Metabolite Profiling of Growth Regulatory Hormones from Maize Tissue

Plant regulatory small molecules, or phytohormones, are small regulatory metabolites in plants. Phytohormones regulate all aspects of plant growth and development. They include jasmonic acid, auxin, abscisic acid, salicylic acid, 1-aminocyclopropane-1-carboxylic acid, gibberellins, and brassinosteroids. Their activity is highly dependent on their concentration, and therefore accurate quantification is necessary to understand their biological role in regulating downstream targets. However, their low abundance results in low signal to noise ratios during detection. In addition, the chemical distinctions between the regulatory small molecule classes include a wide polarity range and differences in charge, which has previously prevented the simultaneous extraction and separation by chromatography of multiple regulatory small molecules. This review discusses the extraction of hormones from any maize tissue, followed by their purification and quantification, and the limitations of these approaches. Recent advancements in mass spectrometry and sample pretreatment have improved the sensitivity of techniques to accurately and simultaneously quantify multiple small regulatory plant hormones from maize tissue. These techniques should usher in a new era in which measurement of phytohormones will allow for more accurate evaluation of phytohormone roles in maize growth and development. We also highlight potential new plant regulatory hormones and discuss how the techniques described here may benefit future discovery of new classes of phytohormones.