Auxin cytokinin

Most species of angiosperms produce hermaphroditic flowers. The unisexuality in some plants most often results from developmentally programmed abortion or selective reduction in sex organ primordia. In dicots, higher levels of auxins, cytokinins, and ethylene usually correlate with female sex expression and in most of them the femaleness is mainly promoted by ethylene. ... 

Plant cell synthesizes auxins, cytokinins, opines tumor forms. 

There also have been clear indications that interactions of ethylene with auxins, cytokinins, gibberellins and ABA are involved in both ethylene production and action. Generally the effects of ethylene tend to antagonize those of auxins, cytokinins and gibberellins, and tend to reinforce those of ABA, depending, however, on tissue systems involved. Reinforcement of ethylene by ABA and vice versa occurs more frequently in senescence. 

Auxin, cytokinin, and other unknown substances are thought to regulate apical dominance.482 Application of cytokinin or overexpression of the 1PTgene shows a phenotype with a reduction in apical dominance.404 483 484 Arabidopsis mutants with increased levels of cytokinin also show reduced apical dominance 485-487 These results suggest that cytokinins play a role in the promotion of bud outgrowth. 

No significant effects were observed on auxin, cytokinin or gibbereilin induced cell expansion. Photosynthesis, respiration, RNA synthesis and protein synthesis were uneffected at concentrations where the plant cell division is strongly inhibited. 

A final exciting approach is to introduce into plants the genes for overproduction of a hormone, or antisense genes for an enzyme involve in hormone synthesis. These transgenic plants have already provided us with important information about the biological roles of auxins, cytokinins and ethylene [32]. 

In order to improve yields and productivities of secondary metabolites in plant cell culture s it is essential the selection of the most elEcient plant growth regulators (auxins, cytokinins, gibberellic acid and abscicic acid) and the relationship between diem [74, 75]. 

O. have been shown to inhibit flowering, promote vegetative growth and control organ development in plant tissue culture. Effective concentrations of O. are 100-1000-fold lower than those of other plant hormones, such as auxins, cytokinins and gibberellins. 

Clearly, in the case of gametophore formation for which auxin, cytokinin and light at a relatively high level are all required (> 16 jumol m s of MRL for maximal production in the absence of exogenous cytokinin [Jenkins and Cove,... 

Ferguson B J, Beveridge CA (2009) Roles for auxin, cytokinin and strigolactone in regulating shoot branching. Plant Physiol 149 1929-1944. doi 10.1104/pp. 109.135475... 

The response of many types of stem and hypocotyl cells to auxin is biphasic (Vanderhoef and Stahl 1975). The initial phase of the response is similar to growth which can be induced by low pH, while the second phase has properties identical to the thoroughly studied long-term auxin response. Cytokinins inhibit the second phase of the auxin response, but have no effect on the early phase. The response of coleoptile segments to auxin is not so distinctly biphasic, and treatment with cytokinins cannot be used to inhibit selectively the initial phase of the auxin response (Evans 1976 a). This indicates a difference in the nature of the auxin response in dicots and monocots, or at least a difference in the nature of auxin/cytokinin interaction in these two groups. 

Thompson NP, Jacobs WP (1966) Polarity of lAA effect on sieve-tube and xylem regeneration in Coleus and tomato stems. Plant Physiol 41 673-682 Torrey JG (1953) The effect of certain metabolic inhibitors on vascular tissue differentiation in isolated pea roots. Am J Bot 40 525-533 Torrey JG, Loomis RS (1967) Auxin-cytokinin control of secondary vascular tissue formation in isolated roots of Raphanus. Am J Bot 54 1098-1106 Torrey JG, Fosket DE, Hepler PK (1971) Xylem formation A paradigm of cyto-differen-tiation in higher plants. Am Sci 59 338-352... 

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