High-affinity K+ uptake in pepper plants

High-affinity K+ uptake is an essential process for plant nutrition under K+-limiting conditions. The results presented here demonstrate that pepper (Capsicum annuum) plants grown in the absence of \(NH₄^{{+}}\) and starved of K+ show an \(NH₄^{{+}}\) -sensitive high-affinity K+ uptake that allows plant roots to deplete external K+ to values below 1 μM. When plants are grown in the presence of \(NH₄^{{+}},\) high-affinity K+ uptake is not inhibited by \(NH₄^{{+}}\) ⁠. Although \(NH₄^{{+}}\) -grown plants deplete external K+ below 1 μM in the absence of \(NH₄^{{+}},\) when 1 mM \(NH₄^{{+}}\) is present they do not deplete external K+ below 10 μM. A K+ transporter of the HAK family, CaHAK1, is very likely mediating the \(NH₄^{{+}}\) -sensitive component of the high-affinity K+ uptake in pepper roots. CaHAK1 is strongly induced in the roots that show the \(NH₄^{{+}}\) -sensitive high-affinity K+ uptake and its induction is reduced in K+-starved plants grown in the presence of \(NH₄^{{+}}\) ⁠. The \(NH₄^{{+}}\) -insensitive K+ uptake may be mediated by an AKT1-like K+ channel.