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Plant membrane assays with cytokinin receptors underpin the unique role of free cytokinin bases as biologically active ligands.

Lomin SN, Krivosheev DM, Steklov MY, Arkhipov DV, Osolodkin DI, Schmülling T, Romanov GA - J. Exp. Bot. (2015)

Bottom Line: According to molecular modelling and docking studies, N (9)-ribosylation alters the bonding pattern in cytokinin-receptor interaction and prevents β6-β7 loop movement important for tight hormone binding.A common feature of all receptors was a greatly reduced ligand binding at low (5.0-5.5) pH.The particularly high sensitivity of ZmHK1 to pH changes leads to the suggestion that some cytokinin receptors may play an additional role as pH sensors in the lumen of the endoplasmic reticulum.

View Article: PubMed Central - PubMed

Affiliation: Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya 35, 127276 Moscow, Russia.

No MeSH data available.


Interaction of cytokinin ribosides and bases with receptors AHK3 and ZmHK1. Receptor–ligand interaction was measured in a plant (tobacco microsomes) or bacterial (E. coli spheroplasts) assay system as indicated. tZ, trans-zeatin; tZR, trans-zeatin riboside; iP, isopentenyladenine; iPR, isopentenyladenosine; NS and TB indicate non-specific and total binding, respectively.
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Figure 4: Interaction of cytokinin ribosides and bases with receptors AHK3 and ZmHK1. Receptor–ligand interaction was measured in a plant (tobacco microsomes) or bacterial (E. coli spheroplasts) assay system as indicated. tZ, trans-zeatin; tZR, trans-zeatin riboside; iP, isopentenyladenine; iPR, isopentenyladenosine; NS and TB indicate non-specific and total binding, respectively.

Mentions: Of special interest is the interaction of the receptors with cytokinin ribosides since data available in the literature are contradictory (Heyl et al., 2012). The affinity of two ubiquitous natural ribosides, trans-zeatin riboside (tZR) and isopentenyladenosine (iPR), for the receptors was tested and compared with that of the corresponding bases (Fig. 4). Competitive experiments with E. coli spheroplasts confirmed previous data (Romanov et al., 2005, 2006; Romanov and Lomin, 2009; Stolz et al., 2011): ribosides were able to displace labelled tZ from the hormone–receptor complex quite effectively and similarly to the corresponding cytokinin bases. However, in the plant assay system, ribosides behaved in a different way (Fig. 4): in most cases, the ribosides hardly competed with labelled tZ for binding to the receptors. The only exception was the ZmHK1–iPR interaction, although the affinity of the receptor for the ligand was at least two orders of magnitude lower than in the case of the ZmHK1–iP interaction. Supplemental assays with AHK4 corroborated the inability of cytokinin receptors to bind N9-ribosylated cytokinins with high affinity (Supplementary Fig. S3 at JXB online). Thus, in the case of cytokinin ribosides, the results of binding assays strongly depend on the test system.


Plant membrane assays with cytokinin receptors underpin the unique role of free cytokinin bases as biologically active ligands.

Lomin SN, Krivosheev DM, Steklov MY, Arkhipov DV, Osolodkin DI, Schmülling T, Romanov GA - J. Exp. Bot. (2015)

Interaction of cytokinin ribosides and bases with receptors AHK3 and ZmHK1. Receptor–ligand interaction was measured in a plant (tobacco microsomes) or bacterial (E. coli spheroplasts) assay system as indicated. tZ, trans-zeatin; tZR, trans-zeatin riboside; iP, isopentenyladenine; iPR, isopentenyladenosine; NS and TB indicate non-specific and total binding, respectively.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4378623&req=5

Figure 4: Interaction of cytokinin ribosides and bases with receptors AHK3 and ZmHK1. Receptor–ligand interaction was measured in a plant (tobacco microsomes) or bacterial (E. coli spheroplasts) assay system as indicated. tZ, trans-zeatin; tZR, trans-zeatin riboside; iP, isopentenyladenine; iPR, isopentenyladenosine; NS and TB indicate non-specific and total binding, respectively.
Mentions: Of special interest is the interaction of the receptors with cytokinin ribosides since data available in the literature are contradictory (Heyl et al., 2012). The affinity of two ubiquitous natural ribosides, trans-zeatin riboside (tZR) and isopentenyladenosine (iPR), for the receptors was tested and compared with that of the corresponding bases (Fig. 4). Competitive experiments with E. coli spheroplasts confirmed previous data (Romanov et al., 2005, 2006; Romanov and Lomin, 2009; Stolz et al., 2011): ribosides were able to displace labelled tZ from the hormone–receptor complex quite effectively and similarly to the corresponding cytokinin bases. However, in the plant assay system, ribosides behaved in a different way (Fig. 4): in most cases, the ribosides hardly competed with labelled tZ for binding to the receptors. The only exception was the ZmHK1–iPR interaction, although the affinity of the receptor for the ligand was at least two orders of magnitude lower than in the case of the ZmHK1–iP interaction. Supplemental assays with AHK4 corroborated the inability of cytokinin receptors to bind N9-ribosylated cytokinins with high affinity (Supplementary Fig. S3 at JXB online). Thus, in the case of cytokinin ribosides, the results of binding assays strongly depend on the test system.

Bottom Line: According to molecular modelling and docking studies, N (9)-ribosylation alters the bonding pattern in cytokinin-receptor interaction and prevents β6-β7 loop movement important for tight hormone binding.A common feature of all receptors was a greatly reduced ligand binding at low (5.0-5.5) pH.The particularly high sensitivity of ZmHK1 to pH changes leads to the suggestion that some cytokinin receptors may play an additional role as pH sensors in the lumen of the endoplasmic reticulum.

View Article: PubMed Central - PubMed

Affiliation: Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya 35, 127276 Moscow, Russia.

No MeSH data available.