Wu L, Enberg A W, Guo X
Department of Environmental Horticulture, University of California, Davis 95616, USA.
Ecotoxicol Environ Saf. 1997 Aug;37(3):251-8. doi: 10.1006/eesa.1997.1550.
The effects of elevated selenium (Se) and salinity concentrations in the root zone on Se and salt secretion and accumulation were studied for an inland (Kesterson) and a coastal (Bodega Bay) saltgrass in sand culture and under greenhouse conditions. The results of this study indicate that the secretory mechanism of the saltgrass exhibits high ion specificity. Plants of both ecotypes were more efficient at Cl- and Na+ secretion than at SO4(2-) and Se secretion, suggesting that the saltgrass secretion mechanism is adapted primarily to saline environments high in NaCl. The saltgrass plants of the Kesterson ecotype secreted more Se than the Bodega Bay plants when treated with Se alone. However, the Bodega Bay plants secreted more Se than the Kesterson plants when the plants were treated with Se+NaCl. These differences reflect a ecotypical difference in which the Kesterson plants are more adaptive to the seleniferous soil, and the Bodega Bay plants are more adaptive to a coastal saline soil high in NaCl. Sulfate availability inhibited both Se accumulation and Se secretion in the plants of both ecotypes by approximately 98%. Ion secretion molar ratios of Na:Cl were calculated and the results suggest that Na+ secretion is dependent on the availability of Cl-. Selenium was taken up by plants with little discrimination, and thus it may be regarded as a master of chemical mimicry sharing similar physical and chemical properties with sulfur (S). Selenium and salt accumulation indices and secretion efficiency indices were calculated and found that the accumulation indices were higher for Se than for S, suggesting that Se uptake may be more passive and less regulated by active transport than S. Secretion efficiency was much higher for Na+ and Cl- than for Se and SO4(2-), but the efficiency indices between ecotypes were comparable, suggesting that the secretion mechanism in this species is designed mainly for adaptation of high NaCl concentrations. About 85% of the secreted Se was found in selenate form. This finding suggests that the mechanism of Se translocation and Se secretion in the saltgrass resembles the movement of selenate in xylem found in nonhalophytic plants. Less than 15% of organic Se was detected in the secretions and only trace amount of selenite was detected. Overall, the Se secretion mechanism in saltgrass does not seem to contribute substantial Se speciation in the plant soil system.
在砂培和温室条件下，研究了根际硒（Se）和盐分浓度升高对内陆（凯斯特森）和沿海（博德加湾）盐草中硒和盐分分泌及积累的影响。本研究结果表明，盐草的分泌机制表现出高度的离子特异性。两种生态型的植物在Cl-和Na+分泌方面比在SO4(2-)和Se分泌方面更有效，这表明盐草的分泌机制主要适应于NaCl含量高的盐环境。单独用Se处理时，凯斯特森生态型的盐草植物比博德加湾的植物分泌更多的Se。然而，当植物用Se+NaCl处理时，博德加湾的植物比凯斯特森的植物分泌更多的Se。这些差异反映了一种生态型差异，即凯斯特森植物更适应含硒土壤，而博德加湾植物更适应NaCl含量高的沿海盐土。硫酸根的有效性使两种生态型植物中的Se积累和Se分泌均受到约98%的抑制。计算了Na:Cl的离子分泌摩尔比，结果表明Na+分泌取决于Cl-的有效性。植物对硒的吸收几乎没有选择性，因此它可被视为一种化学模拟物，与硫（S）具有相似的物理和化学性质。计算了硒和盐分积累指数以及分泌效率指数，发现Se的积累指数高于S，这表明与S相比，Se的吸收可能更被动，受主动运输的调节更少。Na+和Cl-的分泌效率远高于Se和SO4(2-)，但生态型之间的效率指数相当，这表明该物种的分泌机制主要是为适应高NaCl浓度而设计的。约85%的分泌Se以硒酸盐形式存在。这一发现表明，盐草中Se的转运和分泌机制类似于非盐生植物木质部中硒酸盐的移动。分泌物中检测到的有机Se不到15%，仅检测到痕量的亚硒酸盐。总体而言，盐草中的Se分泌机制似乎对植物-土壤系统中的Se形态形成贡献不大。
