The present paper introduces a highly sensitive and selective method for simultaneous quantification of 12 cytokinins (free form and their conjugates). The method includes a protocol of extraction with methanol/water/formic acid (15/4/1, v/v/v) to the micro-scale samples, pre-purification with solid phase extraction (SPE) cartridges of the extracts, separation with a high performance liquid chromatography (HPLC) and detection by an electrospray ionization ion trap mass spectrometry (ESI-Ion trap-MS) system in a consecutive ion monitoring (CRM) mode at the three stage fragmentation of mass spectrometry (MS³). The lowest detection level of the cytokinins of the method reaches 0.1–2.0 pg with a very wide range of linear regression from 1–512 pg, at the coefficient factors of 0.98–0.99. The feasibility of this method has been proven in the application of the method to the analysis of the trace-amount contents of cytokinins in the micro-scale samples of various types of plant materials, such as aerial parts of rice and poplar leaves etc. 12 endogenous cytokinins had been identified and quantified in the plant tissues, with an acceptable relatively higher recovery rate from 40% to 70%.

Chen W, Gai Y, Liu S, Wang R, Jiang X (2010) Quantitative analysis of cytokinins in plants by high performance liquid chromatography: electronspray ionization ion trap mass spectrometry. J. Integr. Plant Biol. 52(10), 925–932.

When it was discovered in the 1970s as a ubiquitous protein, ubiquitin, a 76-aminoacid peptide, had no assigned function. It was not until later that ubiquitin was found to be a necessary cofactor in a vital cellular process: the degradation of proteins. Work by Avram Hershko, Aaron Ciechanover, and Irwin Rose (for which they received the 2004 Nobel Prize in Chemistry) showed that the covalent attachment of ubiquitin provide proteins with a tag that dispatches them to the proteasome, the main cell degradation machinery.