硫化カドミウムの高濃度添加時における小麦の生育とカドミウム集積濃度に対する炭酸カルシウムの影響

In Japan, wheat is usually cultivated from December to June as a second crop in the same field as rice. In Cd-polluted areas, the fields are affected by both wastewater and the emissions from the chimneys of zinc refineries or plating factories. The application of inhibition agents, such as slaked lime, calcium silicate or fused magnesium are applied to inhibit the absorption of these metals by plants. Many reports have been made on the decrease of metal absorption through the application of some form of calcium, phosphate or silicate. Also, it has been reported that wheat is more sensitive to CdS than to CdO. However, almost all experiments were performed at less than 500 ppm Cd in soil, and these experiments have not been made at a concentration close to the level critical for wheat plants. There have been few reports on the effects of calcium cabonate on metal tolerance or metal uptake at the a level critical wheat. The typical example of using calcium carbonate was investigated by Maeda, and the application of phosphate by Koshino, and by Muramoto et al. The effects of calcium carbonate on the metal content of wheat to the critical levels were examined.植物に対する有害金属の生育限界濃度域での実験は極めて少ない。ここでは、小麦の硫化カドミウム（CdS）に対する生育限界濃度と小麦穀粒中カドミウム含有量に及ぼす炭酸カルシウム添加栽培の影響を調べた。その結果、硫化カドミウムに対する小麦の生育限界濃度は1,500ppmであり、その時の小麦穀粒中のカドミウム含有量は123.2μg/g（乾燥物中）であることが判明した。すなわち溶解度の低いカドミウムの化学形においても、穀粒中への集積が生じる結果が表示された。また、炭酸カルシウムの同時添加により、無添加に対して1,500ppm区では穀粒中のカドミウム含有量は57％減少し、小麦の生育限界濃度5,000ppmに拡大された。茎葉長、茎葉重、穀粒重等の各生育項目において炭酸カルシウムの添加効果が見られ、特にカドミウム濃度500-5,000ppmの間では炭酸カルシウム添加によるカドミウム毒性の抑制現象が有意に認められた。このことは高濃度カドミウム汚地域における炭酸カルシウムによる植物保護の一策としての有効性を示唆したと考えられる

PTP1B Inhibition Causes Rac1 Activation by Enhancing Receptor Tyrosine Kinase Signaling

Background/Aims: The present study investigated the signaling pathway underlying Rac1 activation induced by the linoleic acid derivative 8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA). Methods: Activity of protein tyrosine phosphatase 1B (PTP1B) was assayed under cell-free conditions. Western blot was carried out to quantify phosphorylation of insulin receptor substrate-1 (IRS-1) and Akt in PC-12 cells. Rac1 activity was monitored in the föerster resonance energy transfer (FRET) analysis using living and fixed PC-12 cells. Results: DCP-LA markedly suppressed PTP1B activity in a concentration (100 pM-100 µM)-dependent manner. In the DCP-LA binding assay, fluorescein-conjugated DCP-LA produced a single fluorescent signal band at 60 kDa, corresponding to the molecule of PTP1B, and the signal was attenuated or abolished by co-treatment or pretreatment with non-conjugated DCP-LA. DCP-LA significantly enhanced nerve growth factor (NGF)-stimulated phosphorylation of IRS-1 at Tyr1222 and Akt1/2 at Thr308/309 and Ser473/474 in PC-12 cells. In the FRET analysis, DCP-LA significantly enhanced NGF-stimulated Rac1 activation, which is abrogated by the phosphatidylinositol 3 kinase (PI3K) inhibitor wortmannin, the 3-phosphoinositide-dependent protein kinase-1 (PDK1) inhibitor BX912, or the Akt inhibitor MK2206. Conclusion: The results of the present study show that DCP-LA-induced PTP1B inhibition, possibly through its direct binding, causes Rac1 activation by enhancing a pathway along a receptor tyrosine kinase (RTK)/IRS-1/PI3K/Akt/Rac1 axis

Crosstalk between PI3 Kinase/PDK1/Akt/Rac1 and Ras/Raf/MEK/ERK Pathways Downstream PDGF Receptor

Background/Aims: Our earlier studies suggested crosstalk between IRS/PI3 kinase/PDK1/Akt/Rac1/ROCK and (Shc2/Grb2/SOS)/Ras/Raf/MEK/ERK pathways downstream PDGF-ββ receptor responsible for chemotaxis and proliferation of malignant mesothelioma cells. The present study was conducted to obtain evidence for this. Methods: To assess activation of Akt, MEK, and ERK, Western blotting was carried out on MSTO-211H malignant mesothelioma cells using antibodies against phospho-Thr308-Akt, phopho-Ser473-Akt, Akt, phospho-MEK, MEK, phopho-ERK1/2, and ERK1/2. To knock-down Akt, PI3 kinase, PDK1, and Rac1, siRNAs silencing each-targeted gene were constructed and transfected into cells. To monitor Rac1 activity, FRET monitoring was carried out on living and fixed cells. Results: ERK was activated under the basal conditions in MSTO-211H cells, and the activation was prevented by inhibitors for PI3 kinase, PDK1, Akt, and Rac1 or by knocking-down PI3 kinase, PDK1, Akt, and Rac1. Akt was also activated under the basal conditions, and the activation was suppressed by a MEK inhibitor and an ERK1/2 inhibitor. In the FRET analysis, Rac1 was activated under the basal conditions, and the activation was inhibited by a MEK inhibitor and an ERK1/2 inhibitor. Conclusion: The results of the present study show that ERK could be activated by PI3 kinase, PDK1, Akt, and Rac1 and that alternatively, Akt and Rac1 could be activated by MEK and ERK in MSTO-211H cells