Nitrogen nutrients are known to increase the cytokinin content in plant roots and xylem sap. We found that regulation of IPT expression by nitrate and/or glutamine-related signals is responsible for the phenomenon(),), indicating that nitrogen-responsive cytokinins that burst in the root is regulated at the initial step of biosynthesis. These results support the role of cytokinin in long-distance nitrogen signaling (),).
Cytokinin is also synthesized by phytopathogenic bacteria, such as , and is a key factor in some plant diseases. infects plants and induces the formation of tumors by integrating the transferred-DNA (T-DNA) region of the Ti-plasmid into the plant nuclear genome. Tumors are formed because the T-DNA encodes enzymes that modify the synthesis of two plant growth hormones, auxin and cytokinin. We had demonstrated that a cytokinin biosynthesis enzyme, Tmr, which is encoded by the T-DNA region, is targeted to plastids of infected plant cells, and increases cytokinin production by modifying the biosynthetic pathway in the host plant（),().
Cytokinin Signaling in Arabidopsis | Plant Cell
Although there is a long history of cytokinin research from biological and agronomic perspectives that has provided a wealth of knowledge about plant development and plant-microbe interactions, understanding the structural basis for the reaction mechanism, substrate specificity, and evolution of cytokinin biosynthesis has been lacking. We have determined crystal structures of Tzs from , complexed with a natural substrate or its analogue (). The structures provide a structural insight into the reaction mechanism and unique evolution of cytokinin biosynthesis. A structure-based mutagenesis study of Tzs was used to identify the crucial amino acid residues that determine prenyl-donor substrate specificity differences between Tzs and higher-plant IPTs.
pathway, response to cytokinin ..
Interestingly, auxin mediates a very rapid negative control of the cytokinin pool by mainly suppressing the biosynthesis via the isopentenyladenosine-5'-monophosphate-independent pathway.
: Cytokinin biosynthesis in nodule initiation
In contrast, the effect of cytokinin overproduction on the entire auxin pool in the plant was slower, indicating that this most likely is mediated through altered development.
Auxin regulation of cytokinin biosynthesis in …
In addition, we were able to confirm that the lateral root meristems are likely to be the main sites of isopentenyladenosine-5'-monophosphate-dependent cytokinin synthesis, and that the aerial tissue of the plant surprisingly also was a significant source of cytokinin biosynthesis.
Auxin Regulation of Cytokinin ..
Our demonstration of shoot-localized synthesis, together with data demonstrating that auxin imposes a very rapid regulation of cytokinin biosynthesis, illustrates that the two hormones can interact also on the metabolic level in controlling plant development, and that the aerial part of the plant has the capacity to synthesize its own cytokinin independent of long-range transport from the root system.
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The Cytokinin Side Chain Commands Shooting: …
A functional shift from photosynthesis to resource mobilization in senescing leaves significantly contributes to the optimization of resource utilization by the whole plant.