Epidermal Bladder Research Articles

Tissue-specific expression and functional complementation of a yeastpotassium-uptake mutant by a salt-induced ice plant gene mcSKD1

A full-length salt-induced transcript homologous to SKD1 (suppressor of K(+) transport growth defect) of the AAA (ATPase associated with a variety of cellular activities)-type ATPase family has been identified from the halophyte Mesembryanthemum crystallinum (ice plant). The expression of mcSKD1 was induced by 200 mM NaCl or higher in cultured ice plant cells. When cultured ice plant cells were grown in a high K(+) (42.6 mM) medium, the level of mcSKD1 expression decreased. At the whole plant level, constitutive expression of mcSKD1 was observed in roots, stems, leaves and floral organs. Addition of 400 mM NaCl increased the transcript level in roots and stems. The expression of atSKD1 , a homologue gene in Arabidopsis , was down regulated by salt stress. Under salt stress, mcSKD1 was preferentially expressed in the outer cortex of roots and stems and in the epidermal bladder cells of leaves. The mcSKD1 transcript was constitutively expressed in placenta and integuments of the developing floral buds. Expression of the full-length or C-terminal deletion of mcSKD1 was able to complement the K(+) uptake-defect phenotype in mutant Saccharomyces cerevisiae , which is defective in high- and low-affinity K(+) uptake. Deletion of the N-terminal coiled-coil motif of mcSKD1, a structure required for membrane association, resulted in greatly reduced K(+) transport. Expression of mcSKD1 also increased the salt-tolerant ability of yeast mutants and either N- or C-terminal deletion decreased the efficiency. The physiological relevancies of mcSKD1 for K(+) uptake under high salinity environments are discussed.

Spectral dependence of flavonol and betacyanin accumulation in Mesembryanthemum crystallinum under enhanced ultraviolet radiation

Abstract Mesembryanthemum crystallinum L. (Aizoaceae) is a drought‐ and salt‐tolerant halophyte that is able to endure harsh environmental conditions. Upon irradiation with high light irradiance (1200–1500 µmol m−2 s−1) it displays a rapid cell‐specific accumulation of plant secondary metabolites in the upper leaf epidermis; a phenomenon that is not detectable with salt or drought treatment. The accumulation of these compounds, the betacyanins and acylated flavonol glycosides, increases if the plants are exposed to polychromatic radiation with a progressively decreasing short‐wave cut‐off in the ultraviolet range. The response is localized in the epidermal bladder cells on the tips of young leaves and epidermal layers of fully expanded leaves. It is demonstrated that the accumulation of flavonols and betacyanins can be described by a weakly sigmoid dose function in combination with an exponential decrease of the response function of the plant with increasing wavelength.

The expression of HAK-type K(+) transporters is regulated in response to salinity stress in common ice plant.

Four transcripts homologous to K(+) transporters of the HAK/KT/KUP family have been characterized from the common ice plant (Mesembryanthemum crystallinum). We report tissue-specific expression of McHAK1 and McHAK4 transcripts abundant in roots, leaves, and stems. McHAK2 was predominantly present in stems and McHAK3 in root tissues. By in situ hybridizations, the McHAKs showed signals in the leaf vascular bundles, mesophyll, and epidermal cells as well as in epidermal bladder cells. In mature roots, transcripts were mainly localized to the vasculature, and in differentiated root tips, the strongest signals were obtained from the epidermis. Expression of McHAK1, McHAK2, and McHAK4 complemented a yeast mutant defective in low- and high-affinity K(+) uptake. Growth of the yeast mutant was restored at low-millimolar K(+) concentrations and was inhibited by Rb(+) and Cs(+) but was not affected by Na(+). Transcript levels of McHAK1 and McHAK4 increased by K(+) starvation and by salt stress of 400 mM NaCl in leaves and roots. Expression of McHAK2 and McHAK3 was stimulated in leaves and was transiently induced in roots in response to high salinity with prestress transcript levels restored in salt-adapted plants. We discuss possible roles for such transporters in ion homeostasis at high salinity.

Na+/H+ exchange in the halophyte Mesembryanthemum crystallinum is associated with cellular sites of Na+ storage.

The tonoplast Na+/H+ exchanger is involved in sequestering Na+ in plant vacuoles, providing solutes for osmotic adjustment while avoiding cytoplasmic Na+ toxicity. As such it is assumed to be one of the key mechanisms involved in salt-tolerance in plants. In this study, we measured tonoplast Na+/H+ exchange in roots and different leaf tissues of adult Mesembryanthemum crystallinum L. plants to determine if activity of the exchanger follows the gradient from roots to leaves previously observed for Na+ and pinitol accumulation. Na+/H+ exchange was absent from roots of control and NaCl-treated plants. In contrast, leaves showed constitutive Na+/H+ exchange that was enhanced by growth of the plants in NaCl. Highest activity was measured in the epidermal bladder cells in agreement with the highest concentrations of Na+ found in this tissue. Tonoplast H+-translocating ATPase activity was also greatest in this tissue, as were protein levels for myo-inositol-O-methyltransferase, a key enzyme in the pinitol biosynthesis pathway. The strong correlation between Na+/H+ exchange and Na+ accumulation confirms the role of this transporter in vacuolar sequestration of Na+ and plant salt tolerance.

Growth and development of Mesembryanthemum crystallinum (Aizoaceae).

This review describes the life cycle of Mesembryantheum crystallinum L. (the common ice plant, Aizoaceae, Caryophyllales), a halophyte with a developmentally programmed switch from C3 photosynthesis to Crassulacean acid metabolism (CAM) which is accelerated by salinity and drought. Since there has been controversy regarding the interplay between genes and environmental stimuli during the development of M. crystallinum, it is timely to summarize the life cycle for a defined set of conditions. We seek to establish the framework whereby five stages of development can be described in terms of morphology, physiology, and molecular biology. Stages 1 and 2, representing germination and growth of a juvenile form, show a determinate pattern of growth. Although specific genes for salt tolerance can be induced at these stages, stress early in development prevents progression to the mature form (stages 3-5) in which the plants advance to mature growth, flowering, and seed development. Growth in stage 3 is indeterminate in the absence of stress, but development and flowering are accelerated by environmental stresses, and CAM is constitutively expressed. Depending on the severity of the stress, plants start to flower (stage 4) and then die from the roots, ultimately with only seed capsules remaining viable, with salt sequestered into large epidermal bladder cells (stage 5). We highlight responses to salinity leading to compartmentation of ions and compatible solutes, turgor maintenance, and CAM. Finally, the molecular genetics of the ice plant are characterized, emphasizing selected genes and their products. We conclude with an analysis of the multiple stages of growth as an ecological adaptation to progressive stress. The initial determinate and inflexible juvenile phase provides a critical mass of plant material which supports the indeterminate, mature phase. Depending on the degree of stress, the mature form is then propelled towards flowering and seedset. CONTENTS Summary 171 I. Introduction 172 II. Standardizing methodology 173 III. Growth and development 175 IV. Effects of salt stress on developmental physiology 176 V. Ionic composition of cells during development 179 VI. Water transport within the plant 179 VII. The switch from C3 to Crassulacean Acid Metabolism 181 VIII. Stress and plant-growth regulators 182 IX. Molecular biology 183 X. Genetics, ploidy and mutants 184 XI. Conclusions and future directions 185 Acknowledgements 187 References 187.

Salt Secretion in some Chenopodium Species

Salt secretion to epidermal bladder hairs was investigated in Chenopodium album L., Ch. giganteum D on and Ch. murale L. after treatment with 100 mmol. I −1 NaCl in culture solution. In all three species, chloride concentration in the vacuole of the bladders exceeds the chloride concentration in the leaf lamina. In Ch. album and Ch. giganteum double mesophyll concentration may be reached in the bladders. Ion accumulation in bladder hairs is usually described by accumulation ratios. This figure does not change in the course of leaf development with respect to chloride. In sodium and potassium, however, it changes with time, probably because of changes in water content of the bladders and changes in ion concentration in mesophyll cells. Therefore, consideration of average accumulation ratios, including older leaves, still with intact bladders, does not necessarily give the real amount of secretion capacity. Salt regulation by bladder hairs of Chenopodium species can be almost neglected because of their minimal volume in relation to the remaining plant tissues. Nevertheless, comparative studies of Chenopodium , and Atriplex bladders can contribute much to the general understanding of this secretion process.

Day/night variations in turgor pressure in individual cells of Mesembryanthemum crystallinum L.

Using a pressure probe, turgor pressure was directly determined in leaf-mesophyll cells and the giant epidermal bladder cells of stems, petioles and leaves of the halophilic plant Mesembryanthemum crystallinum. Experimental plants were grown under non-saline conditions. They displayed the photosynthetic characteristics typical of C3-plants when 10 weeks old and performed weak CAM when 16 weeks old. In 10 week old plants, the turgor pressure (P) of bladder cells of stems was 0.30 MPa; of bladder cells of petioles 0.19 MPa, and of bladder cells of leaves 0.04 MPa. In bladder cells from leaves of 16 week old plants, marked changes in turgor pressure were observed during day/night cycles. Maximum turgor occurred at noon and was paralleled by a decrease in the osmotic pressure of the bladder cell sap. Similar changes in the cell water relations were observed in plants in which traspirational water loss was prevented by high ambient relative humidity. Turgor pressure of mesophyll cells also increased during day-time showing macimum values in the early morning. No such changes in turgor pressure and osmotic pressure were observed in bladder and mesophyll cells of the 10 week old plants not showing the diurnal acid fluctuation typical of CAM.

Water relations of the epidermal bladder cells ofOxalis carnosa Molina

All of the cells of the upper (adaxial) epidermis of the leaves ofOxalis carnosa are transformed into large bladders, while in the lower epidermis the bladder cells are interrupted by "normal" cells with stomata. The epidermal bladders contain a high concentration of free oxalic acid (pH approx. 1). Water-relations parameters of these epidermal bladder cells have been determined using the pressure probe. Original cell turgor (P0) of the closely packed bladders of theupper epidermis was P0=0.7 to 2.9 bar ([Formula: see text]; mean±SD;N=25 cells) and lower than that in the club-shaped bladders of thelower epidermis (P0=1.3 to 3.7 bar;[Formula: see text];N=25 cells). Large differences in the elastic modulus (ε) and the hydraulic conductivity (Lp) of the two different types of cells were observed. For the lower epidermal bladders, ε=18 to 166 bar and was similar to that of other higher plant cells. Also, for these cells it was found that ε was increasing with both, cell turgor and cell volume. By contrast, ε of the cells of the upper epidermis was by one order of magnitude smaller (ε=1.9 to 17.0 bar) and no dependence of ε on cell volume could be detected. The Lp values of the cell membranes were also different (lower epidermis:[Formula: see text]; upper epidermis:[Formula: see text]). These differences seem to be too large to be caused by errors in determining the exchange area for water (A) between cells and adjacent tissue. The half-times of water exchange between bladders and leaf (T1/2) were, on average, somewhat longer for the upper than for the lower epidermis (lower epidermis: T1/2=7 to 38 s; upper epidermis: T1/2=22 to 213 s), but the differences in the T1/2 values were not as distinct as for ε and Lp. This is because of the compensatory effects of ε, Lp and the different ratios of volume to exchange area. Since the bladders make up about 75% of the entire volume of the leaf, it is assumed that the rate of response of the leaf to changes in the water potential should be similar to that of the bladder cells. The results are discussed in terms of a possible function of the bladders in the leaf.

Cell Surface Antigens in Normal and Neoplastic Urinary Bladder Epithelial Cells of the Rat<xref ref-type="fn" rid="FN2">2</xref>

Cell surface antigens of normal urinary bladder epithelium (NBE) and bladder cancers of inbred ACI/N rats were assayed by antisera raised in rabbits. Mixed hemadsorption test combined with absorption analysis defined three kinds of cell surface antigens in both NBE and bladder cancer cells; the first antigen was common to lymphoid cells, the second was present in most of the epithelia, and the third was unique to NBE and present to a lesser extent in bladder cancers. In addition, bladder cancers had a fourth antigen that was common only to epidermis. These findings were confirmed by the use of typing sera for the third and the fourth antigens, which were prepared by absorptions of each antiserum with lymphoid cells and the lung. Direct titration of the typing sera against various cells revealed that the third antigen (NBE antigen) was species-specific and the fourth antigen (BC-SK antigen) was not common to human bladder cancers but common in part to mouse epidermal cells and bladder cancers.

Ultrastructural Observations on Developing Leaf Bladder Cells of Mesembryanthemum crystallinum L.

The surface of leaves and stems of the halophyte Mesembryanthemum crystallinum are covered by epidermal bladder cells with a volume frequently larger than mm3. The differentiation of these cells has been studied electron microscopically with special regard to the formation of the large central vacuole. Large numbers of cisternae of rough endoplasmic reticulum were observed in all stages and seem to form provacuoles. The possibility is discussed, that the ER represents an intraplasmatic compartment for transport of ions and possibly of organic solutes, necessary to build up the hydrostatic pressure required for growth to the bladder cells.

Membrane potentials and salt distribution in epidermal bladders and photosynthetic tissue of Mesembryanthemum crystallinum L.

Abstract Membrane potentials (pd's) of epidermal bladder cells and green leaf cells of Mesembryanthemum crystallinum L. are rather low (between −10 and −40 mV). During growth on 400 mM NaCl membrane potentials decrease further. As shown previously, plants grown on 400 mM NaCl show the diurnal changes of malate levels typical for plants having crassulacean acid metabolism. Therefore, in this study membrane potentials were measured at different times of the day, but no diurnal variations of pd were correlated with diurnal oscillations of malate levels. Resting potentials are similar in bladder cells and in green leaf cells and are similar in continuous light and darkness. Both bladder and leaf cells display light‐triggered photosynthesis‐dependent oscillations of the membrane potential although the bladder cells do not appear to be photosynthetically very active. This suggests electrical coupling between the bladder cells and the underlying green cells. Over a larger distance (2 mm) in the leaves, however, there is no direct evidence for electrical coupling. Cl−, Na+, and K+ concentrations are similar in bladder cells and in the photosynthetically active tissue of leaves and stems. Bladder cells appear to contain high concentrations of free oxalate. The present findings corroborate earlier conclusions that the epidermal bladder cells of M. crystallinum function as peripheral water reservoirs providing protection from short term water stress.

Effect of Turgor Pressure and Cell Size on the Wall Elasticity of Plant Cells

Direct measurements of the volumetric elastic modulus, in, of cells of a higher plant were performed on the epidermal bladder cells of Mesembryanthemum crystallinum using a pressure probe technique. Measurements on giant algal cells (Valonia, Nitellopsis) are given for comparison. Giant celled algae and M. crystallinum bladders have elastic moduli, in, which depend strongly on turgor pressure, P, and on cell volume, V. The in values of Mesembryanthemum bladders range between 5 bar at zero pressure and 100 bar at full turgor pressure (3-4 bar). in increased with cell size (volume) at a given turgor pressure, and this volume dependence was pronounced more in the high pressure range. From the in (P) characteristics, complete volume-pressure curves were obtained for Mesembryanthemum bladders and giant algal cells. The results suggest that the in (P) and in (V) characteristics of all plant cells are similar. The significance of the pressure and volume effects for the water relations and growth processes of plant cells is discussed briefly.

Water relations of the epidermal bladder cells of the halophytic species Mesembryanthemum crystallinum: Direct measurements of hydrostatic pressure and hydraulic conductivity

Water exchange between the bladder cells of stems of the halophytic species Mesembryanthemum crystallinum and the subepidermal cortical cell layers was determined by direct cell turgor pressure measurements using a pressure probe. Treating the system bladder cell/subepidermal cortex as two homogeneous elastic compartments the hydraulic conductivity, L p, of the barrier separating both compartments was found to be L p=2·10(-6) cm ·s(-1)·bar(-1). As discussed, this value essentially reflects the hydraulic conductivity of the bladder cell membrane, which is unusually high compared with the values expected for higher plant cells. The L p-values did not show a dependence on cell turgor pressure over a large pressure range (0.1 to 6 bar) nor on the salinity of the bladder sap (osmolarity range: 500 to 1700 mOsmol). Furthermore, the stationary pressure-values obtained in the pressure-flow experiments point to unusually high permeabilities of the bladder membrane to electrolytes (KCl and NaCl). The unique transport properties of the bladder cell membrane for salt and water suggest a special physiological function of the bladders in the water economy of the plant. It is assumed that the bladders form a reservoir for salts and water in the plant which upon osmotic stress acts as a buffering system to protect the photosynthetic tissue from osmotic injury.