Impact of N-hexanoyl-DL-homoserine lactone priming on hormonal homeostasis in winter wheat

Quorum-sensing signal molecules in gram-negative bacteria, especially acyl-homoserine lactones (AHLs), are increasingly recognised as mediators of plant-microbe interactions in the rhizosphere. While AHLs are known to regulate bacterial physiology, their role in influencing plant hormonal balance and development remains unclear. We investigated the effects of seed priming with DL-C₆-HSL on endogenous phytohormone levels in winter wheat grown in the field over two seasons (2019-2020 and 2020-2021). At the tillering stage, levels of indole-3-acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GA₃) increased in both roots and leaves, while cytokinins (CKs) accumulated mainly in roots, and salicylic acid (SA) decreased in both organs. During flowering, IAA reached its peak, GA₃ declined, and ABA decreased only in leaves, whereas CK levels dropped in roots. Priming impacted root CK pools, with leaves consistently accumulating trans-zeatin-O-glucoside (t-ZOG) and trans-zeatin riboside (t-ZR); in roots, these CKs rose only at higher AHL concentrations. At the milk-wax ripening stage, IAA and SA declined, ABA peaked, and GA₃ dropped to its lowest levels in both organs. CK accumulation was several times higher in leaves than in roots, with t-ZR, t-ZOG, and isopentenyladenine (iP) dominating in both tissues. These hormonal changes correlated with reduced root growth during flowering but increased leaf growth at ripening, suggesting an adaptive redistribution of resources. Our study is the first to demonstrate, through multi-season field experiments, that seed priming with DL-C₆-HSL causes specific, stage-dependent changes in wheat hormonal homeostasis. Unlike earlier laboratory studies, our research provides direct evidence that bacterial autoinducers can be utilised as practical agronomic tools for crop improvement.