Cytokinin N-glucosides: Occurrence, Metabolism and Biological Activities in Plants

Abstract

Cytokinins (CKs) are a class of phytohormones affecting many aspects of plant growth and development. In the complex process of CK homeostasis in plants, N-glucosylation represents one of the essential metabolic pathways. Its products, CK N7- and N9-glucosides, have been largely overlooked in the past as irreversible and inactive CK products lacking any relevant physiological impact. In this work, we report a widespread distribution of CK N-glucosides across the plant kingdom proceeding from evolutionary older to younger plants with different proportions between N7- and N9-glucosides in the total CK pool. We show dramatic changes in their profiles as well as in expression levels of the UGT76C1 and UGT76C2 genes during Arabidopsis ontogenesis. We also demonstrate specific physiological effects of CK N-glucosides in CK bioassays including their antisenescent activities, inhibitory effects on root development, and activation of the CK signaling pathway visualized by the CK-responsive YFP reporter line, TCSv2::3XVENUS. Last but not least, we present the considerable impact of CK N7- and N9-glucosides on the expression of CK-related genes in maize and their stimulatory effects on CK oxidase/dehydrogenase activity in oats. Our findings revise the apparent irreversibility and inactivity of CK N7- and N9-glucosides and indicate their involvement in CK evolution while suggesting their unique function(s) in plants.

Desiccation as a Post-maturation Treatment Helps Complete Maturation of Norway Spruce Somatic Embryos: Carbohydrates, Phytohormones and Proteomic Status

“…Despite this, the hormonal spectra mostly corresponded with those in M5 embryos, especially in the case of ABA derivatives and auxins. However, in contrast to SEs, ZEd also contained cytokinin N -glucosides ( N9 - but not N7 -glucosides), apparently irreversible forms widely distributed throughout the plant kingdom ( Pokorná et al, 2021 ). Very low concentrations of phytohormones in Norway spruce ZEd suggest a possible correlation between the minimum WC in these winter seeds and their low biochemical activity, which seems to be related to the deep dormancy of Norway spruce seeds during the winter season.…”

Hormonome Dynamics During Microgametogenesis in Different Nicotiana Species

“…The absence of DZ-types has also been observed in anthers of rice (Hirano et al, 2008), and the lack of these CK-types appears to be characteristic of some evolutionarily older non-vascular plants (e.g., Stirk et al, 2003;Záveská Drábková et al, 2015;Žižková et al, 2017). In Arabidopsis seedlings, Hošek et al (2020) showed that DZtype CKs are metabolically independent of other CK metabolic pathways, indicating their low abundance (e.g., Pokorná et al, 2021) compared with iP-or tZ-types, which might also be related to tobacco pollen.…”

Diverse Effect of Two Cytokinins, Kinetin and Benzyladenine, on Plant Development, Biotic Stress Tolerance, and Gene Expression

“…Both benzyladenine and kinetin are adenine-type cytokinins with a similar chemical structure, but in BA, a benzyl group can be found instead of the furfuryl group. It is noteworthy that senescence was delayed by kinetin and BA in an oat leaf test, but not by natural cytokinins, zeatin, and isopentenyl adenine [8]. In addition, both benzyladenine and kinetin show antioxidant properties in human skin fibroblast and in mammalian cells [9,10].…”