GC-MS Methods for Cytokinins and Metabolites

Abstract

Cytokinin is a generic term proposed to define both naturally occurring and synthetic compounds that induce cell division in plant tissue cultures (e.g., tobacco stem pith, soybean cotyledonary callus and carrot secondary phloem etc.) grown on defined medium in the presence of an optimal concentration of auxin. Although the idea that specific chemical substances may control cell division in plants dates back to the nineteenth century (Wiesner 1892), it first received experimental support only in the early 1920’s following the observation that wounding induced cell division in many plant tissues, e.g., potato parenchyma (Haberlandt 1921). Kinetin (Fig. 1) was the first cytokinin to be identified, and its isolation in 1956 from autoclaved herring sperm DNA was a direct consequence of studies on growth requirements of plant tissue cultures (Miller et al. 1956). It does not occur per se in living tissues, and had resulted as an artefact of the autoclaving process in the original work. Synthetic kinetin was found to be a very potent promoter of cell division, and induced cell division activity in the tobacco pith assay at concentrations as low as 1 μg 1 ⁻¹. The realization that the kinetin effect could be replaced by extracts from many plant tissues triggered the search for endogenous cytokinins, resulting in the isolation of the first natural cytokinin, zeatin [6-(4-hydroxy-3-methylbut-trans-2-enylamino) purine] from immature Zea mays kernels (Letham 1963; Letham et al. 1964, 1967). The number of cytokinins identified so far from diverse natural sources is nearing 30. In addition to their occurrence as free compounds in higher plants, cytokinins have also been isolated from transfer ribonucleic acid (tRNA) hydrolysates of plants, animals and microorganisms (Letham and Wettenhall 1977; Letham and Palni 1983).