Rice ACID PHOSPHATASE 1 regulates Pi stress adaptation by maintaining intracellular Pi homeostasis

The concentration and homeostasis of intracellular phosphate (Pi) are crucial for sustaining cell metabolism and growth. During short-term Pi starvation, intracellular Pi is maintained relatively constant at the expense of vacuolar Pi. After the vacuolar stored Pi is exhausted, the plant cells induce the synthesis of intracellular acid phosphatase (APase) to recycle Pi from expendable organic phosphate (Po). In this study, the expression, enzymatic activity and subcellular localization of ACID PHOSPHATASE 1 (OsACP1) were determined. OsACP1 expression is specifically induced in almost all cell types of leaves and roots under Pi stress conditions. OsACP1 encodes an acid phosphatase with broad Po substrates and localizes in the endoplasmic reticulum (ER) and Golgi apparatus (GA). The phylogenic analysis demonstrates that OsACP1 has a similar structure with human acid phosphatase PHOSPHO1. Overexpression or mutation of OsACP1 affected Po degradation and utilization, which further influenced plant growth and productivity under both Pi-sufficient and Pi-deficient conditions. Moreover, overexpression of OsACP1 significantly affected intracellular Pi homeostasis and Pi starvation signalling. We concluded that OsACP1 is an active acid phosphatase that regulates rice growth under Pi stress conditions by recycling Pi from Po in the ER and GA.     

Regulation of gene expression by pH of the growth medium in Aspergillus nidulans

Summary In the fungus Aspergillus nidulans the levels of a number of enzymes whose location is at least in part extracellular (e.g. acid phosphatase, alkaline phosphatase, phosphodiesterase) and of certain permeases (e.g. that for -amino-n-butyrate) are controlled by the pH of the growth medium. For example, at acidic pH, levels of acid phosphatase are high and those of alkaline phosphatase are low whereas at alkaline pH the reverse is true. Mutations in five genes, palA, B, C, E and F, mimic the effects of growth at acid pH whereas mutations in pacC mimic the effects of growth at alkaline pH. palA, B, C, E and F mutations result in an intracellular pH (pH_in) which is more alkaline than that of the wild type whereas pacC mutations result in a pH_in more acidic than that of the wild type. This indicates that these mutations exert their primary effects on the regulation of gene expression by pH rather than on the pH homeostatic mechanism but that the expression of at least some component(s) of the pH homeostatic mechanism is subject to the pH regulatory system. It is suggested that pacC might be a wide domain regulatory gene whose product acts positively in some cases (e.g. acid phosphatase) and negatively in others (e.g. alkaline phosphatase). The products of palA, B, C, E and F are proposed to be involved in a metabolic pathway leading to synthesis of an effector molecule able to prevent the (positive and negative) action of the pacC product.These genes are, to our knowledge, the first examples of genes involved in the regulation of extracellular enzyme and permease synthesis by the pH of the growth medium to be described in any organism.     

UPTAKE OF CADMIUM BY FRESHWATER GREEN ALGAE: EFFECTS OF PH AND AQUATIC HUMIC SUBSTANCES1

The effects of humic substances and low pH on short‐term Cd uptake by Pseudokirchneriella subcapitata (Korshikov) Hindak and Chlamydomonas reinhardtii Dang were investigated under defined exposure conditions. The uptake experiments were run in the presence of either a synthetic organic ligand (nitrilotriacetate) or natural organic ligands (Suwannee River fulvic or humic acid). An ion‐exchange method was used to measure the free Cd²⁺ concentrations in the exposure solutions. At pH 5, measured free Cd²⁺ concentrations agreed with estimations made using the geochemical equilibrium model WHAM, but at pH 7 the model overestimated complexation by both Suwannee River fulvic and humic acids compared with the ion‐exchange measurements. Consistent with the metal internalization step being rate limiting for overall short‐term uptake, intracellular Cd uptake was linear for exposure times less than 20 min at pH 5 or pH 7 for both algal species. After taking into account complexation of Cd in solution, Suwannee River humic substances had no additional effects on cadmium uptake at pH 7, as would be predicted by the free ion model. This absence of effects other than complexation persisted at pH 5, where the tendency of humic substances to adsorb to the algal cell surface is favored. Changes in pH strongly influenced Cd uptake, with the intracellular flux of Cd being at least 20 times lower at pH 5 than at pH 7 for P. subcapitata. Our results support models such as the free ion model or the biotic ligand model, in which humic substances act indirectly on Cd uptake by reducing the bioavailability of Cd by complexation in solution.     

THE INFLUENCE OF pH ON ALGAL CELL MEMBRANE PERMEABILITY AND ITS IMPLICATIONS FOR THE UPTAKE OF LIPOPHILIC METAL COMPLEXES1

Uptake of lipophilic metal complexes by freshwater algae has recently been shown to be pH dependent. Here we look at different physiological aspects that could influence the diffusion of the lipophilic Cd complex, Cd(diethyldithiocarbamate)₂⁰ (Cd(DDC)₂⁰), into algal cells at different exposure pH values. Changes in cell membrane permeability were assessed as a function of pH for three species of green algae [Chlamydomonas reinhardtii P. A. Dang., Pseudokirchneriella subcapitata (Korshikov) Hindák, and Chlorella fusca var. vacuolata Shihira et R. W. Kraus] using two neutral, nonionic probes, fluorescein diacetate (FDA) and D‐sorbitol. In parallel experiments, we exposed algae to inorganic Cd or to Cd(DDC)₂⁰ and monitored Cd intracellular metal distribution, together with phytochelatin synthesis. For the three algal species acclimated at pH 5.5 (w/wo DDC 1 μM) and exposed at this pH, their permeability to FDA and D‐sorbitol was consistently lower than for algae growing at pH 7.0 and exposed at this pH (P < 0.001). The ratio of the FDA hydrolysis rate measured at pH 7.0 with respect to the rate measured at pH 5.5 (both in the presence of DDC) correlated with the ratio of the Cd(DDC)₂⁰ initial internalization rate constant obtained at pH 7.0 versus that obtained at pH 5.5 (three algae species, n = 9, r = 0.85, P = 0.004). Our results strongly suggest that acidification affects metal availability to algae not only by proton inhibition of facilitated metal uptake but also by affecting membrane permeability.     

Growth of Halotolerant Food Spoiling Yeast Debaryomyces nepalensis NCYC 3413 Under the Influence of pH and Salt

Debaryomyces nepalensis, a halotolerant food-spoiling yeast could grow in complex (YEPD) medium at different pHs ranging between 3.0 and 11.0 in the absence of salt and at pH 3.0–9.0 in the presence of different concentrations of NaCl and KCl. The specific growth rate of D. nepalensis was not affected by the initial pH of the medium in the absence of salts, whereas it was affected in the presence of salts. At 2 M NaCl and KCl, the organism exhibited a synergistic effect on pH and salt stress, which was unique in the Debaryomyces species. Irrespective of the initial pH and salt, the intracellular pH of D. nepalensis was ~7.0. Significant organic acid was produced at neutral and alkaline pH and organic acid production increased with the increase in pH and salt. Very specific organic acids are produced in the presence of NaCl and KCl. Our observation would contribute to a better understanding of the physiological phenomenon of halotolerance in D. nepalensis.     

EFFECT OF BUFFERED SOLUTIONS AND SULFATE ON VEGETATIVE AND SEXUAL DEVELOPMENT IN GAMETOPHYTES OF PTERIDIUM AQUILINUM

Experiments were performed to determine effects of buffered solutions (0.01 m ) on vegetative development and fertilization of gametophytes of Pteridium aquilinum. Buffered solutions were used to simulate exposures to acidic precipitation up to 3.5 h. Flagellar movement of sperm was reduced at buffer pH levels below 5.8. Specifically, longevity of motility was reduced so that no movements were observed 8–10 and 5–7 min after exposure to pH 5.6 and 5.2, respectively. Addition of sulfate (86 μm ) depressed the percent motile sperm by 50%, 2–4 min after exposure at all pH values tested. Longevity of flagellar movement was most affected by pH and additions of sulfate. The effect on fertilization was assayed directly by determinations of sporophyte production. Although gametophyte survival and development were not affected by solutions of pH 5.8 to 2.2, fertilization was reduced after exposure to buffers below pH 4.2. Sporophyte production was not altered at pH 5.2 but was reduced 50% at pH levels of 4.2 and 3.2 compared with exposures to pH 5.8. Addition of sulfate (86 μm ) decreased fertilization at least 50% at all pH levels observed. The results suggest that only limited fertilization, and therefore limited genetic recombinations could occur in Pteridium aquilinum under conditions of acidic precipitation (pH and sulfate levels) that prevail in the northeastern United States.     

THE EFFECTS OF PHOSPHITE ON PHOSPHATE STARVATION RESPONSES OF ULVA LACTUCA (ULVALES,CHLOROPHYTA)1

Effects of phosphite (Phi) on phosphate (Pi) starvation responses were determined in Ulva lactuca L. by incubation in Pi‐limited (1 μM NaH₂PO₄) or Pi‐sufficient (100 μM NaH₂PO₄) seawater containing 0–3 mM Phi. Exposure to 1 μM NaH₂PO₄ decreased the growth rate and the content of free Pi and esterified‐P but increased the activities of extracellular alkaline phosphatase (EC 3.1.2.1) and intracellular acid phosphatase (ACP; EC 3.1.2.2); two ACP isozymes observed by activity staining on isoelectric focussing (IEF) gel were induced. The K_m value of Pi uptake rate was decreased by incubation with 1 μM NaH₂PO₄ and the decrease in K_m value was inhibited by 2 mM Phi, reflecting the operation of a high‐affinity Pi uptake system at low Pi concentrations. In the presence of Phi, the growth rate of Pi‐sufficient and Pi‐starved thalli decreased as Phi concentrations were increased from 0 to 2 mM. As Phi concentrations were increased from 0 to 2 mM, the free Pi contents in both Pi‐sufficient and Pi‐starved thalli decreased, but the esterified‐P contents in Pi‐starved thalli increased, whereas those in Pi‐sufficient thalli increased at 1 mM Phi and decreased at 2 mM Phi. Cell wall localized AP activity in both Pi‐sufficient and Pi‐starved thalli decreased as Phi concentrations were increased from 0 to 2 mM. Intracellular ACP activity in Pi‐starved thalli decreased as Phi concentrations were increased from 0 to 2 mM but was not affected in Pi‐sufficient thalli. The induction of ACP isozyme activity and high‐affinity Pi uptake system in Pi‐starved thalli was inhibited by Phi. The present investigation shows that Phi interrupts the sensing mechanisms of U. lactuca to Pi‐limiting conditions.     

pH-dependent modulation of alkaline phosphatase activity in Serratia marcescens

Serratia marcescens is an opportunistic pathogen responsible for causing nosocomial infections, corneal ulcer, necrotizing fasciitis, cellulites, and brain abscess. Alkaline phosphatase (APase) is believed to play an important role in the survival of several intracellular pathogens and their adaptation. We have studied the effect of low phosphate concentration and acid pH on the APase activities of S. marcescens. In a low phosphate medium, some strains of S. marcescens synthesize two different types of APases, a constitutive (CAPase) and an inducible (IAPase). Both the CAPase and IAPase isoenzymes completely lost their enzyme activities at pH 2.3, within 10 min of incubation at 0°C. Acid-treated IAPase isoenzymes I, II, III, and IV solutions when adjusted to pH 7.8 showed recovery of 70%, 52%, 72%, and 60% of the lost activities, respectively. When the pH of the CAPase reaction mixture was raised to pH 7.8, the enzyme activity regained only 5% of its initial activity. Variations in protein concentration also affected the pH-dependent reversible changes of the IAPase activity. The higher the protein concentration, the faster the inactivation of enzyme activity observed at acidic pH at 0°C. Conversely, the lower the protein concentration, the higher the rate of reactivation of enzyme activity observed for IAPase at alkaline pH. Protein interaction studies revealed a lack of similarity between CAPase and IAPase, suggesting separate genetic origin of these potentially virulent genes of S. marcescens. Received: 4 December 2001 / Accepted: 7 January 2002     

Comparison of phosphatase localization in the intraradical hyphae of arbuscular mycorrhizal fungi,Glomus spp. and Gigaspora spp.

The localization of acid and alkaline phosphatases in the intraradical hyphae of the arbuscular mycorrhizal fungi, Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (Gm), Gl. etunicatum Becker and Gerd. (Ge) and Gigaspora rosea Nicol. and Schenck (Gir) were compared. Marigold (Tagetes patula L.) and leek (Allium porrum L.) were inoculated with each of the three fungi. The mycorrhizal roots were harvested at 3, 4, 5 and 6 weeks after sowing (WAS), treated with a digestion solution containing cellulase and pectinase, and then stained for phosphatase activities at pH 5.0 and pH 8.5. The development of fungal structures in the host root was also examined. Gm formed fine-branched (mature) arbuscules only at the early phase of infection (3 to 4 WAS). Mature arbuscules of Ge and Gir were observed from the early phase (4 WAS) up to the end of experiment. At pH 5.0, the localization of the phosphatase activities of the three fungi were similar irrespective to host plant species. The activity appeared in mature arbuscules and intercellular hyphae, whereas the collapsed arbuscules were inactive. Ten millimolar NaF, an acid phosphatase inhibitor, inhibited the phosphatase activities of Gm and Ge but did not affect that of Gir. At pH 8.5, a difference among the fungal species was found in the localization of phosphatase activity while that between host species was not. The mature arbuscules were also the active sites in all three species. Only Gir showed the activity in the intercellular hyphae while the two Glomus spp. did not. Five millimolar EDTA inhibited the activity of Gir at pH 8.5 while the activities of Ge and Gm were not affected by either 5 mM EDTA or 10 mM KCN (both are alkaline phosphatase inhibitors).     

东北丘陵区林地转型耕地对土壤编码碱性磷酸酶基因的细菌群落的影响

【目的】通过研究林地转型耕地对土壤编码碱性磷酸酶基因的细菌群落丰度、多样性和结构的影响,为丘陵区耕地长期施肥下农田土壤微生物多样性丧失的影响机制以及未来的退耕还林过程中土壤微生物多样性的提升和土地可持续利用研究提供一些基础数据和技术支撑。【方法】采用实时荧光定量PCR (real-time quantitative PCR,qPCR)和高通量测序技术解析土壤编码碱性磷酸酶基因的细菌群落的丰度、多样性和结构变化,并耦合土壤化学性质分析,明确土壤编码碱性磷酸酶基因的细菌群落丰度和多样性与土壤化学性质的关系以及关键的驱动因子。【结果】林地垦殖为农田后,长期施肥导致土壤酸化,pH从5.58降至4.72,而土壤速效磷则从2.49 mg/kg增至49.3 mg/kg。相应地,耕地土壤编码碱性磷酸酶基因的细菌群落的丰度和Shannon指数均显著低于林地。基于编码碱性磷酸酶的phoD基因(alkaline phosphatase-encoding gene)序列的物种分类表明,丘陵区土壤编码碱性磷酸酶基因的细菌群落的优势门为变形菌门(Proteobacteria)、蓝藻门(Cyanobacteria)、浮霉菌门(Planctomycetes)、放线菌门(Actinobacteria)、厚壁菌门(Firmicutes)和疣微菌门(Verrucomicrobia),其中林地土壤的蓝藻门的相对丰度显著高于耕地。耕地土壤的慢生根瘤菌属(Bradyrhizobium)和芽孢杆菌属(Bacillus)的相对丰度显著高于林地,而中慢生根瘤菌属(Mesorhizobium)、假单胞菌属(Pseudomonas)、Chlorogloea属、Gemmata属、Phormidesmis属和Pseudolabrys属的相对丰度显著低于林地。土壤编码碱性磷酸酶基因的细菌群落结构因林地转型耕地而发生显著改变。phoD基因丰度和Shannon指数与pH显著正相关,而与总磷、速效磷、硝态氮和铵态氮均显著负相关,其中土壤速效磷是这些影响因素中影响最强烈的,长期施用无机磷肥导致含碱性磷酸酶的土壤细菌群落对有机磷分解的能力退化。【结论】林地转型耕地加之长期施肥改变了土壤pH和速效磷,并在其他理化因子的协同驱动下,导致土壤编码碱性磷酸酶基因的细菌群落丰度、多样性和结构的显著变化。     

DIFFERENTIAL ACTIVITIES OF ACID PHOSPHATASE FROM ADAXIAL AND ABAXIAL REGIONS OF LUPINUS LUTEUS (FABACEAE) COTYLEDONS

Acid phosphatases of abaxial and adaxial regions in the cotyledons of the Lupinus luteus which possess structurally distinct protein bodies were examined. Acid phosphatase activity was investigated by enzyme assays and by gel electrophoresis and was localized by cytochemical methods in the cotyledons of Lupinus luteus L. during germination and seedling development. Acid phosphatase activity was significantly higher in the adaxial (heterogeneous protein body) region as compared to the abaxial (homogeneous protein body) region of the cotyledon. The pH optimum of acid phosphatase from the abaxial region and from the adaxial region was 4.5 and 5.0, respectively. There were significant differences in substrate specificity and isoenzymic composition of the enzyme between the two regions. Isoenzymic composition changed during the course of germination and seedling development. Acid phosphatase was localized in the matrix of the homogeneous protein bodies and in the globoids of the heterogeneous protein bodies at imbibition. After germination (d 3, d 4, d 7) acid phosphatase was localized primarily in the inner cell walls and intercellular spaces of both regions. These results show that different isoenzymes of acid phosphatase show differential localization and the rate of acid phosphatase activation or synthesis differs in cells from the two regions of the cotyledon.     

Resistance to freshwater exposure in White Sea Littorina spp. II: Acid-base regulation

Parameters of acid-base and energy status were studied by in vivo ³¹P-nuclear magnetic resonance spectroscopy in three White Sea Littorina spp. (L.littorea, L. saxatilis and L. obtusata) during prolonged anaerobiosis in freshwater. Intracellular pH decreased significantly, especially during the early period of anaerobiosis, but later the decrease in intracellular pH slowed down considerably, suggesting a capacity for intracellular pH regulation in all three species. There was a trend for intracellular pH to fall most rapidly in the least freshwater-resistant species, L. obtusata, as compared to the most resistant, L. littorea. Non-bicarbonate, non-phosphate buffer values estimated by the homogenate technique were similar in the three studied species (28–37 mmol pH⁻¹ kg⁻¹ wet weight) and did not change during freshwater exposure. The CaCO₃ buffer value of the foot tissues was considerably higher (171–218 mmol pH⁻¹ kg⁻¹ wet weight) and decreased significantly during freshwater exposure. The contribution of the multiple tissue buffering systems to intracellular pH regulation in Littorina spp. shifts between different stages of freshwater exposure. Initially, the non-bicarbonate, non-phosphate tissue buffering system seems to be of major importance for metabolic proton buffering at intracellular pH between 7.5 and 7.0. During later stages of anaerobiosis and at lower intracellular pH, the CaCO₃ buffer is involved in proton buffering. Decrease in the CaCO₃ buffer value during freshwater exposure was in quantitative agreement with the amount of metabolic protons buffered, thus suggesting that CaCO₃ tissue stores may serve as a major buffering system during prolonged anaerobiosis in Littorina spp. Accepted: 23 December 1999     

Participation of the molecular chaperone DnaK in intracellular growth of Brucella suis within U937-derived phagocytes

In the intracellular bacterium Brucella suis, the molecular chaperone DnaK was induced under heat-shock conditions and at low pH. Insertional inactivation of dnaK and dnaJ within the dnaK/J locus led to the conclusion that DnaK, but not DnaJ, was required for growth at 37°C in vitro. Viability of the dnaK null mutant was also greatly affected at low pH. Under conditions allowing intracellular multiplication, the infection of U937-derived phagocytes resulted in long-lasting DnaK induction in the wild-type bacteria. In infection experiments performed with both mutants at the reduced temperature of 30°C, the dnaK mutant of B. suis survived but failed to multiply within U937 cells, whereas the wild-type strain and the dnaJ mutant multiplied normally. Complementation of the dnaK mutant with the cloned dnaK gene restored growth at 37°C, increased resistance to acid pH, and increased intracellular multiplication. This is the first report of the effects of dnaK inactivation in a pathogenic species, and of the temperature-independent contribution of DnaK to intracellular multiplication of the pathogen B. suis.     

THE UPTAKE OF MANNITOL AND SORBITOL BY A SPECIES OF CHLORELLA (CHLOROPHYCEAE)1

Chlorella saccharophila (Krüger) Nadson takes up mannitol and sorbitol in the light and the dark. The rate of uptake is concentration dependent. is not affected by pH in the range pH 6.0 to 8.0 and ii not stimulated by light. Uptake is inhibited by the respiration inhibitor sodium azide (10^-2 M) but not by 3-(3,4-dichlorophenyl)-1,1-di-methyl urea (10^-6 M), an inhibitor of photosynthesis. Sorbitol. but not mannitol, stimulates the rate of dark respiration but both support the heterotrophic growth of the alga. Both compounds permeate the cells of C. miniata. and two strains of C. pyrenoidosa but do not support the heterotrophic growth of these algae. The cells of C. vulgaris are impermeable to both compounds.     

Temperature dependence of intracellular pH: Its role in the conservation of pyruvate apparentKm values of vertebrate lactate dehydrogenases

Summary When apparent Michaelis constants (K _m's) for pyruvate of M₄-lactate dehydrogenases from differently thermally adapted vertebrates are measured at the species' normal cell temperatures, a marked degree of conservation inK _m is observed, but only when the pH of the assay medium is varied in the manner in which intracellular pH varies with temperature in most animals (Fig. 2).K _m measurements performed at a constant pH do not yield this high degree of interspecific conservation inK _m (Figs. 2 and 3).The temperature dependence of intracellular pH preserves the charge states of imidazoles of protein histidines during temperature transitions. Thus under intracellular conditions the ionization state of the active site histidine of LDH will be independent of temperature, reducing the temperature dependence of pyruvate binding. This effect appears important in the contexts of short-term temperature variation experienced by an individual ectotherm and of long-term, evolutionary temperature changes important in speciation processes.These findings emphasize the importance of utilizing biologically realistic pH values in enzyme studies if major adaptive trends are to be observed.     

betaine modulates intracellular thiol and potassium levels in Escherichia coli in medium with high osmolarity and alkaline pH

Glycine betaine stimulates the growth rate of various bacteria in high osmolarity medium. In our studies, glycine betaine stimulated the growth rate of Escherichia coli K 12 in minimal medium with normal osmolarity at alkaline pH (pH 8.2). Betaine also caused a reduction in the intracellular pools of K⁺ and low molecular weight thiols in E. coli growing both in medium with high osmolarity and at alkaline pH. These effects of betaine were absent at pH 7.0. In cells growing in high osmolarity medium, 10 mM sodium acetate or 10 M N-ethylmaleimide reduced expression of the osmosensitive gene proU to the same extent as treatment with betaine; however, under these conditions, sodium acetate and N-ethylmaleimide did not stimulate the growth of E. coli. It is proposed that low molecular weight thiols and intracellular pH may participate in the response of E. coli to betaine.     

塞北荒漠草原柠条锦鸡儿AM真菌的空间分布

为了探明塞北荒漠草原AM真菌生态分布规律,于2013年6月选取河北沽源县二牛点、内蒙古上都镇和青格勒图嘎查3个样地,按照0—10 cm、10—20 cm、20—30 cm、30—40 cm、40—50 cm 5个土层分别采集柠条锦鸡儿(Caragana korshinskii)根围土壤样品,研究了AM真菌空间分布特征及其与土壤因子的相关性。结果表明,柠条锦鸡儿根系能与AM真菌共生形成疆南星型丛枝菌根,AM真菌孢子密度和定殖率与样地和采样深度密切相关。二牛点孢子密度最大,3个样地孢子密度最大值均在0—10 cm土层,并随土层加深而减少;3个样地菌丝定殖率依次为上都镇青格勒图嘎查二牛点,峰值均在0—10 cm土层;泡囊定殖率青格勒图嘎查显著低于其他样地,但土层间无规律性变化;丛枝样地间定殖状况差异明显,变化趋势为青格勒图嘎查上都镇二牛点;AM真菌总定殖率和定殖强度最大值在上都镇。孢子密度与土壤有机C、全N、易提取球囊霉素和总球囊霉素极显著正相关,与p H值显著正相关,与速效P显著负相关;菌丝定殖率与土壤p H值、速效P、全N和酸性磷酸酶显著负相关;泡囊和丛枝定殖率与土壤碱解N和碱性磷酸酶具有极显著相关性;总球囊霉素和易提取球囊霉素与脲酶显著正相关,与碱解N、全N、碱性磷酸酶和酸性磷酸酶极显著正相关。主成分分析表明,酸性磷酸酶、总球囊霉素、全N、碱性磷酸酶、有机C是影响荒漠土壤营养状况的主要因子。总球囊霉素和易提取球囊霉素平均含量分别为3.19 mg/g和1.17 mg/g,占土壤有机C平均含量比为7.77%和3.83%,占土壤全N平均含量比为20.81%和9.57%。多元线性回归表明,总球囊霉素和易提取球囊霉素与土壤有机C和全N具有显著线性相关关系。研究球囊霉素与土壤有机C和N的比例关系可进一步明确AM真菌的生态功能,对荒漠土壤C库和N库研究具有重要意义。     

Effects of Pseudomonas fluorescens F113 on Ecological Functions in the Pea Rhizosphere Are Dependent on pH

Abstract The aim of this microcosm study was to determine influence of the antibiotic 2,4-diacetylphloroglucinol (DAPG) on the effect of wild-type and functionally modified Pseudomonas fluorescens F113 strains in a sandy loam soil of pH 5.4 planted with pea (Pisum sativum var Montana). The functional modification of strain F113 was a repressed production of DAPG, useful in plant disease control, creating the DAPG negative strain F113 G22; both were marked with a lacZY gene cassette. Lowering the soil pH to 4.4 significantly reduced the plant shoot and root weights and the root length, whereas the bacterial inocula had no significant effect. Both inocula significantly reduced the shoot/root ratio at pH 5.4, but this effect was not evident at the lowered or elevated (6.4) pH levels. The decrease in pH significantly increased the fungal and yeast colony-forming units from the rhizosphere (root extract), but did not affect the total bacterial c.f.u.'s. Inoculatioin with strain F113 in the pH 4.4 soil resulted in a significantly greater total bacterial population. The fungal and yeast c.f.u.'s were not significantly affected by the inocula at any pH studied. Increasing the pH significantly increased the indigenous Pseudomonas population in comparison to the reduced pH treatment and significantly increased both the introduced and total Pseudomonas populations. The antibiotic producing strain significantly reduced the total bacterial population and the NAGase activity (related to fungal activity) at pH 6.4 where the inocula population was the greatest. Alkaline phosphatase, phosphodiesterase, aryl sulfatase, β-glucosidase, alkaline β-galactosidase, and NAGase activities significantly increased with increasing in pH. The F113 inocula reduced the acid phosphatase activity at pH 5.4 and increased the acid β-galactosidase activity over all the pH treatments. The results presented illustrate the variation in impact with soil pH, with implications for variability in efficacy of Pseudomonas fluorescens biocontrol agents with soil pH. Received: 26 June 1998; Accepted: 1 February 1999     

Occurrence and expression of acid phosphatase of Hymenoscyphus ericae (Read) Korf & Kernan,in isolation or associated with plant roots

Summary The activity of acid phosphatase produced in pure culture by the endomycorrhizal fungus Hymenoscyphus ericae (Read) Korf & Kernan (H. ericae LPA 2) was inhibited by high phosphorus levels, alkaline pH, fluoride, molybdate and mannosidase, and activated by concanavalin A. Over 80% of the enzyme activity was due to two wall-bound acid phosphatase isozymes with the characteristics of mannose-rich glycoproteins. Antiserum was raised against the major, low-molecular-weight wall isozyme and its activity tested by immunoblotting and ELISA. The antiserum cross reacted 100% with exocellular (excreted) and 28% with cytoplasmic cellular fractions of H. ericae (LPA 2) cultures, and showed high reactivity with other strains of H. ericae but not with fungal isolates from Erica hispidula L. or E. mauritanica L. Ultrastructural localization of acid phosphatase by cytoenzymology and indirect immunogold labelling confirmed its association with the fungal wall in pure culture and showed that the influence of a high phosphorus level, fluoride and molybdate is through inactivation of the enzyme. Intense acid phosphatase activity, sensitive to the latter inhibitors, was also present on external hyphae growing over a host or non-host root but it was weak or absent from intracellular hyphae where these developed within a host root. Indirect immunolabelling confirmed that this acid phosphatase was of fungal origin and that the specific inhibitory effect of host cells is due to inactivation of the enzyme rather than repression of its synthesis. Possible implications of fungal acid phosphatase in ericoid endomycorrhizal infection processes are discussed together with mechanisms that may be regulating the enzyme activity.