Nutrient conservation strategies in native Andean‐Patagonian forests

Abstract. Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life‐span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C‐, N‐, P‐, K‐ and lignin‐concentrations in mature and senescent leaves of ten native woody species within the functional groups: broad‐leaved deciduous species, broad‐leaved evergreens and conifers. We also examined mycorrhizal associations in all species. Nutrient concentration in mature leaves and N‐ resorption were higher in broad‐leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N‐resorption and high lignin/N ratios in senescent leaves. P‐ and K‐resorptions did not differ among functional groups. Broad‐leaved evergreens exhibited a species‐dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N‐fertility. Despite the high P‐retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad‐leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad‐leaved evergreen Lomatia hirsuta, would be possibly explaining why P is less limiting than N in these forests.     

Manganese-54 accumulation by Chlorella spp., Daphnia magna and yellow perch (Perca flavescens)

Concentration factor and biological half-life of ⁵⁴Mn were determined in three species representing an ecologically and economically important food chain. Green algae (Chlorella spp.), Daphnia magna and yellow perch (Perca flavescens) were exposed to ⁵⁴Mn in water and assayed for ⁵⁴Mn uptake. Steady state concentration factors computed from the laboratory data for algae, Daphnia and perch were 4230, 17 000 and 11, respectively. Respective biological half-lives were 1.6, 1.2 and 8.3 days.     

Effects of detergents on catalytic activity of human endometase/matrilysin 2, a putative cancer biomarker

Matrix metalloproteinases (MMPs) are a family of hydrolytic enzymes that play significant roles in development, morphogenesis, inflammation, and cancer invasion. Endometase (matrilysin 2 or MMP-26) is a putative early biomarker for human carcinomas. The effects of the ionic and nonionic detergents on catalytic activity of endometase were investigated. The hydrolytic activity of endometase was detergent concentration dependent, exhibiting a bell-shaped curve with its maximum activity near the critical micelle concentration (CMC) of nonionic detergents tested. The effect of Brij-35 on human gelatinase B (MMP-9), matrilysin (MMP-7), and membrane-type 1 MMP (MT1-MMP) was further explored. Their maximum catalysis was observed near the CMC of Brij-35 (∼ 90 μM). Their IC₅₀ values were above the CMC. The inhibition mechanism of MMP-7, MMP-9, and MT1-MMP by Brij-35 was a mixed type as determined by Dixon’s plot; however, the inhibition mechanism of endometase was noncompetitive with a K_i value of 240 μM. The catalytic activities of MMPs are influenced by detergents. Monomer of detergents may activate and stabilize MMPs to enhance catalysis, but micelle of detergents may sequester enzyme and block the substrate binding site to impede catalysis. Under physiological conditions, a lipid or membrane microenvironment may regulate enzymatic activity.     

Relationship between the concentration of sugars in the roots and VA mycorrhizal infection

Summary The VA-infected wheat varieties showed an increase of total (Lozano var.) and reducing (Lozano and Pane vars.) sugars in their root extracts. However, no clear relationship between sugar concentration in the root and VA mycorrhizal infection level could be established.In addition, the VA mycorrhizal hosts sorghum, alfalfa, sunflower and maize, and non-host radish and cabbage plants were tested for sugar content in their root extracts after fifteen days of growth. Sugars present in the root extracts of these plants did not seem to be a decisive factor in plant susceptibility to VA infection.     

An Aphid-Secreted Salivary Protease Activates Plant Defense in Phloem

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The glands of Tamarix aphylla: a system for salt recretion or for carbon concentration?

During periods of high atmospheric humidity, twigs of Tamarix aphylla (L.) Karst. become covered by an alkaline solution. The pH of that solution fluctuates between 8.0 – 8.5 in the dark and 10.5 during the light hours. Such a solution, produced by the glands, constitutes an efficient trap for atmospheric CO₂. Upon the periodic drop in pH, much of the preabsorbed carbon may gradually be released from the solution. This enriches the immediate surroundings of the twigs with CO₂ for prolonged periods of time. The expected concentrations of CO₂, at the boundary layer between the atmosphere and the surfaces of the twigs, are over 1 000 ppm. As net photosynthesis of T. aphylla reaches maximal rates only at CO₂ concentrations of above 500 ppm, the plants may benefit from this extra source of carbon and may exploit it for maximal assimilation during the early morning hours. Thus, the "salt glands'of Tamarix , which are liable for the production of the alkaline recretum, may serve a triple purpose: (a) removal of excess salts out of the twigs, (b) provision of a cover of hygroscopic solutes that moistens the twigs and shortens the duration of transpiration, and (c) providing the plants with an environment enriched in CO₂.     

Uptake,Transport and Storage of Cardenolides in Foxglove. Cardenolide Sinks and Occurrence of Cardenolides in the Sieve Tubes of Digitalis lanata1

Cardiac glycoside transport was investigated on the organ and whole plant level. Uptake experiments were carried out with shoot and root cultures of Digitalis lanata. In both systems primary cardenolides, i.e., those with a terminal glucose in their oligosaccharide side chain, were taken up against their concentration gradient, whereas the glucose-free secondary cardenolides were not. Active uptake of primary cardenolides was further evidenced by KCN inhibition of uptake. Using plantlets grown in vitro the long-distance transport of primary cardenolides from the leaves to the roots was demonstrated. Cardenolides were also detected in etiolated leaves, induced on plants with green leaves, which are supposed to be unable to synthezise cardenolides de novo, providing further evidence for long-distance transport. Several primary cardenolides were detected in the honeydew excreted by aphids fed on Digitalis lanata leaves, indicating that the phloem is a transporting tissue for cardenolides. On the other hand, the xylem sap obtained by applying the pressure-chamber technique was cardenolide-free. It was concluded that in Digitalis primary cardenolides serve as both the transport and the storage form of cardenolides. After their synthesis they are either stored in the vacuoles of the source tissue or loaded into the sieve tubes, from which they are unloaded at other sites where they are trapped in the vacuoles of the respective sink tissue.     

Translocation - A key factor limiting the efficiency of nitrogen fixation in legume nodules

A hypothesis is presented that the availability of water for export of nitrogenous products from legume nodules is a major factor limiting the efficiency of symbiotic nitrogen fixation. Water for export of solutes in the xylem probably depends largely on the import of water and reduced carbon in the phloeum, and one function of respiration may be to dispose of reduced carbon in order to increase the supply of water. A second hypothesis presented is that control of gas diffusion in soybean nodules is largely restricted to the cortex nearby the vascular bundles, thus making possible the linkage of solute balances in xylem and phloem with resistance to diffusion. These concepts are used in a re-examination of literature on manipulations of nodules and nodulated plants such as lowering of light levels, water stress, defoliation, stem girdling, and alteration of oxygen supply. The concept of translocation as a major factor limiting efficiency of symbiotic fixation is consistent with the failure of superior rhizobial isolates to improve N input significantly, and this limitation could also prevent exploitation of superior bacterial symbionts in the future     

Honeydew amino acids in relation to sugars and their role in the establishment of ant-attendance hierarchy in eight species of aphids feeding on tansy (Tanacetum vulgare)

Abstract. The ratio of the concentration of honeydew total amino acids to total sugars in the honeydew of eight species of aphids, all feeding on tansy, Tanacetum vulgare (L.), was determined and correlated with honeydew production and ant‐attendance. The honeydew of the five ant‐attended aphid species [Metopeurum fuscoviride (Stroyan), Trama troglodytes (v. Hayd), Aphis vandergooti (Börner), Brachycardus cardui (L.), Aphis fabae (Scopoli)] was rich in total amino acids, ranging from 12.9 to 20.8 nmol µL^?1 compared with the unattended aphid Macrosiphoniella tanacetaria (Kalt.) with only 3 nmol µL^?1. Asparagine, glutamine, glutamic acid and serine (all nonessential amino acids) were the predominant amino acids in the honeydew of all species. The total concentration of amino acids in the phloem sap of tansy was much higher (78.7 nmol µL^?1) then in the honeydew samples, and the predominant amino acids were glutamate (34.3%) and threonine (17.7%). A somewhat unexpected result was the finding that those aphid species with the highest total amino acid concentration in the honeydew always had the highest concentration of sugars. The lowest amino acid–sugar combined value was 104–28.8 nmol µL^?1 in the non ant‐attended species M. tanacetaria, and the highest value was an average of 270–89.9 nmol µL^?1 for the three most intensely attended aphid species M. fuscoviride, A. vandergooti and T. troglodytes. There is no evidence that any single amino acid or group of amino acids in the honeydew acted as an attractant for ant‐attendance in these eight aphid species. The richness of the honeydew (rate of secretion × total concentration of sugars), along with the presence of the attractant sugar melezitose, comprised the critical factors determining the extent of ant‐attendance of the aphids feeding on T. vulgare. The high total amino acid concentration in sugar‐rich honeydews can be explained by the high flow‐through of nutrients in aphids that are particularly well attended by ants.