Screening of As-accumulating plants using a foliar application and a native accumulation of As

The discovery of novel accumulating plants is useful for efficient phytoremediation due to the demands of various conditions of impacted sites such as land use, soil properties, concentration of pollutants, and climate. In the present study, we investigated foliar application or a field with highly bioavailable arsenic (As) to screen As-accumulating plants. Plants grown in the downstream of a hot springs area were analyzed for native As accumulation and As foliar application, and the rhizosphere soils were collected. The water-soluble As in the rhizosphere soils had a high average, 144 microg/kg, whereas total As was similar to normal soil in Japan. Among 34 herbaceous plants and 17 woody plants, Chelidonium majus var. asiaticum accumulated a relatively high As level, 8.07 mg/kg DW (93.6% of As added), that was not revealed by native accumulation. In a further pot experiment, C. majus accumulated a moderately high As level (314 mg/kg DW) in the roots but not in the shoot (30.1 mg/kg DW), and exhibited a low transfer factor (TF = 0.096). Thus, a foliar application would be a simple and high-throughput method to screen plants that accumulate and tolerate As. C. majus would be useful as a tool for phytostabilization of As.

Apoptosis in skin pigment cells of the medaka, Oryzias latipes (Teleostei), during long-term chromatic adaptation: the role of sympathetic innervation

Many teleost fish can adapt their body color to a background color by changing the morphology and density of their skin pigment cells. Melanophore density in fish skin decreases during long-term adaptation to a white background. Although cell death, especially apoptosis, is thought to be involved in these morphological changes, there are no data clearly supporting this mechanism. Using medaka fish, Oryzias latipes, we observed that, on a white background, melanophore size was reduced first and this was followed by a decrease in melanophore density caused by gradual cell death. The process of cell death included loss of cell activity, cell fragmentation, phagocytosis of the fragments, and clearance via the epidermis. Apoptosis was assessed by the appearance of phosphatidylserine on the cell surface of melanophores that had lost motile activity, and DNA fragments involved in cell fragmentation were detected by the TUNEL (TDT-mediated dUTP-biotin nick end-labeling) assay. However, when chemically denervated fish were used, although melanophore size was reduced as expected, cell death was suppressed even on a white background. In skin tissue culture, apoptosis in melanophores was stimulated significantly by norepinephrine, but not by melanin-concentrating hormone. These results indicate that melanophore density decreases by apoptosis, and suggest that sympathetic innervation has an important role in the regulation of apoptosis in melanophores. In analogous fashion, leucophores showed a significant decrease in density with an increase of cell death on a black background. We suggest that apoptosis regulates the balance of pigment cells in the skin of medaka fish to adapt their body color to a particular background.

Acyloxycoumarinylmethyl-caged cAMP, the photolabile and membrane-permeable derivative of cAMP that effectively stimulates pigment-dispersion response of melanophores

Two acyloxycoumarinylmethyl-caged cAMPs (ACM- and PCM-cAMP) have been synthesized using a silver (I) oxide promoted method. Introduction of the acyloxy group to the 7-position on the coumarin ring not only enhanced the membrane permeability but diminished the photolability of the coumarin-cage. Because intracellular enzymatic hydrolysis of the 7-acyloxy group would produce the 7-hydroxy moiety which is more hydrophilic and photolabile, application of acyloxycoumarinylmethyl-caged cAMPs in biological studies would be expected to be efficient. Thus, the effect of extracellularly applied ACM- and PCM-cAMP had been investigated using the motile response of fish melanophores. After irradiation, a significant enhancement in the motility responses was observed. The observed magnitudes of the dispersions are comparable to that of Bt2cAMP/AM which is known as a membrane permeable cAMP derivative.