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

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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.