Department of Chemistry & Biochemistry, University of Missouri-St. Louis, MO 63121, United States.
J Agric Food Chem. 2012 Jun 20;60(24):6077-87. doi: 10.1021/jf3004288. Epub 2012 Jun 11.
Essential nutrients such as trace metal ions, amino acids, and sugars are transported in the phloem from leaves to other parts of the plant. The major chelating agents in phloem include nicotianamine, histidine, cysteine, glutamic acid, and citrate. A computer model for the speciation of metal ions in phloem has been used to assess the degree to which the widely used herbicide glyphosate binds to Fe(3+), Fe(2+), Cu(2+), Zn(2+), Mn(2+), Ca(2+), and Mg(2+) in this fluid over the pH range of 8 to 6.5. The calculations show that glyphosate is largely unable to compete effectively with the biological chelating agents in phloem. At a typical phloem pH of 8, 1.5 mM glyphosate binds 8.4% of the total Fe(3+), 3.4% of the total Mn(2+), and 2.3% of the total Mg(2+) but has almost no effect on the speciation of Ca(2+), Cu(2+), Zn(2+), and Fe(2+). As the pH decreases to 6.5, there are some major shifts of the metal ions among the biological chelators, but only modest increases in glyphosate binding to 6% for Fe(2+) and 2% for Zn(2+). The calculations also indicate that over 90% of the glyphosate in phloem is not bound to any metal ion and that none of the metal-glyphosate complexes exceed their solubility limits.
必需营养物质，如痕量金属离子、氨基酸和糖，通过韧皮部从叶片运输到植物的其他部位。韧皮部中的主要螯合剂包括烟碱酸、组氨酸、半胱氨酸、谷氨酸和柠檬酸。已经使用一种用于韧皮部中金属离子形态的计算机模型来评估广泛使用的除草剂草甘膦与 Fe(3+)、Fe(2+)、Cu(2+)、Zn(2+)、Mn(2+)、Ca(2+)和 Mg(2+)在该液体中的结合程度，该液体的 pH 值范围为 8 到 6.5。计算表明，草甘膦在很大程度上不能有效地与韧皮部中的生物螯合剂竞争。在典型的韧皮部 pH 值为 8 时，1.5 mM 的草甘膦结合了总 Fe(3+)的 8.4%、总 Mn(2+)的 3.4%和总 Mg(2+)的 2.3%，但对 Ca(2+)、Cu(2+)、Zn(2+)和 Fe(2+)的形态几乎没有影响。当 pH 值降低到 6.5 时，生物螯合剂中的金属离子发生了一些主要的转移，但草甘膦与 Fe(2+)的结合率仅略有增加，为 6%，与 Zn(2+)的结合率仅略有增加，为 2%。计算还表明，韧皮部中超过 90%的草甘膦没有与任何金属离子结合，并且没有任何金属-草甘膦复合物超过其溶解度极限。
