Calcium is essential for fructan synthesis induction mediated by sucrose in wheat

The role of Ca²⁺ in the induction of enzymes involved in fructan synthesis (FSS) mediated by sucrose was studied in wheat (Triticum aestivum). Increase of FSS enzyme activity and induction of the expression of their coding genes by sucrose were inhibited in leaf blades treated with chelating agents (EDTA, EGTA and BAPTA). Ca²⁺ channel blockers (lanthanum chloride and ruthenium red) also inhibited the FSS response to sucrose, suggesting the participation of Ca²⁺ from both extra- and intra- cellular stores. Sucrose induced a rapid Ca²⁺ influx into the cytosol in wheat leaf and root tissues, shown with the Ca²⁺ sensitive fluorescent probe Fluo-3/AM ester. Our results support the hypothesis that calcium is a component of the sucrose signaling pathway that leads to the induction of fructan synthesis.     

Acid phosphatase activity may affect the tuber swelling by partially regulating sucrose-mediated sugar resorption in potato

APase activity is involved in regulating many physiological and developmental events by affecting the resorption process.In this study, we investigate the role of APase activity in tuber development in potato. APase activities were mainly localized in cytoplasm, gaps among cells and stroma of amyloplasts of parenchyma cells at the stage of tuber swelling. AP1, encoding a putative APase, was also highly expressed in swelling tubers and a low level of expression was observed in elongated stolons and matured tubers. Inhibition of APase activity by applying Brefeldin A, an inhibitor of APase production and secretion, significantly suppressed the tuber swelling and moderately affected the stolon elongation and the tuberization frequency. During tuber development, sucrose serves as the main soluble sugar for long-distance transportation and resorption. Moreover, Inhibition of APase activity by Brefeldin A markedly reduced the sucrose content in tubers and further decreased the starch accumulation, suggesting that the function of APase in regulating the tuber swelling might be at least artially mediated by the sugar resorption. Exogenous sucrose treatments further indicate the important role of sucrose-mediated sugar resorption in tuber swelling. These results suggest that the APase activity might affect the tuber swelling by partially regulating the sucrose-mediated sugar resorption.     

Protein tyrosine phosphatase activity is required for IL-4 induction of IL-4 receptor alpha-chain

To investigate the role of protein tyrosine phosphatases in IL-4Ralpha-chain expression and signaling, we first established that SHP-1, but not SHP-2, coimmunoprecipitated with anti-IL-4Ralpha chain Abs in extracts prepared from resting lymphocytes. We further observed that the protein tyrosine phosphatase inhibitors Na3VO4 and pervanadate blocked the striking induction of IL-4Ralpha-chain expression that is mediated by IL-4. However, Na3VO4 did not diminish IL-4-induced Stat6 phosphorylation nor did it block the IL-4-mediated increase in IL-4Ralpha-chain mRNA. The striking inhibition in total cellular IL-4Ralpha-chain and in cell surface IL-4 receptors was associated with an inhibition of biosynthetic labeling of IL-4Ralpha-chain after a 30- min pulse with [35S] methionine, indicating that reduction of IL-4Ralpha-chain protein resulted from either a diminished production of the receptor or a rapid degradation, possibly as a result of phosphorylation of the receptor in an early biosynthetic cellular compartment. Control of newly synthesized IL-4Ralpha-chain protein expression by phosphatase may provide a novel means to regulate IL-4 responsiveness.     

Protein synthesis in imbibing wheat embryos.

Polypeptides synthesized by imbibing wheat embryos have been compared with those made by cell-free extracts programmed with bulk poly(A)-rich RNA from dry wheat embryos. Newly synthesized polypeptides, labeled with [35S]methionine, were resolved by one-dimensional and two-dimensional electrophoresis and then records of the separations were prepared by fluorography. When programmed by bulk poly(A)-rich RNA from dry wheat embryos, a nuclease-treated rabbit reticulocyte lysate synthesizes an array of polypeptides which is broadly similar to that formed when a wheat germ extract is programmed with the same RNA. Polypeptides made in both homologous and heterologous cell-free systems, under the direction of bulk poly(A)-rich RNA from dry wheat embryos, are broadly similar to those formed during early (0--40 min) imbibition of dry wheat embryos. As imbibition progresses beyond 40 min, there are profound changes in the one-dimensional and two-dimensional electrophoretic distributions of newly made polypeptides present in the 23 000 x g supernatant fraction of cell-free homogenates; characteristically, low-molecular-weight and basic polypeptides comprise a diminishing proportion of the total polypeptides as imbibition progresses beyond 40 min. Ribosomal proteins are conspicuous among the proteins formed during early imbibition and especially prominent among the products formed when homologous cell-free polypeptide synthesis is programmed by bulk poly(A)-rich RNA from dry wheat embryos.     

Protein tyrosine phosphatase activity inLeishmania donovani

L. Donovani promastigotes were grown to late-log and 3-day stationary phase to determine the level of protein tyrosine phosphatase activity in crude extracts and in fractions following gel filtration column chromatography. Over 90% of the activity was soluble in a low salt extraction buffer in both phases of growth. Several peaks of activity were resolved following gel filtration of the crude extracts indicating that multiple tyrosine phosphatases are present in these cells. Tyrosine phosphatase activity was lower in 3-day stationary than in late log-phase cells and a reduction in the major peak of activity, eluting in a gel fraction corresponding to an M _r of approximately 168kDa, was observed.In vivo tyrosine phosphorylation was revealed by Western blot analysis. The degree of phosphorylation of at least two proteins differed in cells obtained from late log phase cultures as compared with 3-day stationary phase cultures. These observations indicate that changes in the balance between tyrosine phosphorylation and dephosphorylation occur with increasing culture age.Abbreviations MBP myelin basic protein - PMSF phenyl-methanesulfonylfluoride - PTP protein tyrosine phosphatase - RCML reduced, carboxyamidomethylated, maleylated lysozyme - YINAS Tyr-Ile-Asn-Ala-Ser     

Sucrose and fructan metabolism in wheat roots at chilling temperatures

Sucrose and fructan metabolism were studied in wheat ( Triticuin aotiirum L. cv. Tribal 800) roots during a period at chilling temperature. Enzyme activities related to fructan and sucrose metabolism were measured. Sucrose-sucrose fructosyl transfer-ase (EC 2.4.1.99) activity increased more than 25-fold when plants were cooled to 4°C. Sucrose synthase (EC 2.4.1.13) and sucrose-phosphate synthase (EC 2.4.1.14) activities also increased, but low temperatures had no significant effect on invertaso (EC 3.2.1.26) or on fructan hydrolase (EC 3.2.1.26) activities. The accumulation pattern of fructan in roots was different to that in leaves. In roots chilling stimulated the synthesis of fructans of high degree of polymerization.     

Protein phosphatase activity in acetylcholine receptor-enriched membranes.

Phosphorylation of the acetylcholine receptor (AChR)¹ has been demonstrated in AChR-enriched membranes prepared from the electric organ of $\text{Torpedo californica}$. In this report we show that the same AChR-enriched membrane fraction also contains phosphoprotein phosphatase activity which dephosphorylates both the endogenous AChR and exogenous phosphorylated casein. Release of [³²P] PO₄ from phosphorylated casein was shown to be inhibited by F^? as well as GTP. cAMP and cGMP were without effect. Dephosphorylation of the membrane-bound AChR was also inhibited by F^?. This phosphorylation-dephosphorylation mechanism may play a role in mediating the function of the AChR at the synapse.     

Protein phosphatase activity is necessary for myofibrillogenesis

During myofibrillogenesis, myosin light-chain kinase (MLCK) phosphorylates the regulatory light chain (RLC) of myosin II, enabling patterned assembly of myosin thick filaments. A protein phosphatase (PP) has been shown to mediate RLC dephosphorylation in adult smooth and striated muscle. A role for PP activity in regulating myofibrillogenesis during embryonic development, however, has not been investigated. Tautomycin (TM) was used to inhibit both PP1 and PP2A activities, whereas okadaic acid (OA) and fostriecin (FOS) were used to inhibit PP2A. TM affected both actin and myosin assembly at 5nM; the IC50 value was 20 and 8.5nM, respectively. In contrast, OA applied at 10 times above its reported Ki for PP2A caused no significant disruption. There was also no disruption when FOS was applied at a concentration 30 times above its reported Ki for PP2A. Thus, our results suggest a primary role for PP1 isoforms during myofibrillogenesis. Although rho kinase (RK) regulates PP activity in embryonic smooth and cardiac muscle, application of the RK inhibitor Y27632 did not affect actin or myosin assembly in skeletal myocytes. Collectively, our pharmacological results suggest that PP1 is involved in dynamic regulation of RLC phosphorylation. To specifically test involvement of the myosin-targeted isoform (PP1M), we used a morpholino antisense approach to knock down the myosin targeting (M) subunit of PP1. Embryos injected with morpholino targeted to the 110-kDa M targeting subunit had fewer somites, and myosin organization was significantly perturbed. The combined pharmacological and molecular results suggest a dynamic equilibrium between MLCK and PP1M activities is required for proper myofibrillogenesis.     

Platelet-activating factor induction of secreted phosphatase activity in Trypanosoma cruzi

The effects of platelet-activating factor (PAF) on the ecto-phosphatase activity of Trypanosoma cruzi were investigated. Living parasites hydrolyzed p-nitrophenyl phosphate (p-NPP) at a rate of 5.71 +/- 0.37 nmol P(i) mg(-1) min(-1). This ecto-phosphatase activity increased to 8.70 +/- 1.12 nmol P(i) mg(-1) min(-1) when the cells were grown in the presence of 10(-9) M PAF. This effect was probably due to stimulation of the release of the ecto-phosphatase and/or the secretion of an intracellular phosphatase to the extracellular medium, as suggested by cytochemical analysis. Modulation of the ecto-phosphatase activity was also observed when PAF was added during the time course of the reaction. WEB 2086, a competitive PAF antagonist, was able to revert PAF effects when both were used at the same concentration. When PAF was added to a membrane enriched fraction preparation of T. cruzi, no alteration on the phosphatase activity was observed. This result suggests an involvement of intracellular signaling, as PAF was only effective on intact cells. Sphingosine and phorbol-12-myristate-13-acetate (PMA) were then used to investigate a possible involvement of protein kinase C (PKC) with PAF-induced phosphatase secretion. Sphingosine by itself stimulated the secretion of a phosphatase but did not significantly interfere with PAF effects on this enzyme. On the other hand, PMA was able to abrogate PAF-induced release of this phosphatase. These data are highly suggestive of a putative involvement of signal transduction mediated by a ligand of mammalian origin (PAF), through PKC and a specific receptor located on the cell surface of the human parasite Trypanosoma cruzi.     

Rapid induction of alkaline phosphatase activity by retinoic acid

Retinoic acid (vitamin A acid) increased alkaline phosphatase activity in cultured cells derived from both normal rat prostate and the Dunning R-3327 transplantable prostatic adenocarcinoma. Retinoic acid was found to be 3–4-fold more effective as an inducer of enzyme activity than retinol or retinal. In one rapidly-growing cell line (UMS-1541Q) which has a barely-detectable level of enzyme activity in the uninduced state, increased activity could be detected as early as 3–4 hours after the addition of 10μM retinoic acid. This increase was totally blocked by actinomycin D and cycloheximide. The demonstrated rapid inducibility of alkaline phosphatase activity provides a specific marker for the action of retinoic acid at the molecular level.     

水氮互作对小麦土壤水分利用和茎中果聚糖含量的影响

通过田间试验,以强筋小麦济麦20为材料,设置3个施氮水平：0 kg·hm^-2（N₀）、180 kg·hm^-2（N₁）、240 kg·hm^-2（N₂）;4个灌水处理：不灌水（W₀）、底墒水+拔节水+开花水（W₁）、底墒水+冬水+拔节水+开花水(W₂)、底墒水+冬水+拔节水+开花水+灌浆水(W₃),每次灌水量为60 mm,研究水氮互作对土壤水分含量、旗叶光合速率、倒二茎中果聚糖含量及氮肥和水分利用效率的影响.结果表明：施氮水平为180 kg·hm^-2处理的旗叶光合速率和倒二茎中果聚糖含量较高,籽粒产量、氮肥表观利用效率、氮肥农学利用率和水分利用效率最高;施氮水平为240 kg·hm^-2处理的茎中果聚糖含量较高;不施氮（N₀）或施氮过多（N₂）均不利于小麦籽粒产量、氮肥和水分利用效率的提高.W₁水分处理促进了倒二茎中果聚糖的积累和向籽粒的转运,有利于产量的提高.180 kg·hm^-2施氮水平配合灌溉底墒水+拔节水+开花水的水氮交互处理（N₁W₁）具有较高的籽粒产量及较高的氮肥和水分利用效率,在此基础上增加施氮量或灌水量,小麦旗叶光合速率和倒二茎中果聚糖含量升高,籽粒产量无显著变化或降低,氮肥和水分利用效率降低.     

The activity of catalase and phosphatase in wheat when controlling the growth rate

K-humát stimuloval r?st p?enice a byla zji?těna zvý?ená aktivita fosfatázy v listech i v ko?enech a zvý?ená aktivita katalázy pouze v ko?enech. Vy??í teplota (30° C) p?i kultivaci zp?sobila pokles aktivity fosfatázy v ko?enech i v listech a pokles aktivity katalázy v listech. Narkotizace klí?ních rostlinek chloroformem zpomaluje r?st, zvy?uje aktivitu fosfatázy jen v prvních dnech po zásahu a zvy?uje aktivitu katalázy. Rovně? odnětí endospermu mělo za následek zpomalený r?st. P?enice takto vypěstovaná měla zvý?enou aktivitu katalázy a fosfatázy. Aktivita fosfatázy v listech v?ech variant i kontrol byla podstatně ni??í ne? v ko?enech na rozdíl od katalázy, která byla v listech a? několikanásobně aktivněj?í ne? v ko?enech. Aktivita fosfatázy v listech i v ko?enech klesala ve vét?ině p?ípad? se stá?ím. Aktivita katalázy klesala se stá?ím pouze v ko?enech, zatím co v listech stoupala. Aktivita katalázy je pravděpodobně méně závislá na rychlosti r?stu a souvisí spí?e s vý?ivou, tvorbou chlorofylu, fotosyntetickou aktivitou apod. Jak z literárních údaj?, tak z na?ich výsledk? vyplývá, ?e neexístuje jednoduchý vztah mezi aktivitou sledovaných enzym? a rychlostí r?stu; jde o vztahy komplikovaněj?í.     

Sucrose and fructan metabolism of different wheat cultivars at chilling temperatures

Four wheat ( Triticum aestivum L.) varieties cultivated in different climates from subtropics to North Patagonia were used to study sucrose and fructan metabolism in plants when submitted to a cold period. Higher levels of sugars were found in the more cold tolerant cultivars. Sucrose synthase (EC 2.4.1.13) and sucrose phosphate synthase (EC 2.4.1.14) activities showed a 2–3 fold increase when plants were grown at 4°C for 10 days. The more cold-tolerant wheat cultivars also showed the higher levels of enzyme activities. These metabolical changes were not due to anatomical or morphological differences produced during growth at 4°C