Limitation of Cytokinin Export to the Shoots by Nucleoside Transporter ENT3 and Its Linkage with Root Elongation in Arabidopsis

Abstract

The trans-membrane carrier AtENT3 is known to transport externally supplied cytokinin ribosides and thus promote uptake by cells. However, its role in distributing either exogenous or endogenous cytokinins within the intact plant has not hitherto been reported. To test this, we used ent3-1 mutant Arabidopsis seedlings in which the gene is not expressed due to a T-DNA insertion, and examined the effect on the concentration and distribution of either endogenous cytokinins or exogenous trans-zeatin riboside applied to the roots. In the mutant, accumulation of endogenous cytokinins in the roots was reduced and capacity to deliver externally supplied trans-zeatin riboside to the shoots was increased suggesting involvement of equilibrative nucleoside (ENT) transporter in the control of cytokinin distribution in the plants. Roots of ent3-1 were longer in the mutant in association with their lower cytokinin concentration. We concluded that the ENT3 transporter participates in partitioning endogenous cytokinins between the apoplast and the symplast by facilitating their uptake by root cells thereby limiting cytokinin export to the shoots through the xylem. Dilution of the mineral nutrient solution lowered endogenous cytokinin concentration in the roots of both wild type (WT) and ent3-1 plants accompanied by promotion of root elongation. Nevertheless, cytokinin content was lower, while roots were longer in the ent3-1 mutant than in the WT under either normal or deficient mineral nutrition suggesting a significant role of ENT3 transporter in the control of cytokinin level in the roots and the rate of their elongation.

Effects of Phytohormone-Producing Rhizobacteria on Casparian Band Formation, Ion Homeostasis and Salt Tolerance of Durum Wheat

“…Extract separated by filtration was evaporated to an aqueous residue and divided into two parts for determination of cytokinins and indoleacetic acid (IAA, a hormone from the class of auxins). Cytokinins from the aqueous residue after their concentration on a C-18 cartridge (Waters Corporation, Milford, MA, USA) were separated by thin layer chromatography as previously described [ 31 ]. Contents of zeatin, its riboside and nucleotide in the corresponding chromatographic zones were determined by enzyme-linked immunosorbent assay (ELISA) using antibodies against zeatin riboside [ 32 ].…”

Dynamic cytokinin signalling landscapes during lateral root formation in Arabidopsis

“…azg2 roots had a slightly increased number of Stages VI to VIII LRP compared to control plants, but this difference was not significant (Tessi et al, 2021a). With regard to the ENT family, ENT3 and ENT6 could participate in CK riboside transport, with both genes being expressed in the root vasculature (Hirose et al, 2008;Korobova et al, 2021). Finally, naturally occurring CKs possess relatively hydrophobic side-chains and their diffusion from the cytoplasm to the apoplast cannot be ruled out (Nedved et al, 2021).…”

Nitric oxide and cytokinin cross-talk and their role in plant hypoxia response

“…Furthermore, members of the EQUILIBRATIVE NUCLEOSIDE TRANSPORTER (ENT) family, which are known to transport purine and pyrimidine nucleosides, may also act as influx carriers for CKs. 51 , 68 , 71 , 78 , 79 Although an ent1 mutation does not affect the CK response substantially, the ent3 mutant shows a reduced endogenous level of CKs in the roots. Surprisingly, this mutant also shows an enhanced capacity to deliver externally supplied tZ riboside to the shoot, which indicates that the ENT3 transporter might be involved in the CK distribution in plants.…”