Cytokinin Translocation to, and Biosynthesis and Metabolism within, Cereal and Legume Seeds: Looking Back to Inform the Future

Abstract

Early in the history of cytokinins, it was clear that Zea mays seeds contained not just trans-zeatin, but its nucleosides and nucleotides. Subsequently, both pods and seeds of legumes and cereal grains have been shown to contain a complex of cytokinin forms. Relative to the very high quantities of cytokinin detected in developing seeds, only a limited amount appears to have been translocated from the parent plant. Translocation experiments, and the detection of high levels of endogenous cytokinin in the maternal seed coat tissues of legumes, indicates that cytokinin does not readily cross the maternal/filial boundary, indicating that the filial tissues are autonomous for cytokinin biosynthesis. Within the seed, trans-zeatin plays a key role in sink establishment and it may also contribute to sink strength. The roles, if any, of the other biologically active forms of cytokinin (cis-zeatin, dihydrozeatin and isopentenyladenine) remain to be elucidated. The recent identification of genes coding for the enzyme that leads to the biosynthesis of trans-zeatin in rice (OsCYP735A3 and 4), and the identification of a gene coding for an enzyme (CPN1) that converts trans-zeatin riboside to trans-zeatin in the apoplast, further cements the key role played by trans-zeatin in plants.

Cytokinin acts as a systemic signal coordinating reproductive effort in Arabidopsis

“…We next asked whether cytokinin is also transported into emerging fruits. Developing seeds are among the tissues with the highest cytokinin levels, and cytokinins are key regulators of the seed size and number 27,33,34 . While it is well established that cytokinin biosynthesis occurs in developing seeds, the contribution of transport from maternal tissues has been less explored 27 .…”

“…Developing seeds are among the tissues with the highest cytokinin levels, and cytokinins are key regulators of the seed size and number 27,33,34 . While it is well established that cytokinin biosynthesis occurs in developing seeds, the contribution of transport from maternal tissues has been less explored 27 . To address this question, we analyzed plants deficient in cytokinin long-distance transport mediated by ATP-binding cassette transporter subfamily G14 (ABCG14) 35,36 .…”

High- or Low-Yielding F2 Progeny of Wheat Is Result of Specific TaCKX Gene Coexpression Patterns in Association with Grain Yield in Paternal Parent

“…The cytokinin content in plant organs is regulated mainly by metabolic processes, as well as their transport [ 11 , 12 , 13 ]. The predominant role in metabolic processes is played by the irreversible degradation of cytokinins by CKX enzymes, which can regulate rice grain yield [ 14 , 15 , 16 , 17 ].…”