Root exudation and physiological status of a root-colonizing fluorescent pseudomonad in mycorrhizal and non-mycorrhizal pepper (Capsicum annuum L.)

Ultramafic (serpentine) soils from and adjacent to the Dun Mountain Ophiolitic Belt, South Island, New Zealand were analysed for 11 elements in order to establish to what degree edaphic factors influenced the character of the overlying vegetation. Using principal components analysis with a mutual plot of the first two principal components, involving the total elemental concentrations in the soils, it was possible to divide the soils into 6 virtually non-overlapping fields, each of which represented a specific vegetation community. Component 1 was essentially an ultramafic plot with heavy loadings from the elements chromium, cobalt, iron, magnesium, manganese, and nickel. Component 2 was a non ultramafic plot with heavy loadings from aluminium, copper and zinc. For elements extracted from the soils at pH 5.9, discrimination was somewhat poorer but confirmed the great importance of magnesium and nickel as controlling elements for the serpentine vegetation. It was concluded that the results indicated the overriding importance of edaphic factors in controlling the serpentine vegetation.     

Root Distribution and Nutrient Status of Mycorrhizal and Non-mycorrhizal Pinus sylvestris L. Seedlings Growing in a Sandy Substrate with Lignite Fragments

Reclaimed mine soils of the Lusatian mining district are characterised by small-scale heterogeneous distribution of lignite fragments of varying size embedded in a matrix of Tertiary and Quaternary sandy material. Despite amelioration with basic fly ashes, ongoing pyrite oxidation and the subsequent acidification generate a high physical and chemical heterogeneity within the substrate, which could negatively affect root proliferation. We hypothesised that this limitation for the root system may be compensated for by intensive exploration of the porous lignite fragments by roots and/or mycorrhizal hyphae to access water and nutrients stored in these fragments. To test this hypothesis, we compared growth, shoot nutrient content, and root distribution of mycorrhizal and non-mycorrhizal Pinus sylvestris L. seedlings in lignite-containing and lignite-free sandy substrate. Rhizotrons used for this experiment were filled with a sandy matrix with 6–9 evenly distributed spots of lignite fragments. Treatments included different levels of water and nutrient availability. After 8 months of growth, root tip vitality as well as growth and shoot nutrient concentration of the plants was higher for treatments with lignite spots in the sandy substrate than for sandy substrate without such amendments. Compared to the non-mycorrhizal plants, the seedlings inoculated with Paxillus involutus (Batsch) Fr. had a higher root dry mass, an increased number of root tips and a higher root length. These results confirm our hypothesis that the lignite fragments are an important nutrient and water reservoir for plants in these mine soils and they indicate that mycorrhizal colonisation may allow an intensive exploration of porous lignite fragments by mycorrhizal hyphae.     

Effects of salinity on microbial tolerance to drying and rewetting

Soil salinity and fluctuations in soil matric potential are stressors for soil microorganisms which, in turn, may affect soil organic matter turnover. In response to salinity and low soil water content, many microorganisms accumulate osmolytes. Therefore, it is conceivable that microorganisms in saline soils are more tolerant to drying and rewetting (DRW) stress than those in non-saline soils. An experiment was carried out with three different salinity levels: electrical conductivity (EC_1:5) 0, 2 and 4 dS m^?1 (EC0, EC2, EC4), and two water treatments: a constantly moist control or two DRW cycles. Respiration as an indicator of microbial activity was measured throughout the 59 days of incubation. At the end of the second dry period (day 35) and at the end of the following moist incubation (day 59), microbial biomass and microbial community structure were determined by phospholipid fatty acid (PLFA) analysis. Increasing salinity decreased microbial activity but did not affect its resistance to DRW. On day 59, cumulative respiration decreased in the order EC0 > EC2 > EC4 with no differences between water treatments. Fungal biomass was negatively affected by salinity at the end of the experiment, while bacterial biomass was unaffected. Microbial community structure in moist treatments differed between salinity levels, with EC4 influencing microbial community structure earlier than EC2. The resistance of microbial communities to DRW stress was salt level dependent; only beyond a critical salinity level adaptation to salt stress was able to reduce the impact of water stress on microbial community structure.     

Attachment and detachment of bacteria on surfaces with tunable and switchable wettability

Controlling accumulations of unwanted biofilms requires an understanding of the mechanisms that organisms use to interact with submerged substrata. While the substratum properties influencing biofilm formation are well studied, those that may lead to cellular or biofilm detachment are not. Surface-grafted stimuli-responsive polymers, such as poly (N-isopropylacrylamide) (PNIPAAm) release attached cells upon induction of environmentally-triggered phase changes. Altering the physicochemical characteristics of such polymeric systems for systematically studying release, however, can alter the phase transition. The physico-chemical changes of thin films of PNIPAAm grafted from initiator-modified self-assembled monolayers (SAMs) of ω-substituted alkanethiolates on gold can be altered by changing the composition of the underlying SAM, without affecting the overlying polymer. This work demonstrates that the ability to tune such changes in substratum physico-chemistry allows systematic study of attachment and release of bacteria over a large range of water contact angles. Such surfaces show great promise for studying a variety of interactions at the biointerface. Understanding of the source of this tunability will require further studies into the heterogeneity of such films and further investigation of interactions beyond those of water wettability.     

Potassium Loss and Changes in the Fine Structure of Corn Root Tips Induced by H-ion

The effects of H, Ca, and anaerobiosis upon loss of K to ambient solutions, upon changes in the fine structure, and upon the respiration of corn root tissue were studied. In the pH range 5.5 to 8.0 losses of K decreased with decreasing H concentration. Ca reduced K loss greatly in the lower part of the pH range but with increasing pH the effect of Ca declined. Losses of K under N₂ were much greater than those measured under air but the same effects of H and Ca were found. The effect of phosphate upon K loss was found to depend upon pH, temperature and the state of development of the tissue.     

Subtype-selectivity of metal-dependent methionine aminopeptidase inhibitors

Inhibitors of methionine aminopeptidases (MetAPs) are treatment options for various pathological conditions. Several inhibitor classes have been described previously, but only few data on the subtype selectivity, which is of crucial importance for these enzymes, is available. We present a systematic study on the subtype- and species-selectivity of MetAP inhibitors that require the binding of an auxiliary metal ion. This includes, in particular, compounds based on the benzimidazole pharmacophore, but also hydroxyquinoline and picolinic acid derivatives. Our data indicates that a significant degree of selectivity can be attained with metal-dependent MetAP inhibitors.     

Fast-twitch skeletal muscles of dystrophic mouse pups are resistant to injury from acute mechanical stress

Loss of the dystrophin-glycoproteincomplex from muscle sarcolemma in Duchenne's muscular dystrophy (DMD)renders the membrane susceptible to mechanical injury, leaky toCa²⁺, and disrupts signaling, but the precise mechanism(s)leading to the onset of DMD remain unclear. To assess the role ofmechanical injury in the onset of DMD, extensor digitorum longus (EDL)muscles from C57 (control), mdx, andmdx-utrophin-deficient [mdx:utrn(/); dystrophic] pups aged 9-12 days were subjected to an acutestretch-injury or no-stretch protocol in vitro. Before the stretches,isometric stress was attenuated for mdx:utrn(/) comparedwith control muscles at all stimulation frequencies (P < 0.05). During the stretches, EDL muscles for each genotypedemonstrated similar mean stiffness values. After the stretches,isometric stress during a tetanus was decreased significantly for bothmdx and mdx:utrn(/) muscles compared withcontrol muscles (P < 0.05). Membrane injury assessedby uptake of procion orange dye was greater for dystrophic comparedwith control EDL (P < 0.05), but, within eachgenotype, the percentage of total cells taking up dye was not different for the no-stretch vs. stretch condition. These data suggest that thesarcolemma of maturing dystrophic EDL muscles are resistant to acutemechanical injury.

     

Survival of Theileria parva-infected adult Rhipicephalus appendiculatus under laboratory and quasi-natural conditions

Adult Rhipicephalus appendiculatus Muguga, having high or low intensities of Theileria parva Muguga infection in their salivary glands, were exposed to 20 °C and 85% relative humidity in the laboratory or quasi-natural conditions. Survival of the ticks and T. parva infections in their salivary glands was then monitored over a two year period. Ticks, having an average infection level of 2 infected acini per female, survived for up to 70 or 106 weeks after moulting under the laboratory or quasi-natural conditions respectively. Those having an infection level of 26 infected acini per female, survived for a similar duration except that those under quasi-natural conditions survived for a slightly shorter duration (102 weeks). Similarly, T. parva parasites survived for much longer periods under quasi-natural conditions than under the laboratory conditions. They survived for up to 38 or 78 weeks post salivary gland infection under the laboratory or quasi-natural conditions respectively in both categories of infection levels. There was apparently a density dependent relationship in T. parva survival, with a dramatic fall in infection occurring in ticks with high levels of infection between weeks 10 and 18 or weeks 38 and 46 post salivary gland infection in those exposed to laboratory or quasi-natural conditions before levelling off. This revised version was published online in July 2006 with corrections to the Cover Date.     

Unique Characteristics of Pb in Soil Contaminated by Red Lead Anti-Corrosion Paint

Red lead (Pb₃O₄) has been extensively used in the past in anti-corrosion paints for the protection of steel constructions such as electricity pylons or bridges. Until recently, little has been known about the behavior of these Pb compounds in soils. Therefore, three pylon soils and six red lead anti-corrosion paints were characterized in terms of solubility, Pb mineral composition, extractability, sorption and desorption, and the chemical speciation of Pb in soil extracts. The pylon soils were characterized by moderate total Pb concentrations (≈700 mg kg^?1), while NH₄NO₃ extractable Pb was exceptionally high (up to 15% of total Pb). In soil extracts, the free Pb²⁺ fraction ranged from 33 to 81% of total soluble Pb. The equilibrium concentration of Pb derived from Pb₃O₄ in ultra-pure water reached 68.5 mg L^?1. This high solubility explains the observed high extractability in soils and contradicts earlier reports of much lower water solubilities of the compound.