Hormonal Balance in Relation to Expression of Selected Genes Connected with Hormone Biosynthesis and Signalling—The Effect of Deacclimation Process in Oilseed Rape

Global climate change is causing increasing fluctuations in winter temperatures, including episodes of warm conditions above 9 °C. Such events disrupt cold acclimation in plants and can induce deacclimation, reducing frost tolerance and altering, among other things, hormonal regulation. This study investigated hormonal and molecular changes associated with cold acclimation and deacclimation in oilseed rape (<i>Brassica napus</i> L.) cultivars Kuga and Thure. Plants were grown under different conditions: non-acclimated (17 °C for three weeks), cold-acclimated (4 °C for three weeks), and deacclimated (16/9 °C day/night for one week). Detailed hormone analysis included auxins, gibberellins, cytokinins, stress-related hormones, and the expression of hormone-related genes (<i>BnABF2</i>, <i>BnAOS</i>, <i>BnARF1</i>, <i>BnARR6</i>, <i>BnICS1</i>, <i>BnRGA</i>, and <i>BnWRKY57</i>). Hormone concentrations in leaves changed dynamically in response to deacclimation with increased amounts of growth-promoting hormones and decreased amounts of stress hormones. Additionally, alterations in gene expression during deacclimation, such as in <i>BnABF2</i> and <i>BnICS1</i>, may function as protective mechanisms to help maintain or regain frost tolerance during reacclimation when temperatures decline again after the warm period. These findings improve the understanding of hormonal and molecular responses involved in the deacclimation of oilseed rape.