Potassium Uptake and Transport in Apple Roots Under Drought Stress

Abstract

As one of the most important mineral nutrient elements, potassium (K+) plays an important role in many plant physiological processes and determines both the yield and quality of crops. There are two typical gene families that regulate K+ transport in higher plants, including K+ channels and K+ transporters. However, little is known about how these channels and transporters divide their work in response to drought stress. In this study, the hydroponic experiment was conducted on Malus hupehensis. The K+ content was found to decrease in response to drought stress in M. hupehensis, the aboveground decreased by 34.15% and the underground decreased by 3.97%. Meanwhile, the root morphology change was detected by scanning the root system. Under conditions of drought, the genes encoding K+ transporters were upregulated including MdCHX1.3, MdCHX4.11, MdCHX4.8, MdCHX4.9, MdHKT1, and MdHAK3.2. The net influx of K+ was inhibited by 19.47% with the action of K+ channel inhibitors (CsCl), however a significant decrease (80.99%; P < 0.05) was found in roots exposed to a PM H+-ATPase (orthovanadate) inhibitor by utilizing a non-invasive micro-test technique. The trend of H+ efflux was similar to that of K+. The data suggested that the positive influx of K+ through the transporter accounted for the main K+ uptake under drought stress. These results suggest that we can improve the uptake of K+ by purposely up-regulating specific K+ transporters under drought stress. This process may improve growth, yield, quality, and stress tolerance in apple trees.