Accordance with their function, CK 4EGI-1 levels were decreased in WT plants under K-deficient conditions (Figure 1), whereas ABA levels increased [30]. Taken together, we propose a model in which plants adapt to K deprivation by triggering an efficient regulation of various hormonal biosynthesis and signal cascades, including CKs and CK signaling (Figure 6) [7,12,13,30]. Specifically, for CKs and CK signaling, we suggest that during K deprivation, CK metabolism is altered, leading to a decrease in CKs. A reduction in CK levels subsequently allows fast and effective stimulation of low K-induced ROS accumulation, root hair Peptide M web growth and HAK5 expression, leading to plant adaptation to low K conditions.Figure 6. A schematic model for the roles of CKs in low K signal pathway. Low K conditions lead to reduced levels of endogenous CKs, which are negative regulators under these conditions. Lower CK levels result in ROS production, HAK5 expression, and then altered root growth. Previous studies showed that ethylene is a positive regulator in 
low K signaling that controls ROS production, HAK5 expression as well as root hair growth [13]. ABA [30] and auxin [12] also are involved in controlling low K signaling pathway. Arrowhead line, positive regulation; bar-head lines, negative regulation; gray color, previously identified; black color, identified in this study. doi:10.1371/journal.pone.0047797.ggrown under +K conditions for 4 days and then transferred and grown on +K or 2K medium for 12 days. Length of primary roots were analyzed (n.30). Significant differences were represented by different letters on the bars (P,0.05; t-test). (JPG)Table S1 CK content in K-deficient- and K-sufficient-grown WT plants. Measurement of CK content in roots and shoots under both +K and -K conditions. tZ, trans-zeatin; tZR, tZ riboside; cZ, cis-zeatin; cZR, cZ riboside; iP, N6-(D2-isopentenyl)adenine; iPR, iP riboside; DZ, dihydrozeatin; DZR, DZ riboside; tZ7G, tZ-7-N-glucoside; tZ9G, tZ-9-N-glucoside; tZOG, tZ-Oglucoside; tZROG, tZR-O-glucoside; cZOG, cZ-O-glucoside; cZROG, cZR-O-glucoside; DZ9G, DZ-9-N-glucoside; iP7G, iP7-N-glucoside; iP9G, iP-9 -N -glucoside; tZRPs, tZR phosphates; cZRPs, cZR phosphates; iPRPs, iPR phosphates; DZRPs, DZR phosphates; cZRPOG, cZR phosphate-O-glucoside; tZRPOG, tZR phosphate-O-glucoside (n.6). (XLS)AcknowledgmentsWe thank Dr. T Kakimoto (Osaka University) for providing the ahk and ipt1,3,5,7 mutant seeds and Dr. W. Gruissem (ETH Zurich) for the IPT3ox seed.Supporting InformationFigure S1 Root growth assay of WT, IPT3-ox, ipt1,3,5,and ahk2ahk3 under +K and -K conditions. (A) WT, IPT3ox, ipt1,3,5,7 and ahk2ahk3 grown under +K and 2K conditions for 7 days. (B) Root growth assay of WT, IPT3-ox and ipt1,3,5,7 plants under +K and 2K conditions for 12 days. Plants wereAuthor ContributionsConceived and designed the experiments: YN LPT RS. Performed the experiments: YN MK RS. Analyzed the data: YN LPT HS RN RS. Wrote the paper: RN LPT RS.Cytokinins Regulate Low K Signaling
Insects can recognize a variety of plant compounds that stimulate specific behaviors, such as feeding and egg laying (oviposition) by chemoreceptive organs [1?]. It is well known that some insects lay eggs on their host plants, and the oviposition behavior is induced by the recognition of the plant components with sensilla on these chemoreceptive organs [5?], But the detailed mechanism of this identification is not clear. Chemosensory proteins (CSPs) are a class of small (10?5 kDa).Accordance with their function, CK levels were decreased in WT plants under K-deficient conditions (Figure 1), whereas ABA levels increased [30]. Taken together, we propose a model in which plants adapt to K deprivation by triggering an efficient regulation of various hormonal biosynthesis and signal cascades, including CKs and CK signaling (Figure 6) [7,12,13,30]. Specifically, for CKs and CK signaling, we suggest that during K deprivation, CK metabolism is altered, leading to a decrease in CKs. 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.Figure 6. A schematic model for the roles of CKs in low K signal pathway. Low K conditions lead to reduced levels of endogenous CKs, which are negative regulators under these conditions. Lower CK levels result in ROS production, HAK5 expression, and then altered root growth. Previous studies showed that ethylene is a positive regulator in low K signaling that controls ROS production, HAK5 expression as well as root hair growth [13]. ABA [30] and auxin [12] also are involved in controlling low K signaling pathway. Arrowhead line, positive regulation; bar-head lines, negative regulation; gray color, previously identified; black color, identified in this study. doi:10.1371/journal.pone.0047797.ggrown under +K conditions for 4 days and then transferred and grown on +K or 2K medium for 12 days. Length of primary roots were analyzed (n.30). Significant differences were represented by different letters on the bars (P,0.05; t-test). (JPG)Table S1 CK content in K-deficient- and K-sufficient-grown WT plants. Measurement of CK content in roots and shoots under both +K and -K conditions. tZ, trans-zeatin; tZR, tZ riboside; cZ, cis-zeatin; cZR, cZ riboside; iP, N6-(D2-isopentenyl)adenine; iPR, iP riboside; DZ, dihydrozeatin; DZR, DZ riboside; tZ7G, tZ-7-N-glucoside; tZ9G, tZ-9-N-glucoside; tZOG, tZ-Oglucoside; tZROG, tZR-O-glucoside; cZOG, cZ-O-glucoside; cZROG, cZR-O-glucoside; DZ9G, DZ-9-N-glucoside; iP7G, iP7-N-glucoside; iP9G, iP-9 -N -glucoside; tZRPs, tZR phosphates; cZRPs, cZR phosphates; iPRPs, iPR phosphates; DZRPs, DZR phosphates; cZRPOG, cZR phosphate-O-glucoside; tZRPOG, 
tZR phosphate-O-glucoside (n.6). (XLS)AcknowledgmentsWe thank Dr. T Kakimoto (Osaka University) for providing the ahk and ipt1,3,5,7 mutant seeds and Dr. W. Gruissem (ETH Zurich) for the IPT3ox seed.Supporting InformationFigure S1 Root growth assay of WT, IPT3-ox, ipt1,3,5,and ahk2ahk3 under +K and -K conditions. (A) WT, IPT3ox, ipt1,3,5,7 and ahk2ahk3 grown under +K and 2K conditions for 7 days. (B) Root growth assay of WT, IPT3-ox and ipt1,3,5,7 plants under +K and 2K conditions for 12 days. Plants wereAuthor ContributionsConceived and designed the experiments: YN LPT RS. Performed the experiments: YN MK RS. Analyzed the data: YN LPT HS RN RS. Wrote the paper: RN LPT RS.Cytokinins Regulate Low K Signaling
Insects can recognize a variety of plant compounds that stimulate specific behaviors, such as feeding and egg laying (oviposition) by chemoreceptive organs [1?]. It is well known that some insects lay eggs on their host plants, and the oviposition behavior is induced by the recognition of the plant components with sensilla on these chemoreceptive organs [5?], But the detailed mechanism of this identification is not clear. Chemosensory proteins (CSPs) are a class of small (10?5 kDa).
