Leaf responses to soil water deficits: Comparative sensitivity of leaf expansion rate and leaf conductance in field-grown sunflower (Helianthus annuus L.)

The relative importance of changes in leaf expansion rate (LER) and leaf conductance (g₁) in the control of crop transpiration depends primarily on their sensitivity to soil water deficits. The aim of this paper was to quantify the responses of LER and g₁ to soil water deficits in sunflower (Helianthus annuus L.) under conditions of moderate (spring) and high (summer) evaporative demand. Soil water content, g₁, and LER were measured in dryland (DRY) and daily-irrigated (WET) crops established on a deep sandy-loam (Typic Xerofluvent) in a Mediterranean environment. There was no difference between g₁ of DRY and WET plants (p>0.20) in contrast with a highly significant difference in LER (p<0.001). Even under the harsh conditions of the summer experiment, g₁ did not respond to water deficit in a ten-day period in which LER of DRY plants was reduced to approx. 30% of that measured in WET controls. This field study indicates that g₁ plays at most a minor role in the control of sunflower transpiration in the pre-anthesis period and confirms the importance of leaf expansion in the regulation of gas exchange of expanding canopies subjected to soil water deficits.     

Nitrogen losses in puddled soils as affected by timing of water deficit and nitrogen fertilization

Erratic rainfall in rainfed lowlands and inadequate water supply in irrigated lowlands can results in alternate soil drying and flooding during a rice (Oryza sativa L.) cropping period. Effects of alternate soil drying and flooding on N loss by nitrification-denitrification have been inconsistent in previous field research. To determine the effects of water deficit and urea timing on soil NO₃ and NH₄, floodwater NO₃, and N loss from added ¹⁵N-labeled urea, a field experiment was conducted for 2 yr on an Andaqueptic Haplaquoll in the Philippines. Water regimes were continuously flooded, not irrigated from 15 to 35 d after transplanting (DT), or not irrigated from 41 to 63 DT. The nitrogen treatments in factorial combination with water regimes were no applied N and 80 kg urea-N ha^–1, either applied half basally and half at 37 DT or half at 11 DT and half at 65 DT. Water deficit at 15 to 35 DT and 41 to 63 DT, compared with continuous soil flooding, significantly reduced extractable NH₄ in the top 30-cm soil layer and resulted in significant but small (<1.0 kg N ha^–1) soil NO₃ accumulations. Soil NO₃, which accumulated during the water deficit, rapidly disappeared after reflooding. Water deficit at 15 to 35 DT, unlike that at 41 to 63 DT, increased the gaseous loss of added urea N as determined from unrecovered ¹⁵N in ¹⁵N balances. The results indicate that application of urea to young rice in saturated or flooded soil results in large, rapid losses of N (mean = 35% of applied N), presumably by NH₃ volatilization. Subsequent soil drying and flooding during the vegetative growth phase can result in additional N loss (mean = 14% of applied N), presumably by nitrification-denitrification. This additional N loss due to soil drying and flooding decreases with increasing crop age, apparently because of increased competition by rice with soil microorganisms for NH₄ and NO₃.     

Fourier transform infrared spectroscopic study of ion binding and intramolecular interactions in the polar head of digalactosyldiacylglycerol

Lipid bilayers composed of digalactosyldiacyl-glycerol (DGDG), that is, Galp1-6Galp1-3DAG, a non-ionic lipid of the thylakoid membrane of chloroplasts, aggregate in aqueous media containing mono- and divalent cations in amounts above a threshold concentration (C_t) of about 1.0, 4.7 and 10.0 mM for Ca²⁺, Mg²⁺ and Na⁺, respectively. In this work, we found that above C_t the DGDG membranes do not undergo fusion and that the aggregation can be reversed, or disrupted. This means that the perturbation induced by the salts results from adsorption, or complexation of the ions in the polar head of DGDG. To investigate this question, we used Fourier transform infrared (FTIR) spectroscopy to identify the molecular sites in DGDG which are modified by interaction, or adduct formation with CaCl₂, MgCl₂ and NaCl. We also determined whether the ions affect the intramolecular hydrogen bonding between the sn₂ ester C = O and the carbon-6 of the -anomer of galactose (Gal). The major conclusions are: (i) the salts do not affect, at least directly, the, ester carbonyl region of DGDG, (ii) the most probable sites of binding, or adsorption, for the ions are the ring oxygen, and (iii) the ring hydroxyls are the sites of either ion complexation or intra- and intermolecular H-bonding in interacting DGDG membranes. Within this framework, the complexation of the ions with Gal might induce total or partial dehydration of the galactolipid headgroup and thus provides the means to overcome the repulsive hydration forces that hinder aggregation of the DGDG membranes.Abbreviations DGDG digalactosyldiacylglycerol - EDTA ethylenediaminetetracetic acid - FTIR Fourier transform infrared - Gal galactose - GIDG D-glucosyldiacylglycerol - Glyc glycerol - LHCII chloroplast light harvesting complex II - MGDG monogalactosyldiacylglycerol - PC phosphatidylcholine - PG phosphatidylglycerol - PS phosphatidylserine - SQDG sulfoquinovosyl-diacylglycerol Correspondence to: M. Fragata     

Magic angle spinning 13C-NMR spin-lattice relaxation study of the location and effects of α-tocopherol,ubiquinone-10 and ubiquinol-10 in unsonicated model membranes

-Tocopherol, ubiquinone-10 and ubiquinol-10 have been studied by high resolution magic angle samples spinning ¹³C-nuclear magnetic resonance in egg yolk phosphatidylcholine multilamellar vesicles model membranes in order to assess their location and the induced perturbations on this model system. -Tocopherol is placed in such a position that it is in close contact with the head group of the phospholipid and exposed to the solvent. In this position it significantly perturbs the phospholipid head group, the 5a-CH₃ and the 7a-CH₃ groups being the closest parts to the membrane surface. On the other hand, ubiquinol-10 perturbs the membrane surface more than ubiquinone-10, but neither compound significantly changed the phospholipid head group conformation.     

Special features of phosphatidylcholine vesicles as seen in cryo-transmission electron microscopy

Vesicles of egg yolk phosphatidylcholine (EYPC) were studied by cryo-transmission electron microscopy. The electron micrographs indicate that, despite the rapidity of cooling, membrane undulations are flattened and some vesicles change their shapes before the samples freeze. These artefacts are attributed to the action of the lateral tension that results from the membrane area contraction associated with the temperature drop. Other micrographs represent grainy membranes and angular vesicles. We regard them as the first direct evidence for the superstructure and optically invisible roughness which were recently postulated for these membranes.     

Haploid production in durum wheat by the interaction of Aegilops kotschyi cytoplasm and 1BL/1RS chromosomal interchange

The present study describes the development of an alloplasmic haploid-inducer in durum wheat cv Cando. This cultivar possesses the homozygous wheat-rye translocation 1BL/1RS from the 6x-wheat cv Veery. The nucleus of 4x-Cando-Veery 1BL/1RS was introduced into Aegilops kotschyi cytoplasm by initially using (kotschyi)-Salmon as the maternal parent. In the cross of this alloplasmic durum line with Cando-Veery 1BL/1RS, which was used as the recurrent pollen parent, haploids (n=14) were produced. The frequency of haploids increased from 5.7% in the F₁ generation to 14% in the BC₁ generation. The presence of rye chromosome arm 1RS and the concomitant loss of 1BS in (kotschyi)-Cando-Veery 1BL/1RS are necessary for haploid induction. Proposals are made which may enable the use of haploids produced by nucleo-cytoplasmic interactions in future wheat breeding programs.     

Wave-separation in complex systems. Application to brain-signals

A departure from single-system dynamics, that may arise in characterizing self-organized dynamics of complex systems, is dealt with by using the Karhunen-Loève expansion of the trajectory matrix to decompose an experimental signal in a sum of spectral features. For an electroencephalographic -signal, a separation of waves and extraction of additive sub-signals are achieved, each sub-signal covering a well-bounded and physiologically meaningful frequency range. From the subsignals, an attractor that vanishes on phase-randomizing the data is characterized, under conditions where none was found for the recorded signal.     

Dynamics of the immune system response in cerebrospinal fluid and blood of SIVmac-infected rhesus monkeys

Paired sera and CSF samples were collected from SIV_mac-infected macaques. Animals infected with SIV_mac251 maintained low gag and high env-specific antibody levels in plasma. Increasing env-specific antibody titers in CSF were associated in one animal with strong intrathecal synthesis. SIV_mac239-infected monkeys revealed high antibody titers of gag and env-specificity, in one animal accompanied by weak intrathecal synthesis of virus-specific antibodies. In all animals, the CD4/CD8 ratio in CSF decreased faster compared to blood.     

NMR imaging of root water distribution in intact Vicia faba L plants in elevated atmospheric CO2

The effect of elevated atmospheric CO₂ on water distribution in the intact roots of Vicia faba L. bean seedlings grown in natural soil was studied noninvasively with proton (¹H) nuclear magnetic resonance (NMR) imaging. Exposure of 24-d-old plants to atmospheric CO₂-enriched air at 650 cm³ m^?3 produced significant increases in water imaged in upper roots, hypogeal cotyledons and lower stems in response to a short-term drying-stress cycle. Above ground, drying produced negligible stem shrinkage and stomatal resistance was unchanged. In contrast, the same drying cycle caused significant depletion of water imaged in the same upper root structures in control plants subject to ambient CO₂ (350 m³ m^?3), and stem shrinkage and increased stomatal resistance. The results suggest that inhibition of transpiration caused by elevated CO₂ does not necessarily result in attenuation of water transport from lower root structures. Inhibition of water loss from upper roots and lower stem in elevated CO₂ environments may be a mitigating factor in assessing deleterious effects of greenhouse changes on crops during periods of dry climate.     

Transport across the bacterial outer membrane

Diffusion of small molecules across the outer membrane of gram-negative bacteria may occur through protein channels and through lipid bilayer domains. Among protein channels, many examples of trimeric porins, which produce water-filled diffusion channels, are known. Although the channels are nonspecific, the diffusion rates of solutes are often drastically affected by their gross physicochemical properties, such as size, charge, or lipophilicity, because the channel has a dimension not too different from that of the diffusing solutes. In the last few years, the structures of three such porins have been solved by X-ray crystallography. It is now known that a monomer unit traverses the membrane 16 times as -strands, and one of the external loop folds back into the channel to produce a narrow constriction. Most of the static properties of the channel, such as the pore size and the position of the amino acids that produce the constriction, can now be explained by the three-dimensional structure. Controversy, however, still surrounds the issue of whether there are dynamic modulation of the channel properties in response to pH, ionic strength, or membrane potential, and of whether such responses are physiological. More recently, two examples of monomeric porins have been identified. These porins allow a very slow diffusion of solutes, but the reason for this low permeability is still unclear. Finally, channels with specific binding sites facilitate the diffusion of specific classes of nutrients, often those compounds that are too large to penetrate rapidly through the porin channels. Lipid bilayers in the outer membrane were shown to be perhaps 50- to 100-fold less permeable to uncharged, lipophilic molecules in comparison with the bilayers made of the usual glycerophospholipids. This is caused by the presence of a lipopolysaccharide leaflet in the bilayer, and more specifically, by the presence of a larger number of fatty acids in each lipid molecule, and by the absence of unsaturated fatty acids in the lipopolysaccharide structure.