes to molecular physiology

Considerable progress in identifying transport systems of the plant plasma membrane has been made recently. The putative systems cloned to date comprise H⁺-ATPases, potassium, chloride and water channels, and carriers involved in the transport of glucose, sucrose, amino acids, peptides, potassium, nitrate, ammonium, phosphate, sulfate, iron and copper. Most of these systems were identified first in Arabidopsis thaliana . Successful cloning strategies have involved the following variety of techniques: complementation of yeast mutants, screening of Arabidopsis mutants, immunoscreening of a cDNA expression library expressed in mammalian cells, screening of genomic and cDNA libraries with probes (or degenerate oligonucleotides) derived from yeast and/or animal genes, or database screening for sequence similarity to eukaryotic counterparts. Many related transport systems have subsequently been identified either by screening libraries directly, or by systematic cDNA sequencing programs. Surprisingly large gene families have been revealed. Heterologous expression systems, such as yeast, Xenopus oocytes or insect cells, provide tools for studying the transport activities, biochemical properties and structure-function relationships of these systems. Their expression and functions in planta are investigated using northern blot analysis, in situ hybridization, and transgenic approaches. Individual systems encoded by the same gene family can differ in their transport properties and have distinct tissue expression patterns. Such diversity might be central to the integration of solute transport at the whole plant level, allowing the differential expression of sets of transport systems specifically tailored to the requirements of each tissue.     

Transport of hydrophobic ions in erythrocyte membrane: I. Zero membrane potential properties

Summary The permeability and partition coefficients of tetraphenylarsonium (TPA) and several other organic cations were studied in the human erythrocyte using an ion-selective electrode. The permeability constant for the different cations could be explained quite well by differences in oil/water partition coefficients. No evidence for facilitated transport could be found. Binding of the organic ions occurred to both the cell membrane and to intracellular contents. Partitioning to the membrane remained relatively constant despite variation from ion intracellular binding with blood samples from different donors. TPA flux is stimulated by substoichiometric amounts of tetraphenylboron and other organic anions, suggesting an ion-pairing mechanism.     

Constant change: dynamic regulation of membrane transport by calcium signalling networks keeps plants in tune with their environment

Despite substantial variation and irregularities in their environment, plants must conform to spatiotemporal demands on the molecular composition of their cytosol. Cell membranes are the major interface between organisms and their environment and the basis for controlling the contents and intracellular organization of the cell. Membrane transport proteins (MTPs) govern the flow of molecules across membranes, and their activities are closely monitored and regulated by cell signalling networks. By continuously adjusting MTP activities, plants can mitigate the effects of environmental perturbations, but effective implementation of this strategy is reliant on precise coordination among transport systems that reside in distinct cell types and membranes. Here, we examine the role of calcium signalling in the coordination of membrane transport, with an emphasis on potassium transport. Potassium is an exceptionally abundant and mobile ion in plants, and plant potassium transport has been intensively studied for decades. Classic and recent studies have underscored the importance of calcium in plant environmental responses and membrane transport regulation. In reviewing recent advances in our understanding of the coding and decoding of calcium signals, we highlight established and emerging roles of calcium signalling in coordinating membrane transport among multiple subcellular locations and distinct transport systems in plants, drawing examples from the CBL‐CIPK signalling network. By synthesizing classical studies and recent findings, we aim to provide timely insights on the role of calcium signalling networks in the modulation of membrane transport and its importance in plant environmental responses.     

Alterations of wheat root plasma membrane lipid composition induced by copper stress result in changed physicochemical properties of plasma membrane lipid vesicles

A response when wheat is grown in excess copper is an altered lipid composition of the root plasma membrane (PM). With detailed characterisation of the root PM lipid composition of the copper-treated plants as a basis, in the present study, model systems were used to gain a wider understanding about membrane behaviour, and the impact of a changed lipid composition.PMs from root cells of plants grown in excess copper (50 μM Cu²⁺) and control (0.3 μM Cu²⁺) were isolated using the two-phase partitioning method. Membrane vesicles were prepared of total lipids extracts from the isolated PMs, and also reference vesicles of phosphatidylcholine (PC). In a series of tests, the vesicle permeability for glucose and for protons was analysed. The vesicles show that copper stress reduced the permeability for glucose of the lipid bilayer barrier. When vesicles from stressed plants were modified by addition of lipids to resemble vesicles from control plants, the permeability for glucose was very similar to that of vesicles from control plants. The permeability for protons did not change upon stress.Electron paramagnetic resonance (EPR) of the lipid vesicles spin probed with n-doxylstearic acid (nDSA) was used to explore the lipid rotational freedom at different depth of the bilayer. The EPR measurements supported the permeability data, indicating that the copper stress resulted in more tightly packed bilayers of the PMs with reduced acyl chain motion.     

Contribution of Oxidative Stress to the Development of Cold-Induced Damage to Leaves of Chilling-Sensitive Plants: 3. Injury of Cell Membranes by Chilling Temperatures

Changes in permeability of cell membranes (judged from electrolyte leakage) were examined on leaves of 7- to 11-day-old seedlings of maize (Zea mays L.), cucumber (Cucumis sativus L.), millet (Panicum miliaceum L.), and on etiolated shoots of potato (Solanum tuberosum L.) immediately after cooling plants for 1–24 h at 2°C and one day after a 24-h chilling treatment. A gradually increasing leakage of ions from the cells was observed upon prolongation of chilling exposure, with the maximum attained by the end of 24-h chilling treatment. The leakage of electrolyte was slightly reduced in the post-treatment period but it was still higher than the electrolyte leakage from the control samples (untreated plants). The cold treatment of chilling-sensitive plants (but not of potato) revealed a positive correlation between the rates of lipid peroxidation, indicative of chilling injury, and the electrolyte efflux (r = 0.61–0.96). The evaluation of plant susceptibility to injury showed that millet and potato plants recovered from the chilling damage in 24 h after the treatment, whereas maize and cucumber plants did not show such a recovery.