Plants are able to grow under various nutritional environments by adapting to the conditions in which they live. If nutrients are scarce, plants regulate their metabolism through various signaling pathways in order to survive. Nutrient sensing and signaling are EX 527 active throughout a plant’s life span and are important for optimal plant growth. When nutrients are limiting, plants grow at a slower rate, change their nutrient utilization and acquisition, and adjust their metabolism and morphology in order to more effectively acquire the nutrients. In an agricultural system, a balanced supply of soil macronutrients, especially nitrogen, phosphorus, and potassium, is necessary to produce the optimum quantity and quality of crops. Within the plant, K is the most abundant inorganic cation, consisting of up to 1/10 of a plant’s dry weight. Potassium plays various roles in the plant, such as the activation of enzymes, stabilization of protein synthesis, neutralization of negative charges on proteins, maintenance of cytoplasmic pH homeostasis and osmotic balance, and the movement of other ions. Potassium deprivation rapidly induces the expression of two K transporters, HAK5, a high-affinity K uptake transporter and KEA5 in 6-week-old roots, whose expression is regulated by reactive oxygen species. However, while HAK5 expression is induced at any developmental stages of roots, KEA5 expression is not, making HAK5 a preferable marker gene in studies of low K responses. The relationship between the acquisition of different nutrients by mineral nutrient transporters and the imbalances triggered by a mineral deficiency are well documented. For instance, nitrate transporters are down-regulated when a plant is deprived of K ; several nutrient transporters are up-regulated by K and phosphorus deprivation in tomato roots ; and when plants experience K, nitrogen, phosphorus, and sulfur deprivation, they produce ROS in roots. Furthermore, the correlation between phytohormone signaling and nutrient signaling is well known. The K transporter TRH1 is required for root hair development and root gravitropism and functions in the auxin transporter system in Arabidopsis roots. The genes involved in auxin biosynthesis were down-regulated by K re-supply in K-starved roots. In addition, an Arabidopsis transcription factor, MYB77, has been shown to modulate the low K-dependent reduction of the lateral root density through auxin signal transduction. Ethylene is involved in the low K signaling pathway by inducing the production of ROS in roots and then changing root hair and primary root growth and up-regulating HAK5 expression in Arabidopsis. Moreover, many genes respond to K starvation, which leads to increased pathogen susceptibility; a process that is linked to jasmonic acid. The cytokinins regulate various processes within plants, including cell division and root and shoot morphogenesis. In Arabidopsis, the key CK biosynthetic enzymes are adenosine phosphate-isopentenyltransferases. It is fairly well known that interactions between nutrients and CKs influence nutrient signaling and adaptive responses in plants. Nitrate treatment induces the biosynthesis of CKs by up-regulating IPT3 and also triggers the expression of type-A ARRs in Arabidopsis. CKs are also linked systemically to phosphate deprivation signaling by repressing the expression of genes that are induced by phosphate starvation conditions.