Ligand-binding properties and subcellular localization of maize cytokinin receptors
Open Access
- 21 July 2011
- journal article
- research article
- Published by Oxford University Press (OUP) in Journal of Experimental Botany
- Vol. 62 (14), 5149-5159
- https://doi.org/10.1093/jxb/err220
Abstract
The ligand-binding properties of the maize (Zea mays L.) cytokinin receptors ZmHK1, ZmHK2, and ZmHK3a have been characterized using cytokinin binding assays with living cells or membrane fractions. According to affinity measurements, ZmHK1 preferred N6-(Δ2-isopentenyl)adenine (iP) and had nearly equal affinities to trans-zeatin (tZ) and cis-zeatin (cZ). ZmHK2 preferred tZ and iP to cZ, while ZmHK3a preferred iP. Only ZmHK2 had a high affinity to dihydrozeatin (DZ). Analysis of subcellular fractions from leaves and roots of maize seedlings revealed specific binding of tZ in the microsome fraction but not in chloroplasts or mitochondria. In competitive binding assays with microsomes, tZ and iP were potent competitors of [3H]tZ while cZ demonstrated significantly lower affinity; adenine was almost ineffective. The binding specificities of microsomes from leaf and root cells for cytokinins were consistent with the expression pattern of the ZmHKs and our results on individual receptor properties. Aqueous two-phase partitioning and sucrose density-gradient centrifugation followed by immunological detection with monoclonal antibody showed that ZmHK1 was associated with the endoplasmic reticulum (ER). This was corroborated by observations of the subcellular localization of ZmHK1 fusions with green fluorescent protein in maize protoplasts. All these data strongly suggest that at least a part of cytokinin perception occurs in the ER.Keywords
This publication has 53 references indexed in Scilit:
- The Cytokinin Receptors of Arabidopsis Are Located Mainly to the Endoplasmic ReticulumPlant Physiology, 2011
- Environmental perception avenues: the interaction of cytokinin and environmental response pathwaysPlant, Cell & Environment, 2009
- Characterization of New Maize Genes Putatively Involved in Cytokinin Metabolism and Their Expression during Osmotic Stress in Relation to Cytokinin LevelsPlant Physiology, 2009
- Highly Sensitive and High-Throughput Analysis of Plant Hormones Using MS-Probe Modification and Liquid ChromatographyTandem Mass Spectrometry: An Application for Hormone Profiling in Oryza sativaPlant and Cell Physiology, 2009
- Plant Receptors Go Endosomal: A Moving View on Signal TransductionPlant Physiology, 2008
- Cytokinins in the Bryophyte Physcomitrella patens: Analyses of Activity, Distribution, and Cytokinin Oxidase/Dehydrogenase Overexpression Reveal the Role of Extracellular CytokininsPlant Physiology, 2007
- Two-component circuitry in Arabidopsis cytokinin signal transductionNature, 2001
- Relationship between the inhibition constant (KI) and the concentration of inhibitor which causes 50 per cent inhibition (I50) of an enzymatic reactionBiochemical Pharmacology, 1973
- Cleavage of Structural Proteins during the Assembly of the Head of Bacteriophage T4Nature, 1970
- A Revised Medium for Rapid Growth and Bio Assays with Tobacco Tissue CulturesPhysiologia Plantarum, 1962