Evaluation of soil saturation, soil chemistry, and early spring soil and air temperatures as risk factors in yellow-cedar decline

Yellow‐cedar (Callitropsis nootkatensis (D. Don) Oerst.) is a valuable tree species that is experiencing a widespread decline and mortality in southeast Alaska. This study evaluated the relative importance of several potential risk factors associated with yellow‐cedar decline: soil saturation, soil aluminum (Al) toxicity or calcium (Ca) deficiency, and air and soil temperature. Data were collected from permanent vegetation plots established in two low‐elevation coastal forests exhibiting broad ranges of cedar mortality. Measurements of each risk factor were contrasted among classified forest zones to indicate if there were strong links with decline. Hydrology alone is weakly associated with yellow‐cedar decline, but could have a predisposing role in the decline by creating exposed conditions because of reduced forest productivity. Yellow‐cedar decline is not strongly associated with soil pH and extractable Al and Ca, but there appears to be Ca enrichment of surface soils by feedback from dead yellow‐cedar foliage. Air and soil temperature factors are strongly associated with decline. Based on these results, an hypothesis is presented to explain the mechanism of tree injury where exposure‐driven tree mortality is initiated in gaps created by soil saturation and then expands in gaps created by the tree‐mortality itself. The exposure allows soils to warm in early spring causing premature dehardening in yellow‐cedar trees and subsequent freezing injury during cold events. Yellow‐cedars growing in the protection of shade or snow are not preconditioned by this warming, and thus not as susceptible to cold injury. Yellow‐cedar decline appears to be associated with regional climate changes, but whether the cause of these changes is related to natural or human‐induced climate shifts remains uncertain. Management implications, the possible role of climate, and recommended research are discussed.     

ATP in cellular calcium-overload by trivalent metal ions

Extracellular Ca²⁺-influx induced by trivalent metal ions (Fe³⁺, Al³⁺, Cr³⁺, In³⁺, Ga³⁺, and La³⁺) in Ehrlich carcinoma cells is enhanced by ATP. This action seems to be related to the high coordination capacity of the ATP ligand that inhibits the polymerization of the solvated cations taking place at physiological pH, and consequently permits their biological activity. A general relationship between induced lipid peroxidation and increased calcium uptake was not found. These results emphasize the ATP role in the toxicity of trivalent metals, and its possible involvement, via cellular calcium overload, in a neurodegenerative process, such as Alzheimer's and Parkinson's diseases, in whose etiology the implication of aluminum and iron has been suggested.     

Effect of pH and aluminum on surface properties of barley roots as determined from water vapor adsorption

Water vapor adsorption isotherms were used for the estimation of surface areas and adsorption energy distribution functions of roots of barley grown at different pH levels and at a toxic Al level (10 mg·dm⁻³), induced at tillering and shooting stages of plants growth. Values of surface area as well as energy distributions were the same for the roots grown at all pH values studied: 2, 4 and 7 and not dependent on the age of the plants indicating that the protons do not alter the physicochemical build-up of the surface of roots. However, significant changes of the root surface properties under the influence of aluminum: increase of surface area, average adsorption energy and amount of highly energetic adsorption sites together with a decrease of low energetic sites were observed.     

Reconstitution of the native mitochondrial outer membrane in planar bilayers. Comparison with the outer membrane in a patch pipette and effect of aluminum compounds

Summary Detergent-free rat brain outer mitochondrial membranes were incorporated in planar lipid bilayers in the presence of an osmotic gradient, and studied at high (1 m KCl) and low (150 mm KCl) ionic strength solutions. By comparison, the main outer mitochondrial membrane protein, VDAC, extracted from rat liver with Triton X-100, was also studied in 150 mm KCl. In 1 m KCl, brain outer membranes gave rise to electrical patterns which resembled very closely those widely described for detergent-extracted VDAC, with transitions to several subconducting states upon increase of the potential difference, and sensitivity to polyanion. The potential dependence of the conductance of the outer membrane, however, was steeper and the extent of closure higher than that observed previously for rat brain VDAC. In 150 mm KCl, bilayers containing only one channel had a conductance of 700 ± 23 pS for rat brain outer membranes, and 890 ± 29 pS for rat liver VDAC. Use of a fast time resolution setup allowed demonstration of open-close transitions in the millisecond range, which were independent of the salt concentration and of the protein origin. We also found that a potential difference higher than approx. ± 60 mV induced an almost irreversible decrease of the single channel conductance to few percentages of the full open state and a change in the ionic selectivity. These results show that the behavior of the outer mitochondrial membrane in planar bilayers is close to that detected with the patch clamp (Moran et al., 1992, Eur. Biophys. J. 20:311–319).The neurotoxicological action of aluminum was studied in single outer membrane channels from rat brain mitochondria. We found that m concentrations of Al Cl₃ and aluminum lactate decreased the conductance by about 50%, when the applied potential difference was positive relative to the side of the metal addition.The authors thank Dr. O. Moran for helpful discussions, Dr. M. Colombini for a sample of polyanion, and the Sharing Company for financial support to Dr. T. M. This work was partly supported by funds from the Ministero dell' Universitá e della Ricerca Scientifica e Tecnologica of Italy.     

Phosphorus availability to maize from partially acidulated phosphate rocks and phosphate rocks compacted with triple superphosphate

Two phosphate rocks (PR), moderately reactive Hila PR from Colombia and slightly reactive Capinota PR from Bolivia, were compacted with triple superphosphate (TSP) such that 50% of total P in the mixture was in water-soluble form. The effectiveness of these materials as phosphorus sources was compared with that of partially acidulated phosphate rocks (PAPR) at 50% acidulation with sulfuric acid and TSP in Hartsells silt loam (pH 4.5) with maize as the test crop. Huila PAPR and Huila PR compacted with TSP were as effective as TSP as phosphorus sources. Huila PR was only half as effective. The slightly reactive Capinota PR with 8.8% Al₂O₃ + Fe₂O₃ content was not suited for direct application, and Capinota PAPR was only half as effective as TSP. Capinota PR compacted with TSP, however, was as effective as TSP. PR compacted with TSP, urea, and KCl was no more effective as phosphorus source than PR compacted with TSP alone.     

Effect of high nonexchangeable aluminium on nitrogen and phosphorus availability in a humus-rich acid forest soil

The effect of high nonexchangeable aluminum on availability of nitrogen (N) and phosphorus (P) was studied in a Cryptopodzolic soil (Cademario) derived from mica schist in southern Switzerland. The research involved a greenhouse pot experiment comparing growth of barley on soil samples of three soil layers (10- to 25-, 40- to 60- and 70- to 90 cm) of the Cademario profile, representing a range of Al and organic matter properties, with the 10- to 40 cm layer of a profile of an acidic brown earth (Haplumbrept), derived from cherty limestone. The experiment, which included four nutrient treatments [check, N₀ (PKS), P₀ (NKS) and full (NPKS)], lime and no lime treatments and four replicates, was supplemented by soil chemical analysis. Results showed that liming alone produced greater yield responses in the Cademario soil than N or P added singly or together. On unlimed soils, barley yield for check, N₀, and P₀ treatments showed a positive linear relation with exchangeable Ca of soils and a negative linear relation with organically-complexed Al. Failure of liming to influence P_av, especially when combined with P fertilization, suggests that P was quickly absorbed on highly active surfaces formed from initially exchangeable Al.This research is a cooperative effort of the Arizona Agricultural Experiment Stations, Journal Article No. 7100 and the Swiss Federal Institute for Forest, Snow and Landscape; it was supported by the National Science Foundation, USA, Grant No. INT-8304490, and the Swiss National Science Foundation, Grant No. 2.919-803.This research is a cooperative effort of the Arizona Agricultural Experiment Stations, Journal Article No. 7100 and the Swiss Federal Institute for Forest, Snow and Landscape; it was supported by the National Science Foundation, USA, Grant No. INT-8304490, and the Swiss National Science Foundation, Grant No. 2.919-803.     

生长素及其运输蛋白对植物铝胁迫的响应

铝对植物的毒害作用主要表现为抑制根尖生长,而根尖生长与生长素及其运输密切相关,铝可能影响了生长素及其代谢过程,但目前尚不清楚生长素及其运输蛋白如何参与植物应对铝胁迫响应。本文通过分析、总结前人研究,并结合自己的前期研究结果,初步阐述生长素或其运输蛋白对植物铝胁迫的响应,即铝影响生长素代谢的相关基因,干扰根尖生长素运输蛋白在细胞内分布及其囊泡运输,调控生长素的极性运榆,进而抑制根尖生长。另一方面,生长素或其运输蛋白又参与了植物应对铝胁迫过程,这主要体现在参与了植物铝毒信号传递、根系铝内置化过程和减缓铝诱导的氧化胁迫。最后,本文提出了生长素及其运输蛋白对植物铝胁迫响应的可能模型。     

外源NO对铝毒下水稻根系生长和抗氧化系统的影响

以水稻品种‘浙辐802’为材料,采用水培法研究铝毒下外源NO对幼苗根系生长、活性氧产生和抗氧化酶活性的影响,探讨外源NO提高水稻耐铝性的生理生化机制。结果显示:(1)0.05mmol/L Al显著抑制水稻根系生长,促使根尖Al、胼胝质、过氧化氢(H2O2)和超氧阴离子自由基(O-·2)含量显著增加;而外源0.1mmol/L的NO供体亚硝基铁氰化钠(sodium nitroprusside,SNP)预处理能使铝毒下水稻幼苗根相对伸长率及根尖NO含量分别增加34.96%和12.86%,根尖Al和相对胼胝质含量分别下降83.04%和31.93%,表明NO可部分缓解铝毒害,且这种作用与内源NO含量变化有关。(2)外源NO同时使铝毒下水稻幼苗根尖H2O2和O-·2含量分别下降15.43%和12.93%,使超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性显著上升,且外源NO的该种作用可以被0.075mmol/L NO清除剂(carboxy-PTIO,cPTIO)所逆转。研究表明,外源NO在调节活性氧代谢以维持细胞膜结构稳定,进而有效减轻Al对水稻根系的损伤上起着重要作用。     

外源IAA增强丹波黑大豆抗铝性的生理机制

以铝耐受型丹波黑大豆(RB)幼苗为供试材料,考察了不同浓度铝胁迫下添加外源IAA对RB根尖内源IAA、H2O2、MDA、铝含量、柠檬酸分泌量以及质膜H+-ATPase活性的影响,探讨外源IAA增强RB抗铝能力的生理机制。结果显示:(1)经25、50和200μmol·L-1 AlCl3胁迫处理24h后,RB根尖IAA含量、柠檬酸分泌量和质膜H+-ATPase活性均表现为先上升后下降的趋势,而H2O2、MDA和根尖铝含量却随着铝处理浓度的增加呈显著上升趋势。(2)与单独25、50和200μmol·L-1 AlCl3胁迫处理相比,添加50μmol·L-1外源IAA后使得RB根尖铝、MDA和H2O2含量均显著降低,同时使RB根尖柠檬酸分泌量分别相应增加到单独处理的2.39、1.73和6.85倍,且其相应的质膜H+-ATPase活性也增加了1.09、1.74和1.45倍。研究表明,外源IAA能通过增强丹波黑大豆根尖柠檬酸的分泌量和质膜H+-ATPase活性来提高其对铝胁迫的抗性,明显缓解铝毒害作用。     

Aggregation effects due to aluminum adsorption to cell walls of the unicellular green alga Scenedesmus obtusiusculus

Cells of the unicellular green alga Scenedesmus obtusiusculus Chod. were cultivated for 2–24 h in nutrient media with low (60 ?mol/L) or high (1000 ?mol/L) phosphorus (P) concentration, and in the presence or absence of 222 ?mol/L aluminum chloride (Al). Cell aggregation was studied by using light microscope, sedimentation and centrifugation. After 2 h, Al was adsorbed to the cell surface and cell aggregates were formed by the attraction of the cells to each other. Aluminum is bound by the negative charges of the cell walls, and studies at different pH showed that a high proportion of positively charged Al forms promote cell aggregation. This effect was most pronounced in low phosphorus cultures as phosphate reduces the effect of Al on cell aggregation by forming aluminum‐phosphate. Algae cultivated in the absence of Al did not show any cell aggregation tendencies.