Symplast Volume, Turgor, Stomatal Conductance and Growth in Relation to Osmotic and Elastic Adjustment in Droughted Sugarcane1

Leaf water relations, stomatal conductance (g) and shoot growthrate (SGR) were monitored during a soil drying cycle in threesugarcane cultivars growing in pots in a greenhouse. The pressure-volumetechnique was used to evaluate diurnal and droughtinduced variationin leaf water relations characteristics. Leaf solute contentand bulk elasticity varied diurnally in both irrigated and droughtedplants and were highest at midday. Solute accumulation and increasedelasticity were also observed as leaf water deficits developedmore slowly during soil drying. This osmotic and elastic adjustmentmaintained symplast volume essentially constant both diurnallyand during soil drying, whereas turgor was only partially maintained.The extent of osmotic adjustment associated with drought wasnot reflected in the leaf osmotic potential at full turgor becausethe concurrent increase in tissue elasticity resulted in a largersymplast volume at full turgor. Cultivar responses over therange of leaf water deficits imposed did not provide conclusiveevidence for genotypic variation in osmotic and elastic adjustment.It appeared that behavioural differences in rates of water usemay have determined the magnitude of osmotic and elastic adjustmentin response to drought. In the early stages of soil drying,reductions in SGR and g were not accompanied by significantreductions in bulk leaf water status. This suggested that otherfactors, presumably signals originating from the roots, mayhave regulated SGR and g.     

Water-Relations Parameters of the Phloem. Determinations of Volumetric Elastic Modulus and Membrane Conductivity using an Applied Force Method and Shrinkage and Swelling of Tissues in Solutions at Differing Osmotic Pressure

Water-relations parameters were measured on sections of secondaryphloem from red oak (Quercus borealis michx. f.) and white ash(Fraxinus americana var. biltmoreana [Beadle] J. Wright) usinga linear displacement transducer. Changes in tissue thicknessin response to changes in the osmotic pressure of the bathingsolution were used to calculate the volumetric elastic modulusplus osmotic pressure (_v + ) of the tissue, and an applied forcemethod was used to estimate the time constant for water equilibration(T). The hydraulic conductivity of the cell membranes (L_p) wascalculated utilizing _v + and r values. The time-dependent behaviour of the tissue was much more complexthan originally expected. A correction for a time-dependentprocess that we call ‘drift’ was required to obtainnumbers for _v + . Furthermore, _v + was calculated on two assumptionsin order to relate changes in tissue dimensions to sieve elementparameters. In the first case, a lower limit for _v + of thesieve elements was determined by attributing all changes intissue dimensions to these cells. For red oak the average _v+ on this assumption is 72 bars. Assuming that all cell typeswere equally responsible for the changes in tissue dimensionsresulted in an _v + value of 192 bars for oak. If _v + and rare the same for all cells in the tissue, L_p for the sieve elementsof oak is 9.6 x 10^–8 cm s^–1 bar^–1. Exudationfrom the sieve elements of white ash during excision of thephloem led to artificially high values of _v + for that species. Quercus borealis michx. f., Fraxinus americana var, biltmoreana (Beadle) J. Wright, red oak, white ash, water relations, phloem, volumetric elastic modulus, membrane hydraulic conductivity     

A New Pressure Probe Method to Determine the Average Volumetric Elastic Modulus of Cells in Plant Tissue

A new in vivo method was used to determine an average volumetric elastic modulus ([epsilon]ave) for nongrowing cells in plant tissue. This method requires that both the relative transpiration rate, T, of the tissue and the average turgor pressure decay rate, (dP/dt)ave, of the cells are measured after the water source is removed from the plant tissue. Then [epsilon]ave is calculated from the equation [epsilon]ave = (-dP/dt)ave/T. This method was used to determine [epsilon]ave for cortical cells in stems of pea seedlings (Pisum sativum L.). The results demonstrate that [epsilon]ave increases from virtually zero at low P (approximately 0.01MPa) to approximately 10 MPa at high P (approximately 0.5 MPa). Analyses of the results indicate that the relationship between [epsilon]ave and P can be approximated by a linear function and more accurately approximated by a saturating exponential function: [epsilon]ave = [epsilon][infinity symbol][1 - exp {-k(P - Po)}], where Po is a plateau pressure (approximately 0.01 MPa), k is a rate constant (approximately 7 per MPa), and [epsilon][infinity symbol] (approximately 10 MPa) is the hypothetical maximum value of [epsilon]ave as P -> [infinity symbol]. Solutions for the turgor pressure decay (due to transpiration) as functions of time and symplasmic water mass (after the water source is removed) are derived.     

Ultrastructure of Dunaliella tertiolecta Cells Grown under Low and High CO2 Concentrations1

The cells of Dunaliella tertiolecta grown under ordinary air(low-CO₂ cells) had a well developed pyrenoid with many morestarch granules than those grown under air enriched with CO₂(high-CO₂ cells). The chloroplast was located close to the plasmamembranein low-CO₂ cells, while that in high-CO₂ cells was located inthe inner area of the cells. Chloroplast envelope was electronicallydenser in low-CO₂ cells than in high-CO₂ cells, while the oppositeeffect of CO₂ was observed for the plasmamembrane. ²On leave from Institute of Biology, University of Novi Sad,Novi Sad, Yugoslavia. (Received November 7, 1985; Accepted March 5, 1986)     

Two Polypeptides Inducible by Low Levels of CO2 in Soluble Protein Fractions from Chlorella regularis Grown at Low or High pH

Previous studies suggested that certain protein(s) other thancarbonic anhydrase might play an important role in the facilitatedtransport of dissolved inorganic carbon (DIC) from the mediumto the site of CO₂ fixation by ribulose-1,5-bisphosphate carboxylase/oxygenasein the unicellular green alga Chlorella regularis adapted tolow-CO₂ (ordinary air) conditions [Shiraiwa et al. (1991) Jpn.J. Phycol. 39: 355; Satoh and Shiraiwa (1992) Research in Photosynthesis,Vol. III, p. 779]. The proteins that might be involved in thisfacilitated transport of DIC were investigated by pulse-labelingof induced proteins with ³⁵S-sulfate during adaptation of cellsgrown under high-CO₂ conditions to low CO₂. Analysis by SDS-PAGErevealed that synthesis of two polypeptides, with molecularmasses of 98 and 24 kDa, respectively, was induced under low-CO₂conditions. The 24-kDa polypeptide was induced at pH 5.5 butnot at pH 8.0, whereas the 98-kDa polypeptide was induced atboth pH 5.5 and pH 8.0. The possible role of these polypeptidesin the facilitated transport of DIC in Chlorella regularis isdiscussed. (Received October 30, 1995; Accepted February 26, 1996)     

Turgor Regulation in a Brackish Charophyte, Lamprothamnium succinctum I. Artificial Modification of Intracellular Osmotic Pressure

Internodal cells of Lamprothamnium succinctum cultured in freshwater and brackish water of different salinities maintainedalmost the same turgor pressure at steady state. When the turgorpressure was increased by decreasing the external osmolality,the cells recovered their original turgor pressure within 2h. However, the recovery from decreased turgor pressure required1 day. When salts of the external medium were replaced with sorbitol,the cells still regulated the turgor pressure, indicating thatthe essential factor for the turgor regulation is not the salinitybut the osmolality. Internodal cells with osmotic pressure andion concentrations artificially modified to higher or lowervalues also regained the original turgor pressure by changingtheir intracellular osmotic pressure, whether the cells werecultured in brackish water or fresh water. These results indicate that turgor regulation is intrinsic toLamprothamnium and is initiated by a deviation of turgor pressurefrom the reference value, which is about 0.35 Osm. (Received November 28, 1983; Accepted March 14, 1984)     

Turgor, Growth and Rheological Gradients of Wheat Roots Following Osmotic Stress

The growth rate of hydroponically grown wheat roots was reducedby mannitol solutions of various osmotic pressures. For example,following 24 h exposure to 0·96 MPa mannitol root elongationwas reduced from 1· mm h^–1 to 0·1 mm h^–1 Mature cell length was reduced from 290 µm in unstressedroots to 100 µm in 0·96 MPa mannitol. This indicatesa reduction in cell production rate from about 4 per h in theunstressed roots to 1 per h in the highest stress treatment. The growing zone extended over the apical 4·5 mm in unstressedroots but became shorter as growth ceased in the proximal regionsat higher levels of osmotic stress. The turgor pressure along the apical 5·0 mm of unstressedroots was between 0·5 and 0·6 MPa but declinedto 0·41 MPa over the next 50 mm. Following 24 h in 0·48(200 mol m^–3) or 0·72 MPa (300 mol m^–) mannitol,turgor along the apical 50 mm was indistinguishable from thatof unstressed roots but turgor declined more steeply in theregion 5·10 mm from the tip. At the highest level ofstress (0·96 MPa or 400 mol m^–3 mannitol) turgordeclined steeply within the apical 20 mm. Key words: Growth, turgor pressure, wall rheology, osmotic stress, osmotic adjustment     

Radial Turgor and Osmotic Pressure Profiles in Intact and Excised Roots of Aster tripolium: Pressure Probe Measurements and Nuclear Magnetic Resonance-Imaging Analysis

High-resolution nuclear magnetic resonance images (using very short spin-echo times of 3.8 milliseconds) of cross-sections of excised roots of the halophyte Aster tripolium showed radial cell strands separated by air-filled spaces. Radial insertion of the pressure probe (along the cell strands) into roots of intact plants revealed a marked increase of the turgor pressure from the outermost to the sixth cortical layer (from about 0.1-0.6 megapascals). Corresponding measurements of intracellular osmotic pressure in individual cortical cells (by means of a nanoliter osmometer) showed an osmotic pressure gradient of equal magnitude to the turgor pressure. Neither gradient changed significantly when the plants were grown in, or exposed for 1 hour to, media of high salinity. Differences were recorded in the ability of salts and nonelectrolytes to penetrate the apoplast in the root. The reflection coefficients of the cortical cells were approximately 1 for all the solutes tested. Excision of the root from the stem resulted in a collapse of the turgor and osmotic pressure gradients. After about 15 to 30 minutes, the turgor pressure throughout the cortex attained an intermediate (quasistationary) level of about 0.3 megapascals. This value agreed well with the osmotic value deduced from plasmolysis experiments on excised root segments. These and other data provided conclusions about the driving forces for water and solute transport in the roots and about the function of the air-filled radial spaces in water transport. They also showed that excised roots may be artifactual systems.     

A Study of the Stationary Volumetric Elastic Modulus during Dehydration and Rehydration of Stems of Pea Seedlings

The relationship between cortical-cell turgor pressure (P) and tissue water mass (W) was determined for stem segments of pea (Pisum sativum L.) seedlings subjected to hydration and dehydration. This allowed a test for elastic hysteresis in the cortical cells. The P-W curves for dehydration and hydration were not coincident. In some experiments, the P-W curves exhibited a "roll-off" at high P, similar to the "plateau effect" sometimes observed in pressure-chamber studies. When hydration was followed by a 4-h dehydration, the tissue water mass (W0) at minimum turgor was reduced. This might reflect a reduction in apoplastic water mass and/or a contraction of the symplast during dehydration. Neglecting the decrease in W0 leads to underestimates of the stationary volumetric elastic modulus ([epsilon]stat). The result of an analysis that assumes W0 was constant during hydration suggests that there was no significant difference in [epsilon]stat between dehydration and hydration and, hence, no significant elastic hysteresis. However, a 16-h dehydration increased [epsilon]stat; this might be a response to water stress.     

High molecular weight lipids from the trilaminar outer wall (TLS)-containing microalgae Chlorella emersonii, Scenedesmus conmmunis and Tetraedron minimum

High molecular weight lipids were isolated from Chlorella emersonii, Scenedesmus communis and Tetraedron minimum, thin trilaminar outer wall (TLS)-containing freshwater microalgae producing an insoluble non-hydrolysable biopolymer (i.e. algaenan). Molecular weight determination by gel permeation chromatography indicated that their molecular weights range from ca. 400 to 2000 Da. Flash pyrolysis with in situ methylation using tetramethylammonium hydroxide (TMAH) and alkaline hydrolysis showed that the high molecular weight lipids isolated from C. emersonii and S. communis are mainly composed of saturated n-C26 and n-C28 fatty acids and alcohols and of saturated n-C30 and n-C32 alpha,omega-diols and omega-hydroxy acids. In contrast the high molecular weight lipids isolated from T. minimum are predominantly composed of long-chain fatty acids and omega-hydroxy acids. Aromatic moieties were also identified in small amounts in the thermochemolysate and in the hydrolysate. Chemical structural models containing long-chain mono- and polyesters were proposed for the high molecular weight lipids isolated from the three microalgae in agreement with analytical and spectroscopic data. Structural similarity between the outer cell wall of these microalgae and the cuticular membrane of higher plants is suggested.     

Influence of External Osmotic Pressure on Water Permeability and Electrical Conductance of Chara Cell Membrane

Water permeability of the plasma membrane of a Characean internodalcell decreased with an increase in the osmotic pressure of theoutside of the cell, suggesting that the equivalent pore radiusof the water-filled pores becomes smaller with an increase inthe osmotic pressure. In contrast, the apparent membrane resistancedid not increase with an increase in the external osmotic pressure.These facts suggest that ions pass through the membrane mainlyvia pores other than those for bulk water flow. (Received October 22, 1986; Accepted May 22, 1987)     

高静水压对小球藻的生理生化效应

对小球藻(Chlorella Vulgaris)进行高静水压处理,分别通过80MPa,300MPa静水压处理,观察高静水压处理时小球藻生理生化效应。实验结果表明,300MPa压力处理1h能够导致小球藻的大量死亡,少量存活的藻细胞经过5d的“停滞期”后开始正常生长。80MPa的压力下处理2h、6h、12h后小球藻的初期的生长速度明显加快,而到生长末期小球藻生长开始趋于平缓。小球藻干质量为12h实验组最大,而单位蛋白含量随着干质量的增加而下降,几种抗氧化酶活性为6h实验组具有最大活性。经过300MPa压力预处理1h后的小球藻再在80MPa压力下进行处理,发现小球藻干质量为2h再处理实验组最大,蛋白含量为6h再处理实验组最高,抗氧化酶的活性随着压力处理时间的增加而下降。     

Mode of Action of Nisin Z against Listeria monocytogenes Scott A Grown at High and Low Temperatures

Nisin Z, a natural nisin variant, was recently isolated from Lactococcus lactis subspecies lactis NIZO 22186. The gene for this lantibiotic, designated nisZ, has been cloned, and its nucleotide sequence was found to be identical to that of the precursor nisin gene with the exception of a single mutation resulting in the substitution of Asn-27 for His-27 in the mature polypeptide (J. W. M. Mulders, I. J. Boerrigter, H. S. Rollema, R. J. Siezen, and W. M. de Vos, Eur. J. Biochem. 201:581-584, 1991). A K⁺ electrode was used to investigate the effect of various environmental parameters on the action of nisin Z against Listeria monocytogenes. Addition of nisin Z resulted in immediate loss of cell K⁺, depolarization of the cytoplasmic membrane, inhibition of respiratory activity, and hydrolysis and partial efflux of cellular ATP. The action of nisin Z was optimal at pH 6.0 and was significantly reduced by di- and trivalent cations. The lanthanide gadolinium (Gd³⁺) was an efficient inhibitor and prevented nisin Z activity completely at a concentration of 0.2 mM. Nisin Z-induced loss of cell K⁺ was reduced at low temperatures, presumably as a result of the increased ordering of the lipid hydrocarbon chains in the cytoplasmic membrane. In cells grown at 30°C, the action of nisin Z was prevented below 7°C, whereas in cells grown at 4°C nisin Z was able to induce K⁺ leakage at this low temperature.     

Quantification of the Contribution of CO2, HCO3-, and External Carbonic Anhydrase to Photosynthesis at Low Dissolved Inorganic Carbon in Chlorella saccharophila

cDNAs encoding the large subunit and a possibly truncated small subunit of the potato tuber (Solanum tuberosum L.) adenosine 5'-diphosphate-glucose pyrophosphorylase have been expressed in Escherichia coli (A.A. Iglesias, G.F. Barry, C. Meyer, L. Bloksberg, P.A. Nakata, T. Greene, M.J. Laughlin, T.W. Okita, G.M. Kishore, J. Preiss, J Biol Chem [1993] 268: 1081-1086). However, some properties of the transgenic enzyme were different from those reported for the enzyme from potato tuber. In this work, extension of the cDNA was performed to elongate the N terminus of the truncated small subunit by 10 amino acids. This extension is based on the almost complete conservation seen at the N-terminal sequence for the potato tuber and the spinach leaf small subunits. Expressing the extended cDNA in E. coli along with the large subunit cDNA yielded a transgenic heterotetrameric enzyme with similar properties to the purified potato tuber enzyme. It was also found that the extended small subunit expressed by itself exhibited high enzyme activity, with lower affinity for activator 3-phosphoglycerate and higher sensitivity toward inorganic phosphate inhibition. It is proposed that a major function of the large subunit of adenosine 5'-diphosphate-glucose pyrophosphorylases from higher plants is to modulate the regulatory properties of the native heterotetrameric enzyme, and the small subunit's major function is catalysis.     

Photosynthetic Carbon Metabolism in Photoautotrophic Cell Suspension Cultures Grown at Low and High CO(2)

Photosynthetic carbon metabolism was characterized in four photoautotrophic cell suspension cultures. There was no apparent difference between two soybean (Glycine max) and one cotton (Gossypium hirsutum) cell line which required 5% CO₂ for growth, and a unique cotton cell line that grows at ambient CO₂ (660 microliters per liter). Photosynthetic characteristics in all four lines were more like C₃ mesophyll leaf cells than the cell suspension cultures previously studied. The pattern of ¹⁴C-labeling reflected the high ratio of ribulosebisphosphate carboxylase to phosphoenolpyruvate carboxylase activity and showed that CO₂ fixation occurred primarily by the C₃ pathway. Photorespiration occurred at 330 microliters per liter CO₂, 21% O₂ as indicated by the synthesis of high levels of ¹⁴C-labeled glycine and serine in a pulse-chase experiment and by oxygen inhibition of CO₂ fixation. Short-term CO₂ fixation in the presence and absence of carbonic anhydrase showed CO₂, not HCO₃⁻, to be the main source of inorganic carbon taken up by the low CO₂-requiring cotton cells. The cells did not have a CO₂-concentrating mechanism as indicated by silicone oil centrifugation experiments. Carbonic anhydrase was absent in the low CO₂-requiring cotton cells, present in the high CO₂-requiring soybean cell lines, and absent in other high CO₂ cell lines examined. Thus, the presence of carbonic anhydrase is not an essential requirement for photoautotrophy in cell suspension cultures which grow at either high or low CO₂ concentrations.     

The Interrelations of Cell Turgor Pressure, Gas-vacuolation, and Buoyancy in a Blue-green Alga

The increase in pressure required to collapse gas vacuoles onsuspending the cells of the blue-green alga Anabaena flos-aquaein hypertonic sucrose solutions shows the turgor pressure tovary over the range of 265 to 459 KN m^–2 under differentculture conditions. The cell turgor increased at a rate of upto KN m^–2 h^–1 on transferring the alga from lowto high light intensity. This rise appears to be a result ofthe accumulation of photosynthate, as it is dependent on thepresence of carbon dioxide in the gas phase and is inhibitedby DCMU. Experiments using ¹⁴CO² indicate that the increasedrate of photosynthesis during the high light exposure is easilysufficient to account for the observed turgor rise. The rise in turgor can bring about collapse of sufficient ofthe alga's gas vacuoles to destroy its buoyancy. Higher turgorpressures, and consequently a lower degree of gas vacuolationand buoyancy, were maintained when the alga was kept at highlight intensitives for a week and more. The significance ofthis behaviour is discussed in relation to stratification ofplanktonic blue-green algae in natural habitats.     

Water Relations of Growing Maize Coleoptiles : Comparison between Mannitol and Polyethylene Glycol 6000 as External Osmotica for Adjusting Turgor Pressure

Water relations of growing segments of maize (Zea mays L.) coleoptiles were investigated with osmotic methods using either mannitol (MAN) or polyethylene glycol 6000 (PEG) as external osmotica. Segments were incubated in MAN or PEG solutions at 0 to - 15 bar water potential (Ψ_o) and the effects were compared on elongation growth, osmotic shrinkage, cell sap osmolality (OC), and osmotic pressure (π_i). The nonpenetrating osmoticum PEG affects π_i in agreement with Boyle-Mariotte's law, i.e. the segments behave in principle as ideal osmometers. There is no osmotic adjustment in the Ψ_o range permitting growth (0 to −5 bar) nor in the Ψ_o range inducing osmotic shrinkage (−5 to −10 bar). Promoting growth by auxin (IAA) has no effect on the osmotic behavior of the tissue toward PEG. In contrast to PEG, MAN produces an apparent increase in π_i accompanied by anomalous effects on segment elongation and shrinkage leading to a lower value for Ψ_o which establishes a growth rate of zero and to an apparent recovery from osmotic shrinkage after 2 hours of incubation. These effects can be quantitatively attributed to uptake of MAN into the tissue. MAN is taken up into the apoplastic space and the symplast as revealed by a large temperature-dependent component of MAN uptake. It is concluded that MAN, in contrast to PEG, is unsuitable as an extemal osmoticum for the quantitative determination of water relations of growing maize coleoptiles.     

Photosynthetic Performance of Ginkgo biloba L. Grown Under High and Low Irradiance

Diurnal variation in net photosynthetic rate (P _N) of three-year-old plants of Ginkgo biloba was studied under open, O (receiving full sunlight), net-shade, NS (40 % of photosynthetically active radiation, PAR), or greenhouse, G (25 % PAR) conditions. In all three conditions, P _N was higher in morning along with stomatal conductance (g _s), and intercellular CO₂ concentration (C _i), while leaf temperature and vapour pressure deficit were low. The O-plants exhibited a typical decline in P _N during midday, which was not observed in NS-plants. This indicated a possible photoinhibition in O-plants as the ratio of variable to maximum fluorescence (F_v/F_m) and photosystem 2 (PS2) yield (_PS2) values were higher in the NS- and G-plants. On the contrary, stomatal density and index, chlorophyll a/b ratio, leaf thickness, and density of mesophyll cells were greater in O-plants. Further, higher P _N throughout the day along with higher relative growth rate under NS as compared to O and G suggested the better efficiency of Ginkgo plants under NS conditions. Therefore, this plant species could be grown at 40 % irradiance to meet the ever-increasing demand of leaf and also to increase its export potential.     

Effects of High Pressure Treatment on the Ultrastructure and Solubilization of Isolated Myofibrils

High hydrostatic pressures of 100 MPa to 300 MPa were applied to isolated myofibrils prepared from rabbit skeletal muscle to investigate the pressure-induced degradation of myofibrillar structure in the muscle.

A marked loss of the regular structure was observed in the phase-contrast image of the isolated myofibrils pressurized at 150 MPa, with further progress of the rupture of structure with increasing pressure applied. When exposed to pressures of 200 MPa or higher, clumping of the crushed myofibrils was observed. Electron microscopic studies of the pressurized myofibrils showed that the loss of M-line materials, rupture of I-filament, and the loss of the structural continuity with the loss of Z-line progressed in the myofibrils with increasing pressure applied. A sigmoidal relationship was obtained between the degree of solubilization and the intensity of the pressure applied to the isolated myofibrils. The electrophoretic analysis indicated that the amount and the species of the protein released from the myofibrils at each stage of the pressurization corresponded to the disruption of the ultrastructure in the myofibrils.