Salt‐resistant and salt‐sensitive wheat genotypes show similar biochemical reaction at protein level in the first phase of salt stress

Salinity has a two‐phase effect on plant growth, an osmotic effect due to salts in the outside solution and ion toxicity in a second phase due to salt build‐up in transpiring leaves. To elucidate salt‐resistance mechanisms in the first phase of salt stress, we studied the biochemical reaction of salt‐resistant and salt‐sensitive wheat (Triticum aestivum L.) genotypes at protein level after 10 d exposure to 125 mM–NaCl salinity (first phase of salt stress) and the variation of salt resistance among the genotypes after 30 d exposure to 125 mM–NaCl salinity (second phase of salt stress) in solution culture experiments in a growth chamber. The three genotypes differed significantly in absolute and relative shoot and root dry weights after 30 d exposure to NaCl salinity. SARC‐1 produced the maximum and 7‐Cerros the minimum shoot dry weights under salinity relative to control. A highly significant negative correlation (r² = –0.99) was observed between salt resistance (% shoot dry weight under salinity relative to control) and shoot Na⁺ concentration of the wheat genotypes studied. However, the salt‐resistant and salt‐sensitive genotypes showed a similar biochemical reaction at the level of proteins after 10 d exposure to 125 mM NaCl. In both genotypes, the expression of more than 50% proteins was changed, but the difference between the genotypes in various categories of protein change (up‐regulated, down‐regulated, disappeared, and new‐appeared) was only 1%–8%. It is concluded that the initial biochemical reaction to salinity at protein level in wheat is an unspecific response and not a specific adaptation to salinity.     

Proton release by N2‐fixing plant roots: A possible contribution to phytoremediation of calcareous sodic soils

With a world‐wide occurrence on about 560 million hectares, sodic soils are characterized by the occurrence of excess sodium (Na⁺) to levels that can adversely affect crop growth and yield. Amelioration of such soils needs a source of calcium (Ca²⁺) to replace excess Na⁺ from the cation exchange sites. In addition, adequate levels of Ca²⁺ in ameliorated soils play a vital role in improving the structural and functional integrity of plant cell walls and membranes. As a low‐cost and environmentally feasible strategy, phytoremediation of sodic soils — a plant‐based amelioration — has gained increasing interest among scientists and farmers in recent years. Enhanced CO₂ partial pressure (P_CO2) in the root zone is considered as the principal mechanism contributing to phytoremediation of sodic soils. Aqueous CO₂ produces protons (H⁺) and bicarbonate (HCO₃^‐). In a subsequent reaction, H⁺ reacts with native soil calcite (CaCO₃) to provide Ca²⁺ for Na⁺ Ca²⁺ exchange at the cation exchange sites. Another source of H⁺ may occur in such soils if cropped with N₂‐fixing plant species because plants capable of fixing N₂ release H⁺ in the root zone. In a lysimeter experiment on a calcareous sodic soil (pH_s = 7.4, electrical conductivity of soil saturated paste extract (EC_e) = 3.1 dS m^‐1, sodium adsorption ratio (SAR) = 28.4, exchangeable sodium percentage (ESP) = 27.6, CaCO₃ = 50 g kg^‐1), we investigated the phytoremediation ability of alfalfa (Medicago sativa L.). There were two cropped treatments: Alfalfa relying on N₂ fixation and alfalfa receiving NH₄NO₃ as mineral N source, respectively. Other treatments were non‐cropped, including a control (without an amendment or crop), and soil application of gypsum or sulfuric acid. After two months of cropping, all lysimeters were leached by maintaining a water content at 130% waterholding capacity of the soil after every 24±1 h. The treatment efficiency for Na⁺ removal in drainage water was in the order: sulfuric acid > gypsum = N₂‐fixing alfalfa > NH4NO3‐fed alfalfa > control. Both the alfalfa treatments produced statistically similar root and shoot biomass. We attribute better Na+ removal by the N₂‐fixing alfalfa treatment to an additional source of H⁺ in the rhizosphere, which helped to dissolve additional CaCO₃ and soil sodicity amelioration.     

Mixing of different mineral soil layers by endogeic earthworms affects carbon and nitrogen mineralization

The effect of the endogeic earthworm species Octolasion tyrtaeum (Savigny) on decomposition of uniformly ¹⁴C-labelled lignin (lignocellulose) was studied in microcosms with upper mineral soil (Ah-horizon) from two forests on limestone, representing different stages of succession, a beech- and an ash-tree-dominated forest. Microcosms with and without lower mineral soil (Bw-horizon) were set-up; one O. tyrtaeum was added to half of them. It was hypothesised that endogeic earthworms stabilise lignin and the organic matter of the upper mineral soil by mixing with lower mineral soil of low C content. Cumulative C mineralization was increased by earthworms and by the addition of lower mineral soil. Effects of the lower mineral soil were more pronounced in the beech than in the ash forest. Cumulative mineralization of lignin was strongly increased by earthworms, but only in the beech soil (+24.6%). Earthworms predominantly colonized the upper mineral soil; mixing of the upper and lower mineral soils was low. The presence of lower mineral soil did not reduce the rates of decomposition of organic matter and lignin; however, the earthworm-mediated increase in mineralization was less pronounced in treatments with (+8.6%) than in those without (+14.1%) lower mineral soil. These results indicate that the mixing of organic matter with C-unsaturated lower mineral soil by endogeic earthworms reduced microbial decomposition of organic matter in earthworm casts.     

Nitrate and ammonium nutrition of plants: Effects on acid/base balance and adaptation of root cell plasmalemma H+ ATPase

The increase of rhizosphere pH in the course of nitrate nutrition results from H⁺ consumption in the external medium during uptake of NO₃^? in a H⁺ co-transport and from internal OH^? production during nitrate reduction. Synthesis of organic acids for NH₄⁺ assimilation as well as strong partial depolarization of membrane potential with NH₄⁺ uptake are the important reasons for rhizosphere acidification during ammonium nutrition. Despite differences in proton balance depending on N form, cytoplasmic pH changes are small due to physico-chemical buffering, biochemical pH regulation, H⁺ inclusion in vacuoles, and H⁺ release into the rhizosphere. Because of the large capacity for proton excretion the plasmalemma H⁺ ATPase of root cells plays an essential role during ammonium nutrition. An increase of the kinetic parameter V_max after ammonium nutrition relative to nitrate nutrition suggests that the capacity of H⁺ release may be adjusted to the particular requirements of ammonium nutrition. Moreover, H⁺ ATPase is adjusted not only quantitatively but also qualitatively. The increase of the kinetic parameter k_m as well as the capability of the plasmalemma vesicles in vitro to establish a steeper pH gradient favours the supposition that H⁺ ATPase isoforms are formed which allow H⁺ release into the rhizosphere under conditions of low pH or poor H⁺ buffering of the soil. In this respect species differences exist, e.g. between maize (efficient adaptation) and faba bean (poor adaptation).     

Atmospheric Lead Deposition from 12,400 to ca. 2,000 yrs BP in a Peat Bog Profile,Jura Mountains,Switzerland

The bog at Etang de la Gruère (Jura Mountains, Switzerland) consists of 420 cm of Sphagnum-dominated bog peat overlying 230 cm of Carex-dominated fen peat. One hundred cm below the bog surface, there is a pronounced peak in lead (Pb) concentration (approx. 10 µg/g) which has been dated at 2110 ± 30 BP and can be attributed to Roman Pb mining and smelting. Lead concentrations in peats from deeper, much older layers were measured using ICP-MS and found to be low and relatively constant (0.28 ± 0.04 µg/g, n = 17) from 405 cm to 235 cm which corresponds to the period from approx. 8,000 and 5,500 years before present (BP). In this same interval, scandium (Sc) concentrations (measured using INAA) were 0.07 ± 0.02 µg/g, yielding an average Pb/Sc ratio of 4.1 ± 1.2. These values are assumed to represent the true "background" Pb and Sc concentrations and Pb/Sc ratios of pre-anthropogenic aerosols. At 205 cm the Pb concentrations began to increase by 2 to 3 times, but these are proportional to the increases in aluminum (Al), titanium (Ti), silicon (Si), and Sc, and reflect an increase in Pb deposition supplied by silicate-derived soil dust. This depth, dated at 5,230 BP, coincides with the development of agriculture and indicates the impact of soil cultivation on metal fluxes to the air. At 115 cm, however, the Pb concentrations increase out of proportion with Sc; this point was dated at 3,000 BP and reflects the beginning of Pb contamination by mining and metallurgy in Europe and the Middle East. There are two pronounced peaks in Pb concentrations centered at 435 cm and 555 cm, corresponding with local maxima in ash and ash-forming major elements at the same depths. These samples have been dated at 8,230 BP and 10,590 BP, respectively, indicating the Vasset/Killian volcanic events (Massif Central, France) and Younger-Dryas cold phase as the most likely explanations.     

Relationship of lactation energy intake and occurrence of postweaning estrus to body and backfat composition in sows

Forty-five crossbred primiparous sows were used to determine the relationship of lactation energy intake and the occurrence of postweaning estrus to (1) body fat (percentage), (2) lean body mass (LBM) and (3) qualitative and quantitative characteristics of adipose tissue. Sows received 8 (Lo) or 16 (Hi) Mcal of metabolizable energy (ME)/d during lactation and 5.4 Mcal of ME/d postweaning. Serum samples were obtained 1 d before weaning (d 0) and analyzed for creatinine and urea-N (indices of muscle and amino acid catabolism, respectively). Subcutaneous adipose tissue samples were obtained and analyzed for total lipid and myristic, palmitic, palmitoleic, stearic, oleic and linoleic acids. Last rib backfat thickness determined at weaning was used to estimate body fat (percentage). Lean body mass was estimated from 48-h creatinine excretion rates determined on d 15 and 16 postweaning. Sows fed the Lo diet that returned (Lo-R) and did not return (Lo-NR) to estrus by d 14 postweaning lost more (P less than .01) weight during lactation, gained more (P less than .01) weight postweaning, had higher (P less than .07) body fat (percentage) and a slight trend toward lower creatinine excretion rate than sows fed the Hi diet that returned to estrus (Hi-R). Adipose tissue from sows in the Lo-R and Lo-NR groups had less (P less than .05) lipid than that from sows in the Hi-R group. Concentrations of oleic and stearic acids were lower and higher (P less than .01), respectively, in adipose tissue from sows in the Lo-R and Lo-NR vs Hi-R groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution of Live and Dead Spermatozoa in the Genital Tract of Gilts at Different Times After Insemination

Twenty-four gilts were inseminated pair-wise with live or dead spermatozoa from the same ejaculate. The insemination dose was 100 ml undiluted semen containing, on average, 19×10⁹ spermatozoa. The gilts were slaughtered 1, 2, 6 and 12 h after insemination. The numbers of spermatozoa were counted in the uterus, uterotubal junction and in four equally long segments of the oviduct, called I–IV, with a haemocytometer. IV was adjacent to the uterotubal junction. The numbers of spermatozoa recovered in the uterus diminished significantly during the first 12 h after insemination. From gilts inseminated with live spermatozoa more spermatozoa were recovered in the uterotubal junction than from gilts inseminated with dead spermatozoa. Two h after insemination spermatozoa were recovered in all oviducts. Significantly more live than dead spermatozoa were recovered in Segments III and IV of the oviduct, regardless of time. In gilts inseminated with live spermatozoa the sperm count in Segment I varied significantly with time, being hiigest 2 h after insemination. At 6 and 12 h there were no distinct differences in the distribution of live spermatozoa between the various oviduct segments. The numbers of spermatozoa recovered in the oviduct were at these times apparently related to the sperm depots in the uterotubal junction.