Cytokinin
[2] The idea of specific substances required for cell division to occur in plants actually dates back to the Swiss physiologist J. Wiesner, who, in 1892, proposed that initiation of cell division is evoked by endogenous factors, indeed a proper balance among endogenous factors.
[8] In 1941, Johannes Van Overbeek found that the milky endosperm of immature coconut also had this factor, which stimulated cell division and differentiation in very young Datura embryos.
[11][12] Miller and his co-workers (1954) isolated and purified the cell division substance in crystallised form from autoclaved herring fish sperm DNA.
Later on, the generic name kinin was suggested to include kinetin and other substances having similar properties.
[13] Cytokinins are involved in many plant processes, including cell division and shoot and root morphogenesis.
Cytokinin moves from the roots into the shoots, eventually signaling lateral bud growth.
When cytokinin and auxin are present in equal levels, the parenchyma cells form an undifferentiated callus.
Production of cytokinins by Pseudomonas fluorescens G20-18 has been identified as a key determinant to efficiently control the infection of A. thaliana with P. syringae..[17] While cytokinin action in vascular plants is described as pleiotropic, this class of plant hormones specifically induces the transition from apical growth to growth via a three-faced apical cell in moss protonema.
This pathway is initiated by cytokinin binding to a histidine kinase receptor in the endoplasmic reticulum membrane.
The phosphotransfer proteins can then phosphorylate the type-B response regulators (RR) which are a family of transcriptions factors.
[22] Because cytokinins promote plant cell division and growth, they have been studied since the 1970s as potential agrochemicals, however they have yet to be widely adopted, probably due to the complex nature of their effects.
[23] One study found that applying cytokinin to cotton seedlings led to a 5–10% increase in yield under drought conditions.
