5.2 ǀ Potassium
The levels of potassium and other cationic nutrients such as Mg2+ also tend to be low in highly-weathered inland valley soils and deficiencies in rice are common. Potassium deficiency exacerbates Fe toxicity through impaired root oxidising power and Fe exclusion, decreased crown root growth and lateral root formation, and decreased Fe2+ storage in roots (Li, Yang & Luo, 2001; Suriyagoda, Tränkner & Dittert, 2020). It is involved in maintaining normal activity of peroxidase, which breaks down H2O2 formed in the Fenton reaction in response to excess Fe (Wu et al., 2017). As with P deficiency, impaired membrane permeability under K deficiency may cause leakage of organic substrates into the rhizosphere, and resulting increased reducing conditions and Fe2+ formation.
Relations between high Fe2+ and rice K+ transporters have been investigated.OsAKT1 is thought to be the most important root K+transporter in rice (Golldack, Quigley, Michalowski, Kamasani & Bohnert, 2003; Li et al., 2014). Genome Wide Association Studies (GWAS) have suggested OsAKT1 is associated with shoot Fe regulation (Matthus et al., 2015). In studies with mutants lacking OsAKT1, under Fe toxic conditions root K uptake decreased and root to shoot Fe translocation increased, resulting in increased leaf bronzing, increased ROS damage, reduced chlorophyl content and impaired photosynthesis (Wu et al., 2019). Adequate K uptake protects rice plants under Fe stress via the regulation of Fe translocation from the root to shoot.