Optimization of potassium for proper growth and physiological response of Houttuynia cordata Thunb

Houttuynia cordata Thunb. is an edible herb with a variety of pharmacological activities, but only limited information is available about its response towards potassium supplementation. Sterile plantlets were cultured in media with different potassium levels, and parameters related to growth, foliar potassium, water and chlorophyll contents, photosynthesis, transpiration, H₂O₂ contents and antioxidative enzyme activities were determined after a month. Results showed that 1.28 mM potassium was the optimum for H. cordata as highest values of dry weight, shoot height, root length and number were obtained at this concentration. The optimum potassium concentration resulted in the maximum net photosynthetic rate which could be associated with the highest chlorophyll content rather than limited stomatal conductance. The supply of surplus potassium resulted in higher content of foliar potassium, but negatively correlated with the biomass. Both potassium starvation (0 mM) and high potassium (>1.28 mM) could lead to water loss through high transpiration rate and low water absorption, respectively, and resulted in H₂O₂ accumulation and increased activities of catalase and peroxidase, which suggested induction of oxidative stress. Moreover, H. cordata showed the minimum of H₂O₂ content and the maximum of superoxide dismutase activity on 1.28 mM potassium, implying its role in inducing tolerance against oxidative stress.