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Potassium Uptake and Transport in Apple Roots Under Drought Stress

Qi, Jianguo, Sun, Simin, Yang, Lin, Li, Mingjun, Ma, Fengwang, Zou, Yangjun
Horticultural plant journal 2019 v.5 no.1 pp. 10-16
H-transporting ATP synthase, Malus hupehensis, apples, drought, gene expression regulation, genes, horticultural crops, hydroponics, potassium, potassium channels, protons, root systems, roots, stress tolerance, transporters, trees, water stress
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.