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Abstract
Potassium (K+) deficiency severely threatens crop growth and productivity. Calcium (Ca2+) signaling and its sensors play a central role in the response to low-K+ stress. Calmodulin (CaM) is an important Ca2+ sensor. However, the mechanism by which Ca2+ signaling and CaM mediate the response of roots to low-K+ stress remains unclear. In this study, we found that the K+ concentration significantly decreased in both shoots and roots treated with Ca2+ channel blockers, a Ca2+ chelator, and CaM antagonists. Under low-K+ stress, reactive oxygen species (ROS) accumulated, and the activity of antioxidant enzymes, NAD kinase (NADK), and NADP phosphatase (NADPase) decreased. This indicates that antioxidant enzymes, NADK, and NADPase might be downstream target proteins in the Ca2+-CaM signaling pathway, which facilitates K+ uptake in plant roots by mediating ROS homeostasis under low-K+ stress. Moreover, the expression of NtCNGC3, NtCNGC10, K+ channel genes, and transporter genes was significantly downregulated in blocker-treated, chelator-treated, and antagonist-treated plant roots in the low K+ treatment, suggesting that the Ca2+-CaM signaling pathway may mediate K+ uptake by regulating the expression of these genes. Overall, this study shows that the Ca2+-CaM signaling pathway promotes K+ absorption by regulating ROS homeostasis and the expression of K+ uptake-related genes in plant roots under low-K+ stress.
Highlights
Potassium (K+) is one of the most important macronutrients in the cells of higher plants and is indispensable for plant growth and development (Leigh and Wyn Jones, 1984)
Calcium signaling has often been noted in response to low-K+ stress, and treatments with Ca2+ channel blockers and Ca2+ chelators are often used in studies of Ca2+ signaling
These results indicate that NtCNGC3 and NtCNGC10 were involved in K+ uptake by tobacco roots under low-K+ stress and were regulated by Ca2+ signaling
Summary
Potassium (K+) is one of the most important macronutrients in the cells of higher plants and is indispensable for plant growth and development (Leigh and Wyn Jones, 1984). K+ is a soluble ion that is involved in many physiological processes, including plasma membrane hyperpolarization, stomatal movement, and osmotic regulation (Wang et al, 2013); it plays an important role in the response to various abiotic stresses in plants (Hasanuzzaman et al, 2018). As K+ cannot be synthesized in plant cells, K+ is typically acquired from the soil by in plants via the roots. The expression of genes for some transporters, channels, and signaling cascades in plant roots involved in uptake, transport, and transduction and distribution can be induced by K+ deficiency. There is, a need to explore the mechanism of K+ absorption and its role in determining the distribution of K+ under low-K+ stress
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