CYTOKININS: Activity, Biosynthesis, and Translocation

Abstract

Cytokinins (CKs) play a crucial role in various phases of plant growth and development, but the basic molecular mechanisms of their biosynthesis and signal transduction only recently became clear. The progress was achieved by identifying a series of key genes encoding enzymes and proteins controlling critical steps in biosynthesis, translocation, and signaling. Basic schemes for CK homeostasis and root/shoot communication at the whole-plant level can now be devised. This review summarizes recent findings on the relationship between CK structural variation and activity, distinct features in CK biosynthesis between higher plants and Agrobacterium infected plants, CK translocation at whole-plant and cellular levels, and CKs as signaling molecules for nutrient status via root-shoot communication.

Arabidopsis ABCG14 protein controls the acropetal translocation of root-synthesized cytokinins

“…Cytokinins can act as autocrine, paracrine or long-distance signals 1,10 , and different types of cytokinins are synthesized and distributed in distinct tissues or cell types. Several cytokinin biosynthetic genes are found mainly expressed in the root, for instance, AtIPT1 and AtIPT7 are primarily expressed in the vascular stele of the elongation zone and/or root phloem companion cells, indicating that these sites are major sources of root-derived cytokinins 33 .…”

“…C ytokinins are a heterogeneous class of N 6 -substituted adenine derivatives with either an isoprene-derived or an aromatic side chain [1][2][3] . Since their discovery in the 1950s as key promoters of cell division in plants, a plethora of biological functions have been attributed to these signalling molecules, encompassing the regulation of cell division and differentiation 4 , chloroplast development 5 , leaf senescence 5,6 , root-and shootapical dominance 7 , nutrient balances and stress responses 8 .…”

“…Isoprenoid cytokinins, including trans-zeatin (tZ), dihydrozeatin (DHZ), cis-zeatin (cZ) and isopentenyladenine (iP), are the most abundant species in higher plants 1 . Chemical profiling of xylem and phloem sap, and reciprocal grafting of roots and shoots of cytokinin-deficient mutants revealed that tZ-type cytokinins are mainly synthesized in roots, and iP-type cytokinins mainly in shoots.…”

Biological differences that distinguish the 2 major stages of wound healing in potato tubers

“…16 Wound-responding tuber tissue has been found to produce less than quantifiable amounts of active CK, but leaves behind quantitative amounts of both precursors and catabolic products of active CK. 4 These results suggest that the required amount of biologically active CKs are modulated to be extremely low and not persistent even at minute levels in tuber tissue during WPF.…”

Cytokinin signaling regulates pavement cell morphogenesis in Arabidopsis

“…At the cellular level, cytokinin is known to promote cell division, stem-cell specification, and chloroplast biogenesis [9][10][11][12]. The major cytokinin biosynthetic pathway is mediated by adenosine phosphate-isopentenyltransferase (IPT), which catalyzes the first and rate-limiting step [13,14]. The structural diversity of natural cytokinins and modifications of the adenine moiety confer specificity of the cytokinin receptor interaction [14].…”