Potassium is an essential macronutrient that has been partly overshadowed in root science by nitrogen and phosphorus. The current boom in potassium-related studies coincides with an emerging awareness of its importance in plant growth, metabolic functions, stress tolerance, and efficient agriculture. In this review, we summarized recent progress in understanding the role of K⁺ in root growth, development of root system architecture, cellular functions, and specific plant responses to K⁺ shortage. K⁺ transport is crucial for its physiological role. A wide range of K⁺ transport proteins has developed during evolution and acquired specific functions in plants. There is evidence linking K⁺ transport with cell expansion, membrane trafficking, auxin homeostasis, cell signaling, and phloem transport. This places K⁺ among important general regulatory factors of root growth. K⁺ is a rather mobile element in soil, so the absence of systemic and localized root growth response has been accepted. However, recent research confirms both systemic and localized growth response in Arabidopsis thaliana and highlights K⁺ uptake as a crucial mechanism for plant stress response. K⁺-related regulatory mechanisms, K⁺ transporters, K⁺ acquisition efficiency, and phenotyping for selection of K⁺ efficient plants/cultivars are highlighted in this review.

Radiocaesium is a pollutant with a high risk for the environment, agricultural production, and human health. It is mobile in ecosystems and can be taken up by plants via potassium transporters. In this study, we focused on the role of potassium transporter AtKUP7 of the KT/HAK/KUP family in Cs⁺ and K⁺ uptake by plants and in plant tolerance to caesium toxicity. We detected that Arabidopsiskup7 mutant accumulates significantly lower amounts of ¹³⁴Cs in the root (86%) and in the shoot (69%) compared to the wild-type. On the other hand ability of the mutant to grow on media with toxic (100 and 200 µM) concentrations of Cs⁺ was not changed; moreover its growth was not impaired on low K⁺. We further investigated another mutant line in AtKUP7 and found that the growth phenotype of the kup7 mutants in K⁺ deficient conditions is much milder than previously published. Also, their accumulation of K⁺ in shoots is hindered only by severe potassium shortage.