Interrelationships between water and cellular metabolism inArtemia cysts

Cysts of the crustaceanArtemia are a useful model for studies on intracellular water because they are capable of essentially complete and reversible desiccation. We have used a variety of techniques on this system, the present work being an attempt to estimate the density of intracellular water (ρ_w). The density of individual cysts was evaluated from sedimentation velocity. Heptane displacement methods were used to determine the volume of a known mass of cysts, from which the density was calculated. The two methods produce comparable results. It was shown that the densities and water contents of large masses of cysts accurately reflect those of individual cysts. Cyst densities (ρ_c) were determined over the entire range of water content from 0 to 0.63 weight fraction of water (W _f), and temperature dependence was measured for 0.61W _f over 2–41°C. The following refer to 25°C. No marked change was detected in ρ_c until the water content exceeded 0.15W _f, at which ρ_c decreased as a linear function of Wf to maximum water content. However, the cyst does not behave ideally in the sense that the densities of the nonaqueous components and added water are not additive as a function ofW _f. The partial specific volume of water in cysts at maximum hydration was estimated to be 3% larger than that of pure water. These observations are compared with density measurements on other systems, and with previous findings on the physical properties of water in this system.     

Microscopic contributions to the pressure-volume diagram of the cell-water relations as demonstrated with tissue cells

Summary Continuing microscopic studies on cell-water relations with single cells (Gerdenitsch 1979) based on the relationship between the osmotic potential and the cell water volume, tissue cells were investigated. The experiments were done with inner epidermis of the bulb scale of onion (Allium cepa) which seemed to be most suitable for those investigations. Using a diagram described byRichter (1978) pressure volume curves of cells at the margin of the epidermis pieces neighboured by a various amount of dead cells and of cells in the center of tissue were worked out. They were contributed to one of three groups according to their amount of free surface (group 1: >1/3 free surface, group 2: <1/3 free surface, group 3: cells surrounded only by living-cells). Curves of the mean values of each of the three groups were compared as well as the mean -values, calculated as a measure for the elasticity of the cell wall.It was found that cells surrounded only by living cells had -values less than with both other groups. Assuming from observations during the experiments that all cells had very similar properties, this difference could be attributed to the expression of the effect of tissue counterpressure.     

Inhibited light activation of fructose and sedoheptulose bisphosphatase in spinach chloroplasts exposed to osmotic stress

The light activation of fructose-1,6-bisphosphatase (EC 3.1.3.11) and sedoheptulose-1,7-bisphosphatase (EC 3.1.3.37) was inhibited in isolated intact spinach (Spinacia oleracea L.) chloroplasts exposed to reduced osmotic potentials. Decreases in the velocity and magnitude of light activation correlated with the overall reduction in CO₂ fixation rates. Responses of osmotically stressed chloroplasts to both varying pH and exogeous dihydroxyacetone phosphate (DHAP) or 3-phosphoglycerete (PGA) were examined. In the presence of DHAP, the absolute rate of CO₂ fixation was increased and this increase was most pronounced at alkaline pH. Enhanced light activation of these enzymes was also observed under these conditions. However, in the presence of PGA, similar increases in photosynthetic rate and enzyme activation were not evident. Light-dependent stromal alkalization was unaffected by the stress treatments. Inhibition of light activation under hypertonic conditions is discussed in terms of substrate availability, possible alterations of the redox state of ferredoxin and associated electron carriers, and inhibited enzyme-enzyme or enzyme-substrate interactions involved in the light activation process.Abbreviations and symbols DHAP dihydroxyacetone phosphate - PGA 3-phosphoglycerate - _s osmotic potential     

Paraheliotropic leaf movement in Siratro as a protective mechanism against drought-induced damage to primary photosynthetic reactions: damage by excessive light and heat

Damage to primary photosynthetic reactions by drought, excess light and heat in leaves of Macroptilium atropurpureum Dc. cv. Siratro was assessed by measurements of chlorophyll fluorescence emission kinetics at 77 K (-196°C). Paraheliotropic leaf movement protected waterstressed Siratro leaves from damage by excess light (photoinhibition), by heat, and by the interactive effects of excess light and high leaf temperatures. When the leaves were restrained to a horizontal position, photoinhibition occurred and the degree of photoinhibitory damage increased with the time of exposure to high levels of solar radiation. Severe inhibition was followed by leaf death, but leaves gradually recovered from moderate damage. This drought-induced photoinhibitory damage seemed more closely related to low leaf water potential than to low leaf conductance. Exposure to leaf temperatures above 42°C caused damage to the photosynthetic system even in the dark and leaves died at 48°C. Between 42 and 48°C the degree of heat damage increased with the time of exposure, but recovery from moderate heat damage occurred over several days. The threshold temperature for direct heat damage increased with the growth temperature regime, but was unaffected by water-stress history or by current leaf water status. No direct heat damage occurred below 42°C, but in water-stressed plants photoinhibition increased with increasing leaf temperature in the range 31–42°C and with increasing photon flux density up to full sunglight values. Thus, water stress evidently predisposes the photosynthetic system to photoinhibition and high leaf temperature exacerbates this photoinhibitory damage. It seems probable that, under the climatic conditions where Siratro occurs in nature, but in the absence of paraheliotropic leaf movement, photoinhibitory damage would occur more frequently during drought than would direct heat damage.Abbreviations and symbols PFD photon flux area density - PSI, PSII photosyntem I, II - F _M, F _O, F _V maximum, instantaneous, variable fluorescence emission - PLM paraheliotropic leaf movement; all data of parameter of variation are mean ± standard error     

The effect of plant-hormone pretreatments on ethylene production and synthesis of 1-aminocyclopropane-1-carboxylic acid in water-stressed wheat leaves

Excised wheat (Triticum aestivum L.) leaves, when subjected to drought stress, increased ethylene production as a result of an increased synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) and an increased activity of the ethyleneforming enzyme (EFE), which catalyzes the conversion of ACC to ethylene. The rise in EFE activity was maximal within 2 h after the stress period, while rehydration to relieve water stress reduced EFE activity within 3 h to levels similar to those in nonstressed tissue. Pretreatment of the leaves with benzyladenine or indole-3-acetic acid prior to water stress caused further increase in ethylene production and in endogenous ACC level. Conversely, pretreatment of wheat leaves with abscisic acid reduced ethylene production to levels produced by nonstressed leaves; this reduction in ethylene production was accompanied by a decrease in ACC content. However, none of these hormone pretreatments significantly affected the EFE level in stressed or nonstressed leaves. These data indicate that the plant hormones participate in regulation of water-stress ethylene production primarily by modulating the level of ACC.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - BA N⁶-benzyladenine - EFE ethylene-forming enzyme - IAA indole-3-acetic acid     

Water permeability of Betula periderm

The water permeability of periderm membranes stripped from mature trees of Betula pendula Roth was investigated. The diffusion of water was studied using the system water/membrane/water, and transpiration was measured using the system water/membrane/water vapor. Betula periderm consists of successive periderm layers each made up of about 5 heavily suberized cell layers and a varying number of cell layers that are little suberized, if at all. It is shown that these layers act as resistances in series. The permeability coefficient of the diffusion of water (P _d) can be predicted with 79% accuracy from the reciprocal of the membrane weight (x in mg cm^-2) by means of the linear equation P _d=14.69·10^-7 x-0.73·10^-7. For example, the P _d of a periderm membrane having a weight of 10 mg cm^-2 (approx. 250 m thick) is 7.4·10^-8 cm s^-1, which is comparable to the permeability of cuticles. This comparison shows that on a basis of unit thickness, Betula periderm is quite permeable to water as cuticles have the same resistance with a thickness of only 0.5 to 3 m. It is argued that this comparatively high water permeability of birch periderm is due to the fact that middle lamellae and the primary walls of periderm cells are not at all, or only incompletely suberized and, therefore, form a hydrophilic network within which the water can flow. This conclusion is based on the following observations: (1) Middle lamellae and primary walls stain strongly with toluidine blue, which shows them to be polar. (2) If silver ions are added as tracer for the flow of water, they are found only in the middle lamellae, primary walls, and in plasmodesmata, while no silver can be detected in the suberized walls. (3) Permeability coefficients of transpiration strongly depend on water activity. This shows conclusively that water flows across Betula periderm via a polar pathway. It is further argued that liquid continuity is likely to be maintained under all physiological conditions in the network formed by middle lamellae and primary walls. On the other hand, the lumina of periderm cells, intercellular air spaces in the lenticels, and even the pores in the suberized walls (remainders of plasmodesmata) will drain at a humidity of 95% and below. Due to the presence of intercellulars the permeability coefficient of lenticels is much greater than that of the periderm. A substantial amount of the total water, therefore, flows as vapor through lenticels even though they cover only 3% of the surface.Abbreviations PM perideron membrane - P _d permeability coefficient for diffusion of water - P _tt permeability coefficient of transpiration - MES (N-morpholino)ethane sulfonic acid     

Functional group contributions to the partitioning of phenols between liposomes and water

The temperature dependency of the partitioning of p-alkylphenols and p-halophenols has been determined between dimyristoyl phosphatidylcholine liposomes and 0.15 M NaCl. Partition coefficients increased as a function of temperature below the endothermic phase transition temperature (T_c) of the phospholipid but decreased above this temperature. The transfer process was found to be entropy-dominated below and enthalpy-dominated above the T_c, although large negative entropy changes were observed. Regular changes in the thermodynamic functions, partition coefficients and functional group free energies occurred as a function of the alkyl chain length or size of the halogen substituent below but not above the T_c. This has tentatively been attributed to increased phenol-phospholipid interaction at the higher temperatures. The partitioning of p-fluorophenol behaved in a manner expected of fluorinated compounds, yielding relatively low partition coefficients, but it produced an additional effect of markedly lowering the T_c of dimyristoyl phosphatidylcholine. Good correlations of the partition coefficients in liposomes with those in bulk organic solvents and with molecular size of the solute have been obtained.     

Water potential gradients of tall and short cultivars of winter wheat

Summary Water and osmotic potentials were measured with thermocouple psychrometers, weekly after heading, two times each day at pre-dawn and at noon, in flag leaves and grain of tall and short cultivars of winter wheat grown in the field under rain-fed conditions.Water was held with less tension in the grain than in the leaf for both tall and short cultivars. The tall cultivars had lower leaf water potentials, but higher grain water potentials, than the short cultivars. The grain osmotic potential was lower in the short cultivars compared to the tall ones. Grain yield of short cultivars (1810 kg/ha) was more than that of tall cultivars (1730 kg/ha). Apparently higher leaf water potentials of short cultivars enabled more photosynthates to move into the grain.     

Theoretical investigations on circular and chain-like hydrogen bonded structures found in two crystal forms of α-cyclodextrin hexahydrate: Models for hydration and water clusters

Hydration of macromolecules and the structure of water of crystallization are not understood in detail because in these complex systems. H-atoms cannot be located and the hydrogen bonding schemes are not known. X-ray and neutron diffraction studies on a hydrated oligosaccharide, α-cyclodextrin 6H₂O, ((C₆H₁₀O₅)₆·6H₂O), crystals forms A and B, gave insight into the chain-like and circular arrangement of hydrogen bonds. In the circles, homodromic (unidirectional) and antidromic (counter-running) orientation of five to six hydrogen bounds is observed. PCILO calculations showed that homodromic circles and chains are approx. 8% per hydrogen bond more stable than antidromic circles, that the changes in electronic charges on H and O atoms are greater in homo than in antidromic systems and that the dipole moments are only approx. 3 D in the homodromic circles but 6–8 D in chain-like and antidromic arrangement. These results have been interpreted in terms of cooperative effect. Circular systems are considered as structural elements in hydration shells of macromolecules and in the assembly of ‘flickering’ water clusters.     

The coxal glands of geophilomorpha (chilopoda): Organs of osmoregulation

Summary The organs terminating at the coxal pores of the tug-legs of Geophilomorpha are not repugnatorial glands, but possess typical transport epithelia with deep apical and basal infoldings of the cell membranes, between which numerous large mitochondria are located. Many transport vesicles are found in the basal region but fewer in the apical cytoplasm. The apex is characterized by bundles of longitudinally oriented microtubules, sparse endoplasmic reticulum and free ribosomes. Single neurosecretory axons with synaptoid areas are scattered among the cells. It is suggested that the coxal organs have a diuretic function in moist habitats and an antidiuretic effect in arid environments. The switch-over is evidently controlled by a neuroendocrine mechanism.