Université de Lorraine, Laboratoire Sols et Environnement UMR 1120 (ENSAIA)INPL-INRA, BP 172, 54505 Vandoeuvre-les-Nancy Cedex, France.
J Exp Bot. 2012 Oct;63(16):5815-27. doi: 10.1093/jxb/ers230. Epub 2012 Sep 17.
Solute active transport or exclusion by plants can be identified by the values of the Transpiration Stream Concentration Factor (TSCF=xylem:solution solute concentration ratio). The aim of this study was to estimate this parameter for Ni uptake by the Ni-hyperaccumulator Leptoplax emarginata or the Ni-excluder Triticum aestivum cultivar 'Fidel'. The Intact Plant TSCF for nickel (IPTSCF(Ni)) was calculated as the ratio between the nickel mass accumulation in the leaves and the nickel concentration in solution per volume of water transpired. Predominantly, Ni active transport occurred for L. emarginata, with IPTSCF(Ni) values of 4.7-7.2 and convective component proportions of the root Ni uptake flow of only 15-20% for a range of Ni concentrations in solutions of 2-16 µmol Ni l(-1), regardless of the growth period and the time of Ni uptake. Hyperaccumulator roots were permeable to both water and nickel (mean reflection coefficient for Ni, σ(Ni), of 0.06), which was mainly attributed to an absence of exodermis. Results provide a new view of the mechanisms of Ni hyperaccumulation. By contrast, the wheat excluder was characterized by an extremely low mean IPTSCF(Ni) value of 0.006, characterizing a predominantly Ni sequestration in roots. From a methodological viewpoint, the 'microscopic' TSCF(Ni), measured directly on excised plants was 2.4 times larger than its recommended 'macroscopic' IPTSCF(Ni) counterpart. Overall, IPTSCF and σ determined on intact transpiring plants appeared to be very useful biophysical parameters in the study of the mechanisms involved in metal uptake and accumulation by plants, and in their modelling.
植物的溶质主动运输或排斥可以通过蒸腾流浓度因子（TSCF=xylem：溶液溶质浓度比）的值来识别。本研究的目的是估算镍超积累植物 Leptoplax emarginata 或镍排斥小麦品种 'Fidel' 对镍的吸收的这个参数。完整植物 TSCF 对镍（IPTSCF（Ni））的计算方法是叶片中镍质量积累与每蒸腾水量的镍浓度之比。主要情况下，镍发生主动运输，L. emarginata 的 IPTSCF（Ni）值为 4.7-7.2，根镍吸收流的对流分量比例仅为 15-20%，在 2-16 μmol Ni l(-1)的一系列镍浓度下，无论生长时期和镍吸收时间如何。超积累植物的根对水和镍都是可渗透的（镍的平均反射系数，σ（Ni）为 0.06），这主要归因于没有外表皮。结果提供了对镍超积累机制的新认识。相比之下，小麦排斥者的特征是非常低的平均 IPTSCF（Ni）值为 0.006，表明主要在根部镍被隔离。从方法学的角度来看，直接在离体植物上测量的“微观”TSCF（Ni）比其推荐的“宏观”IPTSCF（Ni）大 2.4 倍。总的来说，在蒸腾植物上测定的 IPTSCF 和 σ 似乎是研究植物金属吸收和积累机制及其建模的非常有用的生物物理参数。
