Plant hormones, also known as phytohormones, are trace organic compounds synthesized within plants that play a crucial role in regulating various aspects of growth and development. These hormones are produced in specific tissues and can be transported to different parts of the plant, where they exert their effects at remarkably low concentrations. Their influence spans a wide array of processes, including cell division, elongation, differentiation, germination, rooting, flowering, fruiting, dormancy, and abscission. The primary classes of plant hormones include auxins, gibberellins, cytokinins, abscisic acid, ethylene, jasmonates, brassinosteroids, and salicylates. Additionally, some secondary metabolites, such as nitric oxide (NO) and strigolactones, have been identified as having hormone-like functions in plant growth regulation.

The significance of plant hormones extends beyond mere growth regulation; they are integral to the plant's defense mechanisms against biotic and abiotic stresses. When plants face challenges such as pathogen attacks, herbivory, drought, or salinity, plant hormones initiate defense responses that can mitigate damage and enhance survival. This dual role of promoting growth while also facilitating stress responses underscores the importance of plant hormones in agriculture. By influencing crop yield and resilience, research into plant hormones has become vital for improving agricultural practices and ensuring food security.

Given the low concentrations of plant hormones—often in the range of 0.1 to 50 ng/g of fresh weight—accurate detection and quantification are challenging. The complexity of plant extracts, which contain a myriad of secondary metabolites, can interfere with the analysis of these hormones. Therefore, establishing effective extraction and purification methods is essential for isolating phytohormones from plant materials.

The extraction process typically begins with selecting fresh or lyophilized plant materials, which are then ground under liquid nitrogen to preserve their integrity. Various solvent extraction methods are employed to isolate plant hormones from these materials. However, because the crude extracts contain a high concentration of secondary metabolites, additional purification techniques are necessary. Methods such as liquid-phase extraction, solid-phase extraction, and solid-phase microextraction are commonly used to enrich the target hormones while minimizing background interference. This purification step is crucial for obtaining samples that are suitable for quantitative analysis.

Once the plant hormones have been extracted and purified, the next step involves their detection. Mass spectrometry (MS) is a powerful analytical technique that significantly enhances the selectivity and sensitivity of hormone detection. Tandem mass spectrometry (MS/MS), which can be performed using time-tandem ion trap mass spectrometry or spatially tandem triple quadrupole (QQQ) mass spectrometry, is particularly effective for quantifying phytohormones. The multiple reaction monitoring (MRM) mode is frequently employed in these analyses, allowing for the simultaneous detection of multiple hormones in a single sample.

Ultra-performance liquid chromatography (UPLC) is another advanced technique that, when combined with mass spectrometry, greatly improves the efficiency of hormone analysis. UPLC utilizes columns packed with small particle sizes (typically 1.7 μm), enabling high separation capacity and rapid analysis under high pressure (up to 1000 bar). This combination of UPLC and MS not only enhances the throughput of hormone detection but also allows for the precise quantification of a wide range of plant hormones, even in valuable and rare plant mutant materials.

In summary, plant hormones are vital organic compounds that regulate numerous physiological processes in plants, contributing to their growth, development, and stress responses. The accurate determination of these hormones is essential for advancing agricultural practices and improving crop yields. Through sophisticated extraction, purification, and detection methods, researchers can gain deeper insights into the roles of plant hormones, paving the way for innovative solutions to enhance plant health and productivity. As our understanding of these complex signaling molecules continues to evolve, the potential for harnessing their power in agriculture remains immense, promising a future of more resilient and productive crops.