Gas exchange and resource-use patterns along a Mediterranean successional gradient

Abstract. Gas exchange, leaf-nitrogen concentration and water potential were measured in early and late spring in early successional herbaceous plants occurring after cutting and after fire, and in mature woody species from the Mediterranean climax community Quercetum ilicis in central Italy. Net photosynthesis peaked in early spring in all species studied when values for temperature and light were lower but leaf-nitrogen content was higher as compared to late spring, suggesting that nitrogen more than energy input controlled photosynt-hetic rates. Herbaceous pioneer species occurring after cutting showed higher field photo synthetic capacity than evergreen climax trees and shrubs. By contrast, net photosynthesis of herbaceous species occurring in a persistent stage after fire, was in the same range as that of climax trees. This evidence suggests that carbon-gaining appears to be partly related to the dynamic stage of succession and not solely to the growth form.     

Beneficial effects of n-hexane bark extract of Onosma echioides L. on diabetic peripheral neuropathy

Onosma echioides Linn (Boraginaceae) is the most frequently used curative herb widely used for kidney obstruction, sciatic pain, and gout. The present study was designed to investigate the therapeutic effects of n-hexane bark extract of O. echioides (OE) L. root in vivo against Streptozotocin-induced diabetic neuropathy in SD rats. For in vivo activity, the experiment was categorized into five different groups (n = 5). Group-I was considered as nondiabetic/normal control (NC) treated with 0.5% carboxymethyl cellulose (CMC), Group II as diabetic control, Group-III, IV, and V served as diabetic treated with OE 50, OE 100, and pregabalin at a dose of 50, 100, and 10 mg/kg body weight, orally, respectively. Body weight, blood glucose, oral glucose tolerance test, behavioral studies (motor coordination test, thermal hyperalgesia, cold allodynia, locomotor activity, oxidative biomarkers (thio barbituric acid reactive substances [TBARS], superoxide dismutase [SOD], glutathione [GSH], and catalase), and histopathology of the sciatic nerve were performed. Treatment with OE showed a dose-dependent increase in neuroprotective activity by improving the myelination and decreasing the axonal swelling of nerve fibers. The verdicts of behavioral activities showed a remarkable effect on animals after the treatment of extract and standard drug pregabalin. In conclusion, our findings supported the traditional application of OE and explored its importance in the management of diabetic neuropathy. Additional clinical experiments may provide novel therapeutic drugs for diabetes and its complications.     

Reduced sexual dimorphism in upper arm muscle circumference associated with protein-deficient diet in a South American population

Animal experiments have demonstrated that individuals exhibit differing tendencies to arrest growth and resorb muscle tissue under nutritional stress. Since placental and adrenocortical hormones are active in promoting muscle tissue resorption, sex differences may exist. In order to identify such sex differences, the upper arm circumferences of 362 individuals, aged one to 60 years, living in an area of chronic protein-calorie malnutrition were compared by age and sex with published data collected from U.S. and highland Peruvian populations. Sexual dimorphism for arm muscle circumference in the malnourished population is less than in U.S. samples of comparable age-categories. The highland population is closer to U.S. samples in the degree of dimorphism. The reduction in muscle circumference of males in the malnourished population appears to be the cause of the comparatively greater similarity of the sexes where protein-calorie malnutrition is experienced from infancy through adolescence. High muscle relief and excellent tonus in these same males indicate that reduced muscle circumference is not the result of flaccidity or higher ratios of compressible fat to muscle tissue. Reduction of muscle tissue in undernourished males is a reduction in total metabolic demand. Such reductions are adaptive in areas of chronic nutritional stress.     

Synthesis of 5‐tert‐butyl‐1‐(3‐tert‐butyldimethylsiloxy)phenyl‐4,4‐dimethyl‐2,6,7‐trioxabicyclo[3.2.0]heptanes and their fluoride‐induced chemiluminescent decomposition: effect of a phenolic electron donor on the CIEEL decay rate in aprotic polar solvent

Four bicyclic dioxetanes bearing a phenolic substituent, 3‐tert‐butyldimethylsiloxy‐4‐chlorophenyl ( 3a ), 5‐tert‐butyldimethylsiloxy‐4‐chloro‐2‐ethylphenyl ( 3b ), 5‐tert‐butyldimethylsiloxy‐2‐ethylphenyl ( 3c ), and 3‐tert‐butyldimethylsiloxy‐4‐ethylphenyl ( 3d ), were synthesized. All dioxetanes 3a – 3d gave intense blue light on treatment with tetrabutylammonium fluoride (TBAF) in DMSO or acetonitrile. Kinetic study on the fluoride‐induced CIEEL decay of these dioxetanes 3a – 3d and the parent dioxetane 2b revealed that the para‐substitution with chlorine on the phenolic moiety of dioxetane increases free energy of activation (ΔG?), while the para‐substitution with ethyl on the aryl decreases ΔG?. On the other hand, substitution with an ethyl at the ortho‐position instead of the para‐position was found to increase ΔG? and to suppress the CIEEL decay. This fact is attributed to the steric factor of the ortho‐ethyl group which would prevent the aromatic ring from rotating freely around the axis joined to the peroxide ring, and supports the suggestion for a CIEEL‐active dioxetane bearing a phenolic moiety that an intramolecular electron transfer occurs preferentially from the phenolic donor to O–O of the dioxetane ring, when the aromatic ring lies in a certain conformation(s). Copyright © 2002 John Wiley & Sons, Ltd.     

Scale-dependent interactions between intrinsic and extrinsic processes reduce variability in protist populations

Interactions between intrinsic processes and extrinsic fluctuations can positively impact population persistence in ways often not predicted by classic ecological models. These interactions only arise when the intrinsic and extrinsic processes operate on the proper relative scales in time or space. Both metapopulation theory and resonance/attenuation theory suggest that interactions which lower population variability will occur when the intrinsic and extrinsic process occur on similar time scales. I performed an aquatic protist microcosm experiment to investigate how the relative frequencies of extrinsic density perturbations and intrinsic resource pulses impacted population variability. Population variability was lowest in the treatments of intermediate frequency, in which the extrinsic fluctuations and intrinsic processes were on the same time scale. This result is consistent with general theoretical predictions, and empirically documents the importance of considering scale in interactions between intrinsic and extrinsic processes that positively impact population persistence.     

Abalone I: Analyzing Mark-Recapture-Recovery Data Incorporating Growth and Delayed Recovery

Abalone are semimobile marine gastropods that form the basis of Australia's second most valuable fishery. A site off the coast of Port Arthur, Tasmania, was visited on six occasions. On each occasion, any unmarked live abalone found were marked with a unique identification number and were recorded. Any previously marked abalone found had its identification number and whether or not it was still alive recorded. This results in integrated mark-recapture-recovery data, as in Catchpole et al. (1998, Biometrics 54, 33-46). During the study period, abalone grew in size, and we model the survival of individuals as a function of their size, estimated from a fitted growth curve. The shells of dead animals are long lasting, and we extend existing methodology to allow for the possibility that an animal found dead may have been dead but overlooked for several visits.     

Effects of an inhomogeneous magnetic field on flowing erythrocytes

Effects of an inhomogeneous magnetic field on narrow erythrocyte streams in a wide and transparent laminar buffer flow were studied. The stream line of erythrocytes containing paramagnetic hemoglobin showed distinct displacement toward the stronger magnetic field. The displacement increased in the order, oxygenated erythrocytes (no displacement), erythrocytes containing cyanomethemoglobin, deoxygenated erythrocytes, erythrocytes containing methemoglobin in the high spin state; more precisely the displacement was proportional to the square of the paramagnetic moment of hemoglobin contained in the erythrocytes. In addition, the displacement was proportional to the product of the magnetic flux density and its gradient, and approximately proportional to the hematocrit of the flowing-erythrocyte suspension, and was much larger than that calculated for a single erythrocyte. These phenomena could be successfully interpreted by the interaction of paramagnetic erythrocytes with the inhomogeneous magnetic field, the resistance force (Stokes Law) from the bulk water, and the hydrodynamic interaction between erythrocytes.     

Effects of clipping and soil compaction on growth,morphology and mycorrhizal colonization of Schizachyrium scoparium,a C4 bunchgrass

Summary A factorial design of clipping and compaction was used to study the responses of Schizachyrium scoparium and its mycorrhizal symbionts to these stresses. All treatment combinations significantly reduced the growth and biomass of plants relative to controls. Compaction significantly reduced tillering and crown expansion while clipping increased tillering early in the growing season and reduced it later. Mycorrhizal colonization of roots was highest in the clipped plots and lowest in compacted plots. Spore number was highest in compacted plots and lowest in clipped plots. It appears that spore number may be negatively correlated with root growth since any treatment that reduced plant growth yielded higher spore numbers. The combination of clipping and compaction reduced plant growth the most, but had intermediate effects on mycorrhizal colonization and spore number.     

Cooperation of epidermis and inner tissues in auxin-mediated growth of maize coleoptiles

The function of the epidermis in auxinmediated elongation growth of maize (Zea mays L.) coleoptile segments was investigated. The following results were obtained: i) In the intact organ, there is a strong tissue tension produced by the expanding force of the inner tissues which is balanced by the contracting force of the outer epidermal wall. The compression imposed by the stretched outer epidermal wall upon the inner tissues gives rise to a wall-pressure difference which can be transformed into a water-potential difference between inner tissues and external medium (water) by removal of the outer epidermal wall. ii) Peeled segments fail to respond to auxin with normal growth. The plastic extensibility of the inner-tissue cell walls (measured with a constant-load extensiometer using living segments) is not influenced by auxin (or abscisic acid) in peeled or nonpeeled segments. It is concluded that auxin induces (and abscisic acid inhibits) elongation of the intact segment by increasing (decreasing) the extensibility specifically in the outer epidermal wall. In addition, tissue tension (and therewith the pressure acting on the outer epidermal wall) is maintained at a constant level over several hours of auxin-mediated growth, indicating that the inner cells also contribute actively to organ elongation. However, this contribution does not involve an increase of cell-wall extensibility, but a continuous shifting of the potential extension threshold (i.e., the length to which the inner tissues would extend by water uptake after peeling) ahead of the actual segment length. Thus, steady growth involves the coordinated action of wall loosening in the epidermis and regeneration of tissue tension by the inner tissues. iii) Electron micrographs show the accumulation of striking osmiophilic material (particles of approx. 0.3 m diameter) specifically at the plasma membrane/cell-wall interface of the outer epidermal wall of auxin-treated segments. iv) Peeled segments fail to respond to auxin with proton excretion. This is in contrast to fusicoccin-induced proton excretion and growth which can also be readily demonstrated in the absence of the epidermis. However, peeled and nonpeeled segments show the same sensitivity to protons with regard to the induction of acid-mediated in-vivo elongation and cell-wall extensibility. The observed threshold at pH 4.5–5.0 is too low to be compatible with a second messenger function of protons also in the growth response of the inner tissues. Organ growth is described in terms of a physical model which takes into account tissue tension and extensibility of the outer epidermal wall as the decisive growth parameters. This model states that the wall pressure increment, produced by tissue tension in the outer epidermal wall, rather than the pressure acting on the inner-tissue walls, is the driving force of growth.Abbreviations and symbols E _el, E _pl elastic and plastic in-vitro cell-wall extensibility, respectively - E _tot E _el+E _pl - FC fusicoccin - IAA indole-3-acetic acid - IT inner tissue - ITW inner-tissue walls - OEW outer epidermal wall - osmotic pressure - P wall pressure - water potential     

Growth responses of tropical forage plant species to vesicular-arbuscular mycorrhizae

Summary Growth and mineral uptake of twenty-four tropical forage legumes and grasses were compared under glasshouse conditions in a sterile low P oxisol, one part inoculated and the other not inoculated with mycorrhizal fungi. Shoot and root dry weights and total uptake of P, N, K, Ca, and Mg of all the test plants were significantly increased by mycorrhizal inoculation. Mycorrhizal inoculation, with few exceptions, decreased the root/shoot ratio. Non-mycorrhizal plants contained always lower quantities of mineral elements than mycorrhizal plants. Plant species showed differences in percentage mycorrhizal root length and there was no correlation between percentage mycorrhizal infection and plant growth parameters. A great variation in dependence on mycorrhiza was observed among forage species. Total uptake of all elements by non-mycorrhizal legumes and uptake of P, N and K by non-mycorrhizal grasses correlated inversely with mycorrhizal dependency. Mycorrhizal plants of all species used significantly greater quantities of soil P than the nonmycorrhizal plants. Utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorrhizal dependency.