Research for the mechanisms of Mn uptake in lettuce and role of Mn in low pH induced root hair-formation

低pH条件下生菜主根的生长受到抑制，低pH条件下生长的几乎所有根表皮细胞都诱导出根毛，以补偿根系吸收水分的能力。在低pH下，Mn的吸收量减少到1/5。中性pH培养基中Mn的消除与低pH培养基一样，诱导根毛的形成，而在低pH培养基中添加过量的Mn则抑制根毛的形成。本研究更精确地确定了Mn在低pH诱导的根毛形成中的作用。用放射性的^<54>Mn测定Mn的吸收速率和位置。在降低培养基pH后1小时内，Mn的吸收速率降低到1/3左右。中性pH培养基中去除Mn诱导的根毛形成的时间过程和位置与低pH诱导的相似。这些结果表明，低pH诱导的Mn吸收能力降低是生菜幼苗产生根毛的原因（Konno， M. et al. 2006）。为了明确莴苣中的Mn转运体，我们构建了一个缺乏两个Mn转运体的酵母突变株。将假定的莴苣Mn转运基因Ls-MDR1转化到酵母突变体中不能挽救突变体对Mn的需求。用所谓的“霰弹枪法”将生菜基因转化为突变体，发现了一个候选Mn转运基因。在中性pH条件下，施用氢离子泵抑制剂钒酸盐可诱导根毛形成。这表明低pH可能首先影响氢离子泵送能力，然后由于氢离子泵送能力的降低而降低了对锰的吸收。

Growth of lettuce main roots are suppressed in low pH. Root hairs are induced on the almost all root epidermal cells grown in low pH to compensate the ability of root water uptake. In low pH, Mn uptake is reduced to 1/5. Elimination of Mn from neutral pH media induced root hair-formation like as low pH. On the other hand, addition of excess Mn in low pH media suppresses root hair formation. We determined role of Mn in low pH induced root hair-formation more precisely in this research.Rate and position of Mn uptake were determined using radioactive ^<54>Mn. Rate of Mn uptake was reduced to about 1/3 within 1 hr after lowering of medium pH. Time-course and position of root hair-formation which was induced by elimination of Mn from neutral pH medium were similar to those were induced by low pH. These results indicated that low pH induced reduction of Mn uptake ability was the cause of root hair initiation in lettuce seedlings (Konno, M. et al. 2006).To make clear Mn transporter(s) in lettuce, we constructed an yeast mutant strain which lacked two Mn transporter. Transformation of putative lettuce Mn transporter gene(Ls-MDR1) to the yeast mutant could not rescue Mn requirement of the mutant. Transformation of lettuce genes to the mutant by so called shot-gun method showed one candidate of Mn transporter gene.Application of H^+ pump inhibitor vanadate could induce root hair formation in neutral pH. This results indicated the possibility that low pH at first affected on the H+ pump ability then Mn uptake was reduced by the decrease of H+ pump ability.