Plant chemical priming by humic acids

Background Global market of humic substances has been increasing steadily based on the perception of the multifunctional properties as plant biostimulant, microbial vehicle and plant protective agent against environmental stress. Some field assays and many experimental observations have shown that humic matter could relieve the abiotic stress effects. Here, we explored the plant chemical priming effect concept, i.e., plant preconditioning by prior exposure to an appropriate dose of humic acids with the objective to reduce toxicity from a subsequent harmful exposure to abiotic stressor, such as salinity, drought, heavy metals and humic acids themselves. Materials and methods The prime state (PS) was characterized using traditional stress markers like proline content and catalase activity was well as the transcription level of mRNA of phytohormones-responsive genes, cell signaling, stress-responsive genes and transcription factors. A dose-response curve was built for stressor agents since maize seedlings in the PS were submitted to salinity, drought, chromium toxicity and humic acids concentration to reduce 50% of root fresh weight with respect to control plants. Results The PS or adaptive response by biostimulation of humic substances was described at transcriptional level, where the hormonal signaling pathways including abscisic acid, gibberellic and auxins, specific abiotic functional and regulatory stress-responsive genes were positively modulated. The negative impact of stressor agents was alleviated in the maize seedlings primed by humic acids. Conclusion Chemical priming by humic substances is a promising field tool in plant stress physiology and crop stress management.