Hydrostatic pressure mimics gravitational pressure in characean cells

Summary Hydrostatic pressure applied to one end of a horizontalChara cell induces a polarity of cytoplasmic streaming, thus mimicking the effect of gravity. A positive hydrostatic pressure induces a more rapid streaming away from the applied pressure and a slower streaming toward the applied pressure. In contrast, a negative pressure induces a more rapid streaming toward and a slower streaming away from the applied pressure. Both the hydrostatic pressure-induced and gravity-induced polarity of cytoplasmic streaming respond identically to cell ligation, UV microbeam irradiation, external Ca²⁺ concentrations, osmotic pressure, neutral red, TEA Cl^–, and the Ca²⁺ channel blockers nifedipine and LaCl₃. In addition, hydrostatic pressure applied to the bottom of a vertically-oriented cell can abolish and even reverse the gravity-induced polarity of cytoplasmic streaming. These data indicate that both gravity and hydrostatic pressure act at the same point of the signal transduction chain leading to the induction of a polarity of cytoplasmic streaming and support the hypothesis that characean cells respond to gravity by sensing a gravity-induced pressure differential between the cell ends.     

An assessment of phase transitions in soybean membranes

Phase transitions were measured in vesicles of phospholipids, alone and in various combinations, and in pelleted mitochondrial membranes, using thermal (DSC) and optical methods. The objective was to consider their possible involvement in chilling injury of soybeans (Glycine max [L.] Merr. cv Wayne 1977). Saturated phospholipids showed clear transitions in the temperature range of 50°C to near 0°C. When mixtures of two phospholipids were examined, there was a marked lowering and broadening of the transition peaks, and a shift in the transition temperatures to intermediate temperatures. The unsaturated phospholipids that occur naturally in soybeans showed no detectable phase transitions in this temperature range, alone or in combinations. Examination of the polar lipids from soybean asolectin revealed no transitions in the biological temperature range; the additions of cations such as Ca²⁺ and La³⁺ did not evoke a detectable phase transition in them. Mitochondrial membrane pellets likewise showed no transitions. The application of these two direct methods of examination of membrane components without the addition of foreign agents did not support the suggested occurrence of a bulk phase transition which could be related to chilling injury in soybeans.     

Solute leakage resulting from leaf desiccation

The leakage of solutes from foliar tissue is utilized as a dynamic measure of apparent changes in membrane integrity in response to desiccation. It is found that rehydrating leaf discs of cowpea (Vigna sinensis [L.] Endl.) show increasing leakiness in proportion to the extent of prior desiccation, whereas Selaginella lepidophylla Spring., a resurrection plant, does not. The elevated leakage rate of cowpea after desiccation recovers with time, and the passage of time in the stressed condition results in reduced subsequent leakiness. These characteristics are interpreted as suggesting that the leakage of solute reflects the condition of cellular membranes, and that desiccation stress leads to lesions in the membranes. The kinetics of solute leakage is suggested as a simple means of following changes in membrane lesions and associated features of membrane repair and hardening.     

Respiratory Transition during Seed Germination

Experiments with germinating seeds of Wayne soybean (Glycine max Merr.) show that between the 4th and the 8th hour of germination, respiration experiences a transition from predominantly “alternate” respiration, which is sensitive to salicylhydroxamic acid, to a cyanide-sensitive respiration. The dependence of early germination stages on alternate respiration is reflected in several types of seed functions, including subsequent root growth rate, chlorophyll synthesis, and germination itself. The early period of germination is shown to require a normal O₂ tension, which is no longer a requirement at later stages. The changing sensitivity to cyanide and to salicylhydroxamic acid is found to be common to seven different types of germinating seeds. It is proposed that the alternate pathway of respiration provides something essential for the completion of the earliest stages of seed germination.     

Effects of inorganic solutes on the binding of auxin

The binding of α-naphthaleneacetic acid (¹⁴C-NAA) to pelletable particulates from corn (Zea mays) coleoptiles was found to be influenced by inorganic solutes. La³⁺, Ca²⁺, and Mg²⁺ increased the binding whereas monovalent cations did not. The concentrations of CaCl₂ which increased auxin binding were similar to those which inhibited coleoptile elongation in the presence of auxin. These results are interpreted as suggesting that the alteration of hormonal effectiveness by some inorganic solutes involves alterations in the attachment of the hormone to binding sites in the cell.     

Effects of inorganic salts on tissue permeability

Inorganic solutes are shown to alter the permeability of root and leaf tissues. Experiments with beet root tissues reveal that CaCl(2) decreases leakage of betacyanin from the tissue, that (NH(4))(2)SO(4) increases leakage, and that each salt can relieve the effects of the other. A comparison of cations and anions shows a range of effects with the various solutes. Experiments with Rumex obtusifolius L. leaf discs reveal that whereas CaCl(2) defers the development of senescence, (NH(4))(2)SO(4) hastens senescence and increases the leakage of materials out of the leaf discs. The solute effect on Rumex obtusifolius L. is prevented by gibberellin. CaCl(2) can relieve the (NH(4))(2)SO(4) effect. The results are interpreted as indicating that the inorganic solutes may serve to alter the permeability of membranes through alterations of interactions between water and macromolecules in the tissues; the interpretation is consistent with the evidence for opposite effects of Ca and NH(4), the effective concentrations being about 10(-3)m, and the reversibility of the effects of one solute by another of opposite stabilization-destabilization effect.     

Genetics of house flies. Variability studies with North Dakota, Texas, and Florida populations.

Genetic data were used to compare the structure of native house fly populations collected in North Dakota, Texas, and Florida. Recombination studies with mutant markers on chromosomes 3 and 4 indicated a lack of inversion polymorphism among the three populations in those areas of the genetic map studied. Significant differences were observed among flies from the three regions with regard to the frequency of 1) females that produced only male progeny, and 2) male-determining 3rd chromosomes (IIIm chromosomes). However, the North Dakota and Texas flies were more similar to each other than to the Florida flies since populations from the two former areas possessed a low frequency of both male-producing females and IIIm chromosomes; in contrast, the Florida population was void of females that produced males only and a high percentage if not all Florida males appeared to possess the IIIm male-determining mechanism. Tests for recessive lethal 3rd chromosomes showed that there was no significant difference in the frequency of lethal factors recovered from the North Dakota and Texas flies; the presence of IIIm chromosomes in Florida males precluded the recovery of lethal factors from this population by the method employed. The data suggest that house fly strains to be employed in genetic control programs should 1) originate from target control areas to avoid possible behavioral differences existing among flies from different locales, 2) be initiated with as many flies as possible to provide a background for the maintenance of variability, and 3) be renewed periodically with field-collected material since the genotype may be capable of rapid reorganization in response to laboratory selection pressures.     

Fascioloides magna (Bassi, 1875) in feral swine from southern Texas.

Between 1971 and 1975, Fascioloides magna was found in 46 of 67 (69%) feral swine (Sus scrofa) in southern Texas. Flukes were recovered from swine in areas where F. magna commonly has been recovered from white-tailed deer and cattle. One to 12 flukes were recovered from each infected animal. Their presence was indicated by black hematin pigment on the liver and various other internal organs. Eggs were not detected in the gallbladder or feces of infected animals although mature flukes and eggs were recovered in the livers suggesting that, like cattle, feral swine can be infected but are aberrant hosts for the parasite and do not disseminate eggs.     

Key parameters controlling stiffness variability within trees: a multiscale experimental–numerical approach

Microstructural properties of wood vary considerably within a tree. Knowledge of these properties and a better understanding of their relationship to the macroscopic mechanical performance of wood are crucial to optimize the yield and economic value of forest stocks. This holds particularly for the end-use requirements in engineering applications. In this study the microstructure–stiffness relationships of Scots pine are examined with a focus on the effects of the microstructural variability on the elastic properties of wood at different length scales. For this purpose, we have augmented microstructural data acquired using SilviScan-3? (namely wood density, cell dimensions, earlywood and latewood proportion, microfibril angle) with local measurements of these quantities and of the chemical composition derived from wide-angle X-ray scattering, light microscopy, and thermogravimetric analysis, respectively. The stiffness properties were determined by means of ultrasonic tests at the clear wood scale and by means of nanoindentation at the cell wall scale. In addition, micro-mechanical modeling was applied to assess the causal relations between structural and mechanical properties and to complement the experimental investigations. Typical variability profiles of microstructural and mechanical properties are shown from pith to bark, across a single growth ring and from earlywood to latewood. The clear increase of the longitudinal stiffness as well as the rather constant transverse stiffness from pith to bark could be explained by the variation in microfibril angle and wood density over the entire radial distance. The dependence of local cell wall stiffness on the local microfibril angle was also demonstrated. However, the local properties did not necessarily follow the trends observed at the macroscopic scale and exhibited only a weak relationship with the macroscopic mechanical properties. While the relationship between silvicultural practice and wood microstructure remains to be modeled using statistical techniques, the influence of microstructural properties on the macroscopic mechanical behavior of wood can now be described by a physical model. The knowledge gained by these investigations and the availability of a new micromechanical model, which allows transferring these findings to non-tested material, will be valuable for wood quality assessment and optimization in timber engineering.