Phytohormones are naturally occurring secondary metabolites that regulate plant responses, including development, growth, reproduction, and responses to biotic and abiotic stresses. The analysis of phytohormones is challenging, as they comprise a range of structurally diverse compounds with different chemistries, are labile, and are present in highly complex plant matrices at very low concentrations (10-9 M to 10-6 M)1.
Recognized plant hormones include ethylene, auxin, abscisic acid, salicylates, jasmonates, cytokinins, gibberellins, strigolactones, nitric oxide and brassinosteroids. While each class of hormones has characteristic biological activities, accumulating evidence suggests extensive cross-talk among the hormone classes, resulting in a signalling network that modulates multiple hormonal and metabolic systems. Examples include the roles of auxins and gibberellins in growth regulation, cytokinins, auxins, abscisic acid and strigolactones in apical dominance, and salicylates, jasmonates and auxin in plant responses to pathogens2. Therefore the investigation of phytohormones controlling specific development pathways, defence activation and physiological responses requires the ability to quantify multiple classes of phytohormones from a single experimental sample.
We have developed a plant hormone analysis platform utilising ultra-performance liquid chromatography tandem-mass spectrometry (UPLC/ESI-MS/MS) with multiple reaction monitoring (MRM) to measure multiple members of the major classes of phytohormones, including auxins, abscisic acid, salicylates, jasmonates, cytokinins, gibberellins and related metabolites, in a single plant extract.
This platform is being used for the analysis of phytohormones in different tissues types from complex plant matrices such as kiwifruit, avocado and apple, as well as simpler model plants matrices such as Medicago truncatula. Examples will be given which contribute to a better understanding of plant defence mechanisms to disease in resistant and susceptible kiwifruit cultivars, and in the regulation of plant growth and fruit size in kiwifruit, avocado, apple and model plant systems.