High Acid Phosphatase Activity Research Articles

The role of macrophages in the disappearance of Meckel’s cartilage during mandibular development in mice

Meckel’s cartilage is a supporting tissue in the embryonic mandible that disappears during development; however, the precise mechanisms of this disappearance process are still undetermined. In this study, we observed morphological changes of Meckel’s cartilage with development and analyzed the factors which might be related to this process. Meckel's cartilage of ICR strain mice from 14 to 19 days gestation (E14–19) were used in this study. Histological and immunohistochemical studies indicated the decrease in the amount of sulfated glycoconjugates and the localization of type I collagen in the Meckel's cartilage matrix during development. Chondrocytes also expressed high acid phosphatase activities at these stages. An organ culture study indicated that Meckel's cartilage at E17 disappeared during the cultivation period, while the cartilage at E14 did not disappear. Massive penetration of macrophages into the perichondrium was detected at E16. RT-PCR analysis of Meckel's cartilage indicated the expression of interleukin-1β, type I collagen, MMP-9 at E17, but not at E14. MIP-1α, the candidate molecule for macrophage chemoattractant factor, was expressed at E14. These results indicated the dynamic matrix changes of Meckel's cartilage during development and suggested that the functional changes of chondrocytes in synthesis of type I collagen might be induced by interleukin-1β secreted by the penetrating macrophages.

IMPACTO DEL NITRÓGENO SOBRE EL ESTADO NUTRICIONAL DEL FÓSFORO Y SU PRINCIPAL BIOINDICADOR: RESPUESTA EN RAÍCES Y HOJAS DE PLANTAS DE FRIJOL EJOTERO

The objective of the present work was to determine the effect of different doses of nitrogen (N) on the nutritional status of phosphorus (P) in roots and leaves of green bean plants (Phaseolus vulgaris L. cv. Strike), and also to examine the response of acidphosphatase activity as the main bioindicator of P. Nitrogen was applied to the nutrient solution as NH4NO3 and increasing doses of: N1 = 1.5 mM, N2 = 3.0 mM, N3 = 6.0 mM, N4 = 12.0 mM, N5 = 18.0 mM, and N6 = 24.0 mM of N were added. The results indicate that both deficient and toxic N doses were characterized by the lowest level of total, inorganic and organic phosphorus, as well as the highest activity of acid phosphatase; these effects are due to the direct influence between N and P levels. Treatment N4 presents the highest levels of the diverse fractions of P and the lowest activity of acid phosphatase. Additionally, it was found that the highest proportion of P in roots and leaves are in the forms of P-inorganic (Pi) and P-organic. These represented more than 65 % of total P, so it can be said that they represent the main forms of phosphorus in green bean plants. Finally, it should be noted that acid phosphatase activity was significantly correlated with Pi, which indicates that it can be used as a good indicator of the nutritional status of P in the roots and leaves of green bean plants.

Platelet‐activating factor receptor (PAFR) lysosomal targeting is mediated by p85α subunit of PI3K in enterocytes

PAFR signals via the PI3K pathway to regulate apoptosis in rat small intestinal epithelial cells (IEC‐6). In IEC‐6, over‐expressed p85α regulatory subunit of PI3K and PAFR directly interact with each other and co‐localize to perinuclear vesicles resulting in diminished PAF‐induced apoptosis. We hypothesized that p85α regulates PAFR trafficking and function through lysosomal targeting. Immunostaining revealed that over‐expressed p85α co‐localized with lysosomal associated protein1 (LAMP1) and over‐expressed PAFR. In p85α over‐expressing cells we observed a 2‐fold increase of acid phosphatase (AP) activity in LAMP1‐ and p85α‐positive sucrose gradient fractions. In HT29 colonic epithelial cells, native PAFR was internalized upon 10 to 20 mins of PAF exposure, interacted with native p85α, then recycled to the cell surface following prolonged PAF exposure (40 min). Over‐expressed p85α in HT‐29 reduced the baseline membrane expression of PAFR and upon PAF stimulation, delayed the recycling of PAFR to the surface. Immunoblotting analysis of sucrose gradient fractions from p85α over‐expressing HT‐29 cells revealed that native PAFR was present in p85α‐and LAMP1‐positive fractions that had the highest AP activity. In summary, the inhibition of PAFR signaling by p85α over‐expression is due to removal of receptors from the cell surface, and targeting to lysosomes. Supported by NIH HD37581 and DK062960.

Lyophilized, non-viable, recombinant E. coli cells for cadmium bioprecipitation and recovery

The phoN gene, encoding a non-specific acid phosphatase from Salmonella enterica sv. Typhi, was cloned and overexpressed into Escherichia coli. The E. coli cells bearing phoN showed high acid phosphatase activity and removed 83% of cadmium from a 1 mM solution in 3 h, when provided with 5 mM β-glycerophosphate as a source of phosphate. Such cells, when lyophilized without any lyo/cryoprotectant, were rendered non-viable but fully retained cadmium precipitation ability. Lyophilized recombinant cells could be stored at room temperature, without significant loss of activity for up to 6 months, and removed upto 21 g cadmium/g dry weight. The precipitated cadmium could be easily recovered from the cells by dilute acid wash, following which the cells retained their cadmium precipitation ability, facilitating their reuse. The use of genetically engineered, non-viable E. coli cells offers an environmentally safe biotechnology for bioremediation of cadmium from contaminated sites.

Atividade de fosfatases em gramíneas forrageiras em resposta à disponibilidade de fósforo no solo e à altura de corte das plantas

A eficiência de utilização de um nutriente, expressa pela relação entre a biomassa produzida e a quantidade absorvida, é uma importante característica adaptativa das plantas, particularmente daquelas cultivadas em solos com baixa disponibilidade desse nutriente. Maior eficiência de utilização de P (EUP) é conferida pela maior taxa de remobilização de P, que consiste na translocação desse nutriente para regiões de maior demanda metabólica na planta. Maiores taxas de remobilização têm sido associadas a maiores atividades das enzimas: fosfatase ácida (APase) e ribonuclease (RNase). Neste trabalho, avaliou-se a atividade dessas enzimas em plantas de Brachiaria decumbens, pouco exigente, e de Panicum maximum cv. Tanzânia, mais exigente em P, cultivadas em solos que receberam diferentes doses desse nutriente e submetidas a diferentes alturas de corte. O ensaio foi realizado em casa de vegetação, utilizando amostra do horizonte B de um Latossolo Vermelho-Amarelo argiloso. Os tratamentos resultaram da combinação fatorial das duas gramíneas, das doses de 100, 200 e 500 mg dm-3 de P e das três alturas de corte: sem corte e corte a 15 e 30 cm a partir da superfície do solo para Brachiaria; e sem corte e corte a 20 e 40 cm para Panicum. As unidades experimentais consistiram de vasos com 10 dm³ de solo, com 10 plantas. Os resultados indicaram que não houve diferença significativa na produção de biomassa das duas gramíneas, mas a adição de P propiciou maior produção e maior teor desse nutriente na parte aérea de ambas. As plantas submetidas a cortes mais severos apresentaram menor produção e maiores teores de P na parte aérea. Ocorreu efeito negativo das doses de P na atividade da APase e da RNase nas duas forrageiras. As plantas cultivadas com a menor dose de P apresentaram maior atividade dessas enzimas e maior EUP. A atividade de ambas as fosfatases decresceu com a idade das plantas. No tratamento com o corte mais intenso, independentemente da dose de P, tanto Brachiaria quanto Panicum apresentaram menor EUP. Isso ocorreu associado à maior atividade das enzimas APase e RNase, indicando que outros mecanismos relacionados com a adaptação das plantas a baixas disponibilidades de P podem estar envolvidos.

Effect of microbial inoculation during vermicomposting of different organic substrates on microbial status and quantification and documentation of acid phosphatase

In this experiment, three microbial strains were inoculated in two different organic wastes to study their effect on the humic acids content, acid phosphatase activity and microbial properties of the final stabilized products. Pyrophosphate extract of vermicomposts were analyzed through polyacrylamide gel electrophoresis to study the nature of a isozymes in different treatments. Results suggested that vermicomposting increased humic acids content and acid phosphatase activity in organic substrates and microbial inoculation further enhanced the rate of humification and enzyme activity. Although humic acids content in different microorganism-inoculated vermicomposts were statistically at par, acid phosphatase activity in these treatments was significantly (P<0.05) different. Results revealed that microbial respiration was increased due to vermicomposting, but a reduction in microbial biomass was recorded after stabilization of organic wastes. Although vermicomposting increased the value of microbial quotient (qCO(2)), microbial inoculation did not show any significant effect on qCO(2). The zymogram revealed that two isozymes of acid phosphatase (group II and group III) were present in all vermicompost samples and higher acid phosphatase activity in fungi-inoculated vermicomposts might be due to the presence of an additional isozyme (group I) of acid phosphatase.

Rhizodeposition of Zea mays L. as affected by heterosis

The objective of the present work was to investigate in a field experiment the quantity and quality of rhizodeposits of different parental inbred lines (Lo1016 and Lo964, B73 and H99) and hybrids of Zea mays L. Rhizosphere soil was collected after 40 days and several properties were determined: pH, organic carbon, total nitrogen, acid and alkaline phosphatases, organic acids, bioavailable phosphorous, α-amino nitrogen, total phenols, total root-derived rhizodeposits. The results showed that heterosis induced more qualitative differences within the genotypes as δ13C, TOC and TN did not show any significant differences. The two groups of genotypes enhance phosphorous availability adopting two different strategies. In the first group, B73 × H99 shows the best phenological performance as well as the highest concentration of bioavailable P, result which is correlated with a high organic acid concentration (in particular succinic and acetic acid), total phenols, α-amino nitrogen and acid phosphatase activity. There is thus a strict relationship between the phenological superiority of this particular hybrid and its ability to modify the chemistry of its rhizosphere whereas the second hybrid (Lo1016 × Lo964) seems to have developed different strategies as for example changing the root morphology, stimulating microbial biomass or favouring mycorrhizal symbiosis.

Isolation and biochemical characteristics of a molecular form of epididymal acid phosphatase of boar seminal plasma

The fluid of boar epididymis is characterized by a high activity of acid phosphatase (AcP), which occurs in three molecular forms. An efficient procedure was developed for the purification of a molecular form of epididymal acid phosphatase from boar seminal plasma. We focused on the epididymal molecular form, which displayed the highest electrophoretic mobility. The purification procedure (dialysis, ion exchange chromatography, affinity chromatography and hydroxyapatite chromatography) used in this study gave more than 7000-fold purification of the enzyme with a yield of 50%. The purified enzyme was homogeneous by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The purified molecular form of the enzyme is a thermostable 50 kDa glycoprotein, with a pI value of 7.1 and was highly resistant to inhibitors of acid phosphatase when p-nitrophenyl phosphate was used as the substrate. Hydrolysis of p-nitrophenyl phosphate by the purified enzyme was maximally active at pH of 4.3; however, high catalytic activity of the enzyme was within the pH range of 3.5–7.0. Kinetic analysis revealed that the purified enzyme exhibited affinity for phosphotyrosine ( K m = 2.1 × 10 −3 M) and was inhibited, to some extent, by sodium orthovanadate, a phosphotyrosine phosphatase inhibitor. The N-terminal amino acid sequence of boar epididymal acid phosphatase is ELRFVTLVFR, which showed 90% homology with the sequence of human, mouse or rat prostatic acid phosphatase. The purification procedure described allows the identification of the specific biochemical properties of a molecular form of epididymal acid phosphatase, which plays an important role in the boar epididymis.

Root processes influencing phosphorus availability in volcanic soils under youngPinus radiataplantations

Phosphorus (P) availability was investigated in rhizosphere soils under 4- to 5-year-old, second-rotation Pinus radiata D. Don and understorey grass (browntop, Agrostis capillaris L.) in two P-deficient Andosols (a Pumice Soil and an Allophanic Soil). Pinus radiata rhizosphere had more soil organic matter, greater mycorrhizal hyphal length density, higher acid phosphatase activity, and more concentrated dissolved organic carbon than bulk soil or the rhizosphere of grass species in one or both soils. Concentrations of resin P and organic P in the P. radiata rhizosphere were higher than those in the grass rhizosphere and bulk soils, suggesting that P. radiata rhizosphere processes have a greater potential to accumulate organic P and mobilize soil P than understorey grass rhizosphere processes. This effect was less marked in the Allophanic Soil than in the Pumice Soil, probably because of the higher P-fixing capacity and lower plant-available P concentrations in the Allophanic Soil.

Soil Phosphorus Uptake by Continuously Cropped Lupinus albus: A New Microcosm Design

When grown in soils with sparingly available phosphorus (P), white lupin (Lupinus albus L.) forms special root structures, called cluster roots, which secrete large amounts of organic acids and concomitantly acidify the rhizosphere. Many studies dealing with the understanding of this P acquisition strategy have been performed in short time experiments either in hydroponic cultures or in small microcosm designs with sand or sand:soil mixtures. In the present study, we applied an experimental design which came nearer to the natural field conditions: we performed a one-year experiment on large microcosms containing 7 kg of soil and allowing separation of rhizosphere soil and bulk soil. We planted six successive generations of lupins and analysed P uptake, organic P desorption, phosphatase activities and organic acid concentrations in different soil samples along a spatio-temporal gradient. We compared the rhizosphere soil samples of cluster (RSC) and non-cluster roots (RSNC) as well as the bulk soil (BS) samples. A total shoot biomass of 55.69 ± 1.51 g (d.w.) y−1 was produced and P uptake reached 220.59 ± 5.99 mg y−1. More P was desorbed from RSC than from RSNC or BS (P < 0.05). RSC and RSNC showed a higher activity of acid and alkaline phosphatases than BS samples and a higher acid phosphatase activity was observed in RSC than in RSNC throughout the one-year experiment. Fumarate was the most abundant organic acid in all rhizosphere soil samples. Citrate was only present in detectable amounts in RSC while malate and fumarate were recovered from both RSC and RSNC. Almost no organic acids could be detected in the BS samples. Our results demonstrated that over a one-year cultivation period in the absence of an external P supply, white lupin was able to acquire phosphate from the soil and that the processes leading to this P uptake took place preferentially in the rhizosphere of cluster roots.

Improved phosphorus acquisition and biomass production in Arabidopsis by transgenic expression of a purple acid phosphatase gene from M. truncatula

Phosphorus (P) is one of the least-available nutrients in soils; improvement in plant P acquisition will significantly impact agriculture and the environment. A purple acid phosphatase ( MtPAP1) cDNA was isolated from the model legume Medicago truncatula. During growth in high-phosphate conditions, MtPAP1 transcripts were highest in leaves, while under low-phosphate conditions, MtPAP1 transcript levels were reduced in leaves and increased significantly in roots. Three chimeric gene constructs were made in which the MtPAP1 was either driven by the root-specific MtPT1 promoter or by the constitutive CaMV35S promoter. The constructs also included either the native signal sequence of MtPAP1 or a patatin signal sequence from potato. Transgenic Arabidopsis plants carrying the chimeric MtPAP1 gene constructs showed 4.6- to 9.9-fold higher acid phosphatase activities in the root apoplast relative to the control plants. The increase in enzyme activity correlated closely with the expression levels of the transgenes. Highly expressed transgenic lines were chosen for each construct and used for further analyses. The expressed acid phosphatase was secreted into the rhizosphere as shown by enzyme activity staining and HPLC analysis of organic P degradation in liquid culture. Compared with empty vector control, all the tested transgenic lines showed a minimum of a two-fold increase in biomass production and total phosphorus content after about 1 month growth when 2 mM phytate was supplied as the sole source of phosphorus. The results clearly demonstrate that overexpression of plant acid phosphatase gene is an effective approach to improve organic phosphorus acquisition.

Indicadores biológicos associados ao ciclo do fósforo em solos de Cerrado sob plantio direto e plantio convencional

O objetivo deste trabalho foi avaliar a influência do plantio direto, do preparo convencional do solo e de plantas de cobertura sobre indicadores biológicos associados ao ciclo do fósforo (P). O trabalho foi realizado em três áreas adjacentes, num Latossolo Vermelho-Amarelo, distribuídas da seguinte maneira: área I, dois anos de experimentação, comparando esses sistemas de plantio; área II, seis anos de experimentação e área III, Cerrado nativo. Em julho/1998 e janeiro/1999, avaliaram-se: o P da biomassa, populações de fungos e bactérias totais e solubilizadores de fosfato e a atividade da fosfatase ácida, nas profundidades de 0-5 e de 5-20 cm. A atividade da fosfatase e a ocorrência de fungos e bactérias solubilizadoras nas áreas com plantio direto foram significativamente superiores às das áreas com plantio convencional, na profundidade de 0-5 cm. O tempo de implantação acentuou as diferenças entre plantio direto e convencional quanto aos indicadores avaliados. O P da biomassa diminuiu no tratamento plantio direto com nabo forrageiro (Raphanus sativus) da área II. Os fungos solubilizadores aumentaram na presença de guandu (Cajanus cajan) e nabo forrageiro, e as bactérias solubilizadoras aumentaram na presença de guandu. O solo sob vegetação nativa apresentou maior atividade da fosfatase em relação ao das áreas cultivadas, evidenciando a importância da mineralização do P orgânico nesse ecossistema.

Fosfatases na dinâmica do fósforo do solo sob culturas de cobertura com espécies micorrízicas e não micorrízicas

O objetivo deste trabalho foi avaliar, mediante a atividade de fosfatases no solo, o efeito de plantas de cobertura micorrízicas e não micorrízicas nos aspectos biológicos da dinâmica do fósforo em sistemas sob plantio direto. Solos sob espécies não micorrízicas apresentaram maior atividade de fosfatases ácidas e alcalinas no estádio de floração, e os níveis de atividade de fosfatases ácidas persistiram nos cultivos subseqüentes ao crescimento das culturas de cobertura. A maior atividade enzimática, relacionada à mineralização de fosfatos orgânicos, em solos com espécies não micorrízicas pode ser um mecanismo de aumento da mobilização do fósforo no solo, compensando a ausência de micorrizas.

Root traits as tools for creating phosphorus efficient crop varieties

This paper provides a brief assessment of the genetic variation in root properties (root morphology, including root hairs), mycorrhizal symbiosis, uptake kinetics parameters and root-induced changes (pH, organic acids and acid phosphatase) in the rhizosphere of various crop species and their genotypes and then briefly discusses the opportunities and challenges of using such knowledge for enhancing P efficiency of future crop genotypes by genetic means. Wide genotypic variation and heritability of root morphology, root hair length and density and thereby P acquisition provide opportunities for selection and breeding for root characteristics for increasing P acquisition. The progress is challenged by the concerns of high carbon cost of larger root systems and by the lack of cost effective methods to determine root length of a large number of genotypes under field conditions. The carbon cost of root hairs is low. Furthermore, low cost methods now exist to compare root hair formation of field grown genotypes. The development and application of sophisticated methods has advanced our knowledge on the role of mycorrhizal symbiosis in P acquisition and also on the molecular basis of fungi and plant interactions. However, extensive studies to explore genotypic variation in mycorrhizal responsiveness are rare, which makes it difficult to assess, how mycorrhizal symbiosis can be manipulated through breeding efforts. The promising variation found in P uptake kinetics parameters of crop genotypes in few studies indicates that more genotypes may be screened by relatively simple nutrient solution culture techniques. The genetic manipulation of the overall differences in cation-anion uptake, which is the main cause of rhizosphere pH change, may be difficult. For manipulation of rhizosphere pH, agronomic measures such as applications of ammonium or nitrate fertilisers may be more useful than breeding approaches. Also it seems difficult to assess what kind of genetic analysis should be performed to support the breeding efforts. Phosphorus mobilisation effect of pH depends on soil P compounds, therefore will differ with soil type. Both the enhanced release of organic acids and higher acid phosphatase activity in the rhizosphere may be useful for increasing P acquisition from inorganic and organic P pools, respectively. Modification of these traits by genetic means should be considered. For successful breeding programmes, the role of various root traits needs to be targeted in an integrated manner and then methods need to be developed for studying their importance under natural soil conditions, so that the genotypic variation can be explored and their ecological significance in P acquisition can be established.

Acid phosphatase activity and leaf phosphorus content in soybean cultivars

The phosphate fertilization represents the most costly fraction of soybean crop production. Efficient soybean cultivars for P absorption and utilization in soils of medium available P are highly desirable and might contribute for increasing crop production potential. Thirty two soybean [Glycine max (L.) Merr.] cultivars recommended for 'Cerrado' and differing in growth cycle (early, semi-early, semi-late, and late) were grown in a dystrophic Typic Haplustox Cerrado soil to evaluate the acid phosphatase activity, P content in the diagnostic leaf, and shoot biomass. There were differences among the soybean cultivars within all maturation groups in acid phosphatase activity and shoot biomass. The diagnostic-leaf P-content showed significant differences on semi-late and late maturation groups' cultivars. The acid phosphatase activity correlated positively with the plant shoot biomass from semi-early (r = 0.46) and late (r = 0.47) cultivars, and negatively (r = -0.40) with the P content in the diagnostic leaf of late maturation cultivars. The occurrence of soybean cultivars with high and low acid phosphatase activity within the same maturation groups indicates the existence of different mechanisms involving P mobilization in the soil and internal plant P remobilization.

Changes in the carbon metabolism in nitrophenolgrown cultures of Nostoc linckia and Scenedesmus bijugatus, isolated from rice soil

The response of photosynthetic metabolism of carbon towards nitrophenol treatment in cultures of Nostoc linckia and Scenedesmus bijugatus was assessed by examining the cellular contents and activities of the enzymes. The starch content and non-reducing sugars were significantly lower in nitrophenol-grown cultures. The alterations were marked in activities of the enzymes involved in starch metabolism. The enhancement in the activity of phosphorylase clearly supports the observed reduction in accumulation of both starch as well als non-reducing sugars. The decreased activities of fructose 1,6-biphosphatase and sucrose phosphate synthase, and the enhanced activity of invertase resulted in low level accumulation of non-reducing sugars. The observed high activity of acid phosphatase resulted in concomitant decrease in levels of starch.

Histopathologic and histochemical biomarker responses of Baltic clam, Macoma balthica, to contaminated Sydney Harbour sediment, Nova Scotia, Canada.

Sediments in Sydney Harbour, Nova Scotia, are highly contaminated by polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and heavy metals. Histopathologic and histochemical evaluations were made on the Baltic clam, Macoma balthica, exposed to 11 Sydney Harbour sediment samples. Histologic lesions in digestive gland (tubular dilation or atrophy, macrophage aggregates, tubular cell necrosis, and tissue inflammation) and gonads (macrophage aggregates, supporting cell, germ cell, and ovarian cell necroses) were frequently detected in clams exposed to the most contaminated sediments from the harbor. Clams exposed to these contaminated sediments also had the highest acid phosphatase activity. The average scores of tubular dilation or atrophy, ovarian cell necrosis, and the sums of mean digestive gland lesions correlated significantly with sediment PCBs, and the activities of acid phosphatase correlated significantly with sediment heavy metals, PAHs, and PCBs. Among the lesions, digestive gland tubular dilation or atrophy, tubular cell, germ cell, and ovarian cell necroses, and the activity of acid phosphatase are the best sublethal effect indicators in Macoma exposed to Sydney Harbour sediments. Key words: biomarkers, chronic biologic effects, clams, histology, histochemistry, Macoma balthica, marine sediment, polynuclear aromatic hydrocarbons, polychlorinated biphenyls.

Histochemical and ultrastructural studies of cartilage resorption and acid phosphatase activity during antler growth in fallow deer (Dama dama).

Cartilage resorption in forming primary fallow deer antlers was studied by histochemistry and electron microscopy. A high activity of tartrate-resistant acid phosphatase (TRAP), a histochemical marker of skeletal resorbing cells, was first detected in cells located in the mesenchymal tissue separating the columns of hypertrophic cartilage. No cartilage resorption was observed in this region. Intense TRAP staining occurred in large multinucleated cells (identified as inactive osteoclasts) as well as in smaller cells (regarded as mononuclear osteoclast progenitors). On the basis of these findings it was concluded that this was the region where osteoclasts differentiated from progenitor cells. Further proximally, the mineralized cartilage was eroded by active osteoclasts that were located in Howship's lacunae and exhibited an intense TRAP staining. Electron microscopy showed that the cells identified as inactive osteoclasts lacked a polarized organization. In contrast, the active osteoclasts in the zone of cartilage resorption exhibited a typical polarized organization: the nuclei congregated near the basolateral cell surface, and there was a zone of deep membrane infoldings (ruffled border) surrounded by a clear zone at the apical cell pole adjacent to the resorption surface of the mineralized cartilage. The multinucleated cartilage-resorbing cells of the forming antler thus exhibited the typical histochemical and morphological features of active mammalian osteoclasts. Low levels of TRAP activity were also observed in hypertrophic chondrocytes; however, the specificity and potential significance of this staining remain to be elucidated.

Arbuscular mycorrhizal fungi respond to the substrate pH of their extraradical mycelium by altered growth and root colonization.

• To test the response of arbuscular mycorrhizal (AM) fungi to a difference in soil pH, the extraradical mycelium of Scutellospora calospora or Glomus intraradices, in association with Plantago lanceolata, was exposed to two different pH treatments, while the root substrate pH was left unchanged. • Seedlings of P. lanceolata, colonized by one or other of the fungal symbionts, and nonmycorrhizal controls, were grown in mesh bags placed in pots containing pH-buffered sand (pH around 5 or 6). The systems were harvested at approximately 2-wk intervals between 20 and 80d. • Both fungi formed more extraradical mycelium at the higher pH. Glomus intraradices formed almost no detectable extraradical mycelium at lower pH. The extraradical mycelium of S. calospora had higher acid phosphatase activity than that of G. intraradices. Total AM root colonization decreased for both fungi at the higher pH, and high pH also reduced arbuscule and vesicle formation in G. intraradices. • In conclusion, soil pH influences AM root colonization as well as the growth and phosphatase activities of extraradical mycelium, although the two fungi responded differently.

GROWTH AND METABOLISM OF CUCUMBER IN PHOSPHATE-DEFICIENT CONDITIONS

The influence of phosphate deficiency on the growth, phosphatase activity, CO2 exchange, and sugar accumulation in the leaves and roots of cucumber (Cucumis sativus L.) was studied during 4 weeks of plant culture. The growth on nutrient medium without phosphate decreased Pi (inorganic orthophosphate) content in leaves and roots of plants to about 10% of control. Phosphate starvation significantly decreased growth of shoots and mass of roots, whereas root elongation growth was enhanced (diameter of root decreased). Intensity of root elongation was most pronounced at the beginning of culture on P-deficient medium and remained similar even after transfer to full nutrient medium. Phosphate-deficient cucumber plants had higher acid phosphatase activity both in extracts from roots and leaves and in root exudates when compared to samples from phosphate-sufficient plants. Photosynthesis rate was not affected at the beginning of culture but decreased significantly in leaves of 36-day-old −P (phosphate-deficient) plants. Reducing sugars and sucrose content increased in all tissues of phosphate-deficient plants as compared to control plants but only at a moderate stage of phosphate deficiency (24-day-old plants). Carbohydrate content declined during the subsequent week of growth, possibly because of inhibitory effects of advanced phosphate deficiency on photosynthesis and sugar production.