Regulatory Roles of Cytokinins and Cytokinin Signaling in Response to Potassium Deficiency in Arabidopsis

Abstract

Potassium (K) is an important plant macronutrient that has various functions throughout the whole plant over its entire life span. Cytokinins (CKs) are known to regulate macronutrient homeostasis by controlling the expression of nitrate, phosphate and sulfate transporters. Although several studies have described how CKs signal deficiencies for some macronutrients, the roles of CKs in K signaling are poorly understood. CK content has been shown to decrease under K-starved conditions. Specifically, a CK-deficient mutant was more tolerant to low K than wild-type; however, a plant with an overaccumulation of CKs was more sensitive to low K. These results suggest that K deprivation alters CK metabolism, leading to a decrease in CK content. To investigate this phenomenon further, several Arabidopsis lines, including a CK-deficient mutant and CK receptor mutants, were analyzed in low K conditions using molecular, genetic and biochemical approaches. ROS accumulation and root hair growth in low K were also influenced by CKs. CK receptor mutants lost the responsiveness to K-deficient signaling, including ROS accumulation and root hair growth, but the CK-deficient mutant accumulated more ROS and exhibited up-regulated expression of HAK5, which is a high-affinity K uptake transporter gene that is rapidly induced by low K stress in ROS- and ethylene-dependent manner in response to low K. From these results, we conclude that a reduction in CK levels subsequently allows fast and effective stimulation of low K-induced ROS accumulation, root hair growth and HAK5 expression, leading to plant adaptation to low K conditions.

Interaction of cytokinins with UV-B (280 -315nm) on the expansion growth of cucumber cotyledons

“…[25][26][27] Exogenous application of cytokinins has been reported to increase the stress-tolerance capacity of plants indicating a beneficial effect of CKs in the regulation of plants adaptation to environmental stresses. Thus several studies with abiotic stresses like heavy metals, drought, salt and high temperature have reported that CKs could be involved in regulating antioxidant defence, while information on regulation of antioxidant metabolism under UV-B stress by CKs is lacking.…”

The Arabidopsis nitrate transporter NPF7.3/NRT1.5 is involved in lateral root development under potassium deprivation

“…15 The K C nutritional status is linked to the ethylene, cytokinin, jasmonic acid and auxin signaling pathways, thus leading to developmental and physiological alterations. [16][17][18] Moreover, it presumably influences plant disease resistance. 19 When grown under limiting K C supply, total root size was reduced in 26 investigated natural Arabidopsis accessions, but the degree of reduction and the root architectural response to K C limitation strongly differed between accessions.…”

NPKS uptake, sensing, and signaling and miRNAs in plant nutrient stress

“…Phytohormones needed for the plant growth and development and also play an important role in nutrient response . In response to nutrient stress, different phytohormones involve in nutrient homeostasis, e.g., auxin, cytokinin (CK) (N, P, K, and S stress), abscisic acid (ABA), gibberellic acid (GA) (P stress) (MaruyamaNakashita et al 2004;Franco-Zorrilla et al 2005;Rubio et al 2009;Ruffel et al 2011;Nam et al 2012;Rigas et al 2013;Shen et al 2013). Auxin, CK, and ABA intimately linked with N signaling and involved in regulating N acquisition, RSA modification in response to N stress (Kiba et al 2011).…”