Effects of flooding under hydrostatic pressure on the respiratory metabolism of germinated wheat seeds

Germinated wheat seeds ( Triticum aestivum L. cv. Barqai) that had been subjected to short hydrostatic pressure treatments (0.3–1.2 MPa) changed their normal metabolism into one which is characterized by a high ethanol production, a low O₂ consumption and a low CO₂ evolution. Alcoholic fermentation could account for ca half of the CO₂ evolved from the pressurized seeds. The level of acetaldehyde was low, though significantly higher in the pressurized seeds than in the controls. Subjection of wheat seeds to osmotic stress under aerobic conditions lowered their O₂ uptake and CO₂ evolution but did not induce ethanol production. Exposure of pressurized seeds to NaCl stress did not alter their ethanol production beyond that which had been induced by pressure. Ethanol production by pressurized seeds increased following either the addition of sucrose or by excision of the embryos from the endosperms. More electrolytes leaked into the embedding solution from pressurized seeds than from control seeds. Exogenous ethanol was toxic to wheat seeds at concentrations as low as 343 m M . The effects of hydrostatic pressure and of the consequently induced ethanol production on the mortality of flooded seeds is discussed.     

Uptake of Cd2+ and Fe2+ by excised roots of Tamarix aphylla

The uptake of Cd²⁺ by excised roots of Tamarix aphylla (L.) Karst, was investigated using roots of hydroponically grown plants. The concentration isotherm of Cd²⁺ uptake approached saturation with a single phase hyperbola. The time course of Cd²⁺ absorption was generally hyperbolic, with an apparent linear section between 2 and 30 min. The temperature response varied among different temperature ranges: a Q₁₀ of approximately 1.9 was found between 10 and 20°C, but at higher and lower temperatures Q₁₀ values were only 1–1.3. It is concluded that Cd²⁺ uptake by the roots of T. aphylla at moderate temperatures is mediated by a metabolic process, combined with a passive influx component that becomes dominant at higher and lower temperatures. The distribution of the absorption sites for Cd²⁺ and for Fe²⁺ along the roots of T. aphylla was also investigated. Cadmium uptake showed no apparent pattern, whereas a distinct pattern of uptake was observed for Fe²⁺, with the highest rates at the root tip. Iron absorption was stimulated in the presence of nutrients, whereas that of Cd²⁺ was inhibited. Adsorption and absorption of Cd²⁺ were strongly inhibited by Ca²⁺ and by Mg²⁺, but were unaffected by Fe²⁺. Monovalent ions (Na⁺, K⁺, Li⁺) also reduced Cd²⁺ absorption, but to a lesser extent than Ca²⁺ and Mg²⁺. Uptake of Cd⁺ was reduced at lower pH of the medium. The importance of interfering cations for Cd²⁺ tolerance of T. aphylla is emphasized.     

Ultrastructural localization and identification ofAzospirillum brasilense Cd on and within wheat root by immuno-gold labeling

Azospirillum brasilense Cd localization in wheat roots was studied by light microscopy, by scanning, and by transmission electron microscopy.A. brasilense Cd cells were specifically identified immunocytochemically around and within root tissues.A. brasilense Cd cells found both outside and inside inoculated roots were intensively labeled with colloidal gold. In non-axenic cultures other bacterial strains or plant tissue were not labeled, thereby providing a non-interfering background. The roots of axenic grown wheat plants were colonized both externally and internally byA. brasilense Cd after inoculation, whereas non-axenic cultures were colonized by other bacterial strains as well.A. brasilense Cd cells were located on the root surface along the following zones: the root tip, the elongation, and the root-hair zone. However, bacteria were located within the cortex only in the latter two zones. In a number of observations, an electron dense material mediated the binding of bacterial cells to outer surfaces of epidermal cells, or between adjacent bacterial cells.A. brasilense Cd were found in root cortical intercellular spaces, but were not detected in either the endodermal layer or in the vascular system. This study proposes that in addition to root surface colonization,A. brasilense Cd forms intercellular associations within wheat roots.     

Fusion of native Sendai virions with human erythrocytes : Quantitation by fluorescence photobleaching recovery

We have recently developed a method to quantitate the fusion of reconstituted viral envelopes with cells by fluorescence photobleaching recovery (FPR) (Aroeti, B & Henis, Y I, Biochemistry 25 (1986) 4588). The method is based on the incorporation of non quenching concentrations of the fluorescent lipid probe N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)phosphatidylethanolamine during the reconstitution of the viral envelopes (the latter probe does not incorporate efficiently into the membrane of native virions). In the present work, we employed the fluorescent dye octadecyl rhodamine B chloride (R18), which can be incorporated directly into the membrane of native enveloped virions, to extend the FPR method to study fusion between native Sendai virions and intact human erythrocytes. The R18 fluorescence was found to be quenched in the viral envelope at the concentration range required for the FPR experiments, possibly due to preferential insertion of the probe into specific domains in the viral membrane. We therefore developed a correction (presented in the Appendix) which takes into account the lower quantum yield of the probe molecules in the membranes of unfused virions in the calculation of the fraction of fused virions from the FPR experiments. The results demonstrate that the method does indeed measure virus-cell fusion, and that the contribution of exchange to the measurements is not significant. The applicability of the method was further verified by the similarity of the results to those obtained independently by fluorescence dequenching measurements, and its ability to measure the distribution of virus-cell fusion within the cell population was demonstrated. These results suggest that the use of R18 can enlarge the scope of the FPR experiments to study the fusion of native virions with cells.     

Alginate Beads as Synthetic Inoculant Carriers for Slow Release of Bacteria That Affect Plant Growth

Uniform synthetic beads were developed as carriers for the bacterial inoculation of plants. The beads are made of sodium alginate and skim milk and contain a large reservoir of bacterial culture which releases the bacteria at a slow and constant rate. The beads are biodegradable and produce no environmental pollution. The strength of the beads, the rate of bacterial release, and the time of their survival in the soil can be controlled by several hardening treatments. The final product, lyophilized beads, is simple to use and is applied to the seeds concomitantly with sowing. The released bacteria are available for root colonization immediately at seed germination. Dry beads containing bacteria can be stored at ambient temperature over a long period without loss of bacterial content; storage requires a limited space, and the quality control of a number of bacteria in the bead is simple. The level of plant inoculation with beads was similar to that with previously used peat inoculants, but the former method yielded more consistent results, as the frequency of inoculated plants was much higher. The former method provides a different approach for inoculation of plants with beneficial rhizosphere bacteria.     

Inhibition of Seed Germination and Root Development Caused by Xanthomonas campestris pv. vesicatoria in Pepper and Tomato

Inoculation of pepper seeds with the leaf pathogen Xanthomonas campestris pv. vesicatoria inhibited pepper germination. The inhibitory effect, which was stronger in non-sterilized light textured soils, decreased with time, and after 20, days or more, there was no difference between inoculated and non-inoculated seeds. Inhibitory substance(s) within the cytoplasmatic fraction of pathogen cells inhibited the germination of non-host tomato seeds. No relationship between pathogenicity to pepper leaves and inhibition of pepper seed germination was detected. The inhibitory substance(s) was found in two out of four X. campestris pv. vesicatoria strains. Heat-killed bacteria suppressed growth of pepper but not tomato seedlings. It is, therefore, suggested that the inhibition of seed germination and the decrease in root development are different modes of X. campestris pv. vesicatoria pathogenesis toward pepper plants.     

The interrelations between high- and low-molecular-weight forms of normal and mutant (Krabbe-disease) galactocerebrosidase

Galactocerebrosidase (β-d-galactosyl-N-acylsphingosine galactohydrolase; EC 3.2.1.46) activity of brain and liver preparations from normal individuals and patients with Krabbe disease (globoid-cell leukodystrophy) have been separated by gel filtration into four different molecular-weight forms. The apparent mol.wts. were 760000±34000 and 121000±10000 for the high- and low-molecular-weight forms (peaks I and IV respectively) and 499000±22000 (mean±s.d.) and 256000±12000 for the intermediate forms (peaks II and III respectively). On examination by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the high- and low-molecular-weight forms revealed a single protein band with a similar mobility corresponding to a mol.wt. of about 125000. Antigenic identity was demonstrated between the various molecular-weight forms of the normal and the mutant galactocerebrosidases by using antisera against either the high- or the low-molecular-weight enzymes. The high-molecular-weight form of galactocerebrosidase was found to possess higher specific activity toward natural substrates when compared with the low-molecular-weight form. It is suggested that the high-molecular-weight enzyme is the active form in vivo and an aggregation process that proceeds from a monomer (mol.wt. approx. 125000) to a dimer (mol.wt. approx. 250000) and from the dimer to either a tetramer (mol.wt. approx. 500000) or a hexamer (mol.wt. approx. 750000) takes place in normal as well as in Krabbe-disease tissues.