scholarly journals Differential Subcellular Distribution of Cytokinins: How Does Membrane Transport Fit into the Big Picture?

2021 ◽  
Vol 22 (7) ◽  
pp. 3428
Author(s):  
Daniel Nedvěd ◽  
Petr Hošek ◽  
Petr Klíma ◽  
Klára Hoyerová
Keyword(s):  
Membrane Transport ◽  
Nucleoside Transporters ◽  
Long Distance ◽  
Cytokinin Biosynthesis ◽  
Signalling Molecules ◽  
Equilibrative Nucleoside Transporters ◽  
Physiological Processes ◽  
Big Picture ◽  
Membrane Bound ◽  
Related Compounds

Cytokinins are a class of phytohormones, signalling molecules specific to plants. They act as regulators of diverse physiological processes in complex signalling pathways. It is necessary for plants to continuously regulate cytokinin distribution among different organs, tissues, cells, and compartments. Such regulatory mechanisms include cytokinin biosynthesis, metabolic conversions and degradation, as well as cytokinin membrane transport. In our review, we aim to provide a thorough picture of the latter. We begin by summarizing cytokinin structures and physicochemical properties. Then, we revise the elementary thermodynamic and kinetic aspects of cytokinin membrane transport. Next, we review which membrane-bound carrier proteins and protein families recognize cytokinins as their substrates. Namely, we discuss the families of “equilibrative nucleoside transporters” and “purine permeases”, which translocate diverse purine-related compounds, and proteins AtPUP14, AtABCG14, AtAZG1, and AtAZG2, which are specific to cytokinins. We also address long-distance cytokinin transport. Putting all these pieces together, we finally discuss cytokinin distribution as a net result of these processes, diverse in their physicochemical nature but acting together to promote plant fitness.

scholarly journals Recent advances in studies on biochemical and structural properties of equilibrative and concentrative nucleoside transporters.

2005 ◽  
Vol 52 (4) ◽  
pp. 749-758 ◽  
Author(s):  
Marzena Podgorska ◽  
Katarzyna Kocbuch ◽  
Tadeusz Pawelczyk
Keyword(s):  
Mammalian Cells ◽  
Cell Function ◽  
De Novo ◽  
Transport Processes ◽  
Nucleoside Transporters ◽  
Membrane Topology ◽  
Nucleoside Transporter ◽  
Signalling Molecules ◽  
Physiological Processes ◽  
Carrier Mediated Transport

Nucleoside transporters (NT) facilitate the movement of nucleosides and nucleobases across cell membranes. NT-mediated transport is vital for the synthesis of nucleic acids in cells that lack de novo purine synthesis. Some nucleosides display biological activity and act as signalling molecules. For example, adenosine exerts a potent action on many physiological processes including vasodilatation, hormone and neurotransmitter release, platelet aggregation, and lipolysis. Therefore, carrier-mediated transport of this nucleoside plays an important role in modulating cell function, because the efficiency of the transport processes determines adenosine availability to its receptors or to metabolizing enzymes. Nucleoside transporters are also key elements in anticancer and antiviral therapy with the use of nucleoside analogues. Mammalian cells possess two major nucleoside transporter families: equilibrative (ENT) and concentrative (CNT) Na(+)-dependent ones. This review characterizes gene loci, substrate specificity, tissue distribution, membrane topology and structure of ENT and CNT proteins. Regulation of nucleoside transporters by various factors is also presented.

scholarly journals Testicular disposition of clofarabine in rats is dependent on equilibrative nucleoside transporters

2021 ◽  
Vol 9 (4) ◽  
Author(s):  
Siennah R. Miller ◽  
Joseph L. Jilek ◽  
Meghan E. McGrath ◽  
Raymond K. Hau ◽  
Erin Q. Jennings ◽  
...  
Keyword(s):  
Nucleoside Transporters ◽  
Equilibrative Nucleoside Transporters

scholarly journals Potyviral 6K2 Protein Long-Distance Movement and Symptom-Induction Functions Are Independent and Host-Specific

2004 ◽  
Vol 17 (5) ◽  
pp. 502-510 ◽  
Author(s):  
Carl Spetz ◽  
Jari P. T. Valkonen
Keyword(s):  
Spontaneous Mutation ◽  
Systemic Infection ◽  
Wild Type ◽  
Virus Propagation ◽  
Long Distance ◽  
Potato Virus A ◽  
Viral Mutant ◽  
Membrane Bound ◽  
Long Distance Movement

Deletion of various portions, or insertion of six histidine residues (6×His) into various positions of the membrane-bound 6K2 protein (53 amino acids) of Potato virus A (PVA, genus Potyvirus), inhibited systemic infection in Nicotiana tabacum and N. benthamiana plants. However, a spontaneous mutation (Gly2Cys) that occurred in 6K2 adjacent to the 6×His insert placed between Ser1 and Gly2 enabled systemic infection in a single N. benthamiana plant. No symptoms were observed, but virus titers were similar to the symptom-inducing wild-type (wt) PVA. N. tabacum plants were not systemically infected, albeit virus propagation was observed in inoculated protoplasts. The 6×His/Gly2Cys mutant was reconstructed in vitro and serially propagated by mechanical inoculation in N. benthamiana. Following the third passage, a novel viral mutant appeared, lacking the last four His residues of the insert, as well as the Gly2 and Thr3 of 6K2. It infected N. tabacum plants systemically, and in the systemically infected N. benthamiana leaves, vein chlorosis and mild yellowing symptoms were observed, typical of wt PVA infection. The mutant virus accumulated to titers similar to wt PVA in both hosts. These results show that the PVA 6K2 protein affects viral long-distance movement and symptom induction independently and in a host-specific manner.

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