Responses of ectomycorrhizal Populus tremuloides and Betula papyrifera seedlings to salinity

Roots of trembling aspen (Populus tremuloides Michx.) and paper birch (Betula papyrifera Marsh.) seedlings were inoculated with Hebeloma crustuliniforme or Laccaria bicolor and treated with 25 mM NaCl for 6 weeks. Both tree species appeared to be relatively tolerant of the applied NaCl treatment and did not develop visible leaf symptoms that are characteristic of salt injury. Salt treatment reduced total dry weights in aspen and birch, but did not significantly affect transpiration rates and root hydraulic conductance. Salt-treated ectomycorrhizal aspen maintained higher root hydraulic conductance compared with non-mycorrhizal plants. Na and Cl concentrations increased in shoots and roots of mycorrhizal and non-mycorrhizal aspen and birch in response to NaCl treatment. Roots of NaCl-treated aspen inoculated with H. crustuliniforme had over twofold higher concentrations of Na compared with non-mycorrhizal NaCl-treated plants. Similarly to aspen, Na and Cl concentrations increased in roots and shoots of NaCl-treated birch seedlings. However, in birch, there were no significant differences in Na and Cl concentrations between mycorrhizal and non-mycorrhizal plants. The results suggest that salt exclusion by the ectomycorrhizal associations is host-specific or/and that the processes leading to salt exclusion are activated in ectomycorrhizal plants by a threshold salt level which may vary between plant species.     

Light-induced transpiration alters cell water relations in figleaf gourd (Cucurbita ficifolia) seedlings exposed to low root temperatures

Water relation parameters including elastic modulus (epsilon), half-times of water exchange (T(w)(1/2)), hydraulic conductivity and turgor pressure (P) were measured in individual root cortical and cotyledon midrib cells in intact figleaf gourd (Cucurbita ficifolia) seedlings, using a cell pressure probe. Transpiration rates (E) of cotyledons were also measured using a steady-state porometer. The seedlings were exposed to low ambient (approximately 10 micromol m(-2) s(-1)) or high supplemental irradiance (approximately 300 micromol m(-2) s(-1) PPF density) at low (8 degrees C) or warm (22 degrees C) root temperatures. When exposed to low irradiance, all the water relation parameters of cortical cells remained similar at both root temperatures. The exposure of cotyledons to supplemental light at warm root temperatures, however, resulted in a two- to three-fold increase in T(w)(1/2) values accompanied with the reduced hydraulic conductivity in both root cortical (Lp) and cotyledon midrib cells (Lp(c)). Low root temperature (LRT) further reduced Lp(c) and E, whether it was measured under low or high irradiance levels. The reductions of Lp as the result of respective light and LRT treatments were prevented by the application of 1 microM ABA. Midrib cells required higher concentrations of ABA (2 microM) in order to prevent the reduction in Lp(c). When the exposure of cotyledons to light was accompanied by LRT, however, ABA proved ineffective in reversing the inhibition of Lp. LRT combined with high irradiance triggered a drastic 10-fold reduction in water permeability of cortical and midrib cells and increased epsilon and T(w)(1/2) values. Measurement of E indicated that the increased water demand by the transpiring plants was fulfilled by an increase in the apoplastic pathway as principal water flow route. The importance of water transport regulation by transpiration affecting the hydraulic conductivity of the roots is discussed.     

Responses of ectomycorrhizal American elm (Ulmus americana) seedlings to salinity and soil compaction

American elm (Ulmus americana) seedlings were either non-inoculated or inoculated with Hebeloma crustuliniforme, Laccaria bicolor and a mixture of the two fungi to study the effects of ectomycorrhizal associations on seedling responses to soil compaction and salinity. The seedlings were grown in the greenhouse in pots containing non-compacted (0.4 g cm^?3 bulk density) and compacted (0.6 g cm^?3 bulk density) soil and subjected to 60 mM NaCl or 0 mM NaCl (control) treatments for 3 weeks. All three fungal inocula had similar effects on the responses of elm seedlings to soil compaction and salt treatment. In non-compacted soil, ectomycorrhizal fungi reduced plant dry weights, root hydraulic conductance, but did not affect leaf hydraulic conductance and net photosynthesis. When treated with 60 mM NaCl, ectomycorrhizal seedlings had several-fold lower leaf concentrations of Na⁺ compared with the non-inoculated plants. Soil compaction reduced Na⁺ leaf concentrations in non-ectomycorrhizal plants and decreased dry weights, gas exchange and root hydraulic conductance. However, in ectomycorrhizal plants, soil compaction had little effect on the leaf Na⁺ concentrations and on other measured growth and physiological parameters. Our results demonstrated that ECM associations could be highly beneficial to plants growing in sites with compacted soil such as urban areas.     

Boreal forest plant species responses to pH: ecological interpretation and application to reclamation

Aims

Reclamation following oil sands mining in northeastern Alberta (Canada) creates adverse reforestation soil conditions, including extreme pH values. We elucidated pH tolerance limits of boreal plant species and how pH affects nutrient uptake in these plants.

Methods

We measured growth, gas exchange, and foliar nutrient concentration of 15 common northern boreal forest plants after eight weeks exposure to root zone pH ranging from 5.0 to 9.0. Cluster analyses were used to group these species based on their pH responses.

Results

Based on their growth and gas exchange responses to pH, the 15 plant species could be divided into five groups, each of which contained species that commonly co-occur in particular boreal forest site types. For the foliar nutrient responses to pH, the 15 species could be grouped into only two categories; both showed decreases in foliar N, P, Fe and Zn concentration with increasing pH, with a more pronounced effect on the group that included trembling aspen, paper birch and chokecherry.

Conclusions

The evidence of differential adaptation to pH by habitat type suggests the importance of soil pH as a factor affecting boreal plant species distribution and could be helpful for selection of species suitable for reclamation of sites with altered soil pH.

     

NaCl and Na2SO4 alter responses of jack pine (Pinus banksiana) seedlings to boron

Using sand culture, we examined the responses of 6-month-old jack pine (Pinus banksiana Lamb.) seedlings to boron and salinity (sodium chloride and sodium sulfate) treatments. During 4 weeks of treatments, 60 mM NaCl and 60 mM Na₂SO₄ significantly decreased survival, new shoot length, number of new roots, shoot to root dry weight ratio and transpiration rates. When applied in absence of the salts, B had little effect on the measured variables. However, when applied together with salts, B decreased seedling survival, increased needle injury and altered tissue elemental concentrations in jack pine seedlings. In 2 mM B treatment, B concentration was higher in the shoots than in the roots. However, when 2 mM B was present in NaCl and Na₂SO₄ treatments, shoot boron concentration declined and greater proportion of B accumulated in the roots. This shift corresponded to a decline in transpiration rates. In plants treated with NaCl, Na accumulated primarily in the shoots, while in Na₂SO₄-treated plants Na accumulated mostly in the roots. Based on the electrolyte leakage and needle necrosis data, Cl^– appears to be the major factor contributing to seedling injury and B aggravates the injurious effects of NaCl. We suggest that Cl^– may contribute to Na and B toxicity in jack pine by altering cell membrane permeability leading to increased Na concentration in the shoots.     

Splinting or surgery for carpal tunnel syndrome? Design of a randomized controlled trial [ISRCTN18853827]

Background  

Carpal tunnel syndrome is a common disorder, which can be treated with surgery or conservative options. However, there is insufficient evidence and no consensus among physicians with regard to the preferred treatment for carpal tunnel syndrome. Therefore, a randomized controlled trial is conducted to compare the short- and long-term efficacy of surgery and splinting in patients with carpal tunnel syndrome. An attempt is also made to avoid the (methodological) limitations encountered in earlier trials on the efficacy of various treatment options for carpal tunnel syndrome.     

The genus Pyrus L. (Rosaceae) in south-west Europe and North Afkica

A multivariate morphometric study of the genus Pyrus in south-west Europe and North Africa shows that five species may be recognized in the area: P. bourgaeana Decne., P. communis L., P. cordata Dew., P. spinosa Forssk, and P. nivalis Jacq. Some valuable characters for identification of these species are proposed. In particular the width of fruit peduncle, petal size, leaf width and petiole length served to discriminate the taxa. Several names such as P. gharbiona Trab., P. cossonii Rehder (|M= P. longipes Balansa ex Coss. & Durieu) and P. boisseriana Buhse, are regarded as synonyms of P. cordata , while P. marnormis Trab. of P. bourgaeana. Consequently a check-list and a key to these species are provided.     

Cultured endothelial cells produce heparinlike inhibitor of smooth muscle cell growth

Using cultured cells from bovine and rat aortas, we have examined the possibility that endothelial cells might regulate the growth of vascular smooth muscle cells. Conditioned medium from confluent bovine aortic endothelial cells inhibited the proliferation of growth-arrested smooth muscle cells. Conditioned medium from exponential endothelial cells, and from exponential or confluent smooth muscle cells and fibroblasts, did not inhibit smooth muscle cell growth. Conditioned medium from confluent endothelial cells did not inhibit the growth of endothelial cells or fibroblasts. In addition to the apparent specificity of both the producer and target cell, the inhibitory activity was heat stable and not affected by proteases. It was sensitive flavobacterium heparinase but not to hyaluronidase or chondroitin sulfate ABC lyase. It thus appears to be a heparinlike substance. Two other lines of evidence support this conclusion. First, a crude isolate of glycosaminoglycans (TCA-soluble, ethanol-precipitable material) from endothelial cell-conditioned medium reconstituted in 20 percent serum inhibited smooth muscle cell growth; glycosaminoglycans isolated from unconditioned medium (i.e., 0.4 percent serum) had no effect on smooth muscle cell growth. No inhibition was seen if the glycosaminoglycan preparation was treated with heparinase. Second, exogenous heparin, heparin sulfate, chondroitin sulfate B (dermatan sulfate), chondroitin sulfate ABC, and hyaluronic acid were added to 20 percent serum and tested for their ability to inhibit smooth muscle cell growth. Heparin inhibited growth at concentrations as low as 10 ng/ml. Other glycosaminoglycans had no effect at doses up to 10 μg/ml. Anticoagulant and non- anticoagulant heparin were equally effective at inhibiting smooth muscle cell growth, as they were in vivo following endothelial injury (Clowes and Karnovsk. Nature (Lond.). 265:625-626, 1977; Guyton et al. Circ. Res. 46:625-634, 1980), and in vitro following exposure of smooth muscle cells to platelet extract (Hoover et al. Circ. Res. 47:578-583, 1980). We suggest that vascular endothelial cells may secrete a heparinlike substance in vivo which may regulate the growth of underlying smooth muscle cells.