Deacclimation-Driven Reprogramming of Water Transport and Osmotic Protection in Winter Oilseed Rape

Winter oilseed rape achieves frost tolerance through cold acclimation, which develops naturally in autumn in response to low but non-freezing temperatures. However, ongoing climate change has led to an increasing instability in winter temperatures, with more frequent warm breaks. Such temperature fluctuations can induce deacclimation, resulting in a partial or complete loss of frost tolerance and reduced winter survival. Water management is a critical determinant of plant survival under such conditions, yet its regulation during the acclimation–deacclimation transition remains incompletely understood. This study investigated tissue-specific changes in key components of water management in winter oilseed rape subjected to non-acclimated, cold-acclimated, and deacclimated conditions. Proline accumulation, abscisic acid content in plant tissue and cell sap, and the expression of aquaporin genes BnPIP2 and BnTIP1 were analyzed in leaves, root necks, and roots. Cold acclimation induced a strong accumulation of proline and ABA, accompanied by marked downregulation of aquaporin expression in all tested tissue. Deacclimation resulted in partial reverse of proline and ABA. Aquaporins expression demonstrated tissue-specific recovery, showing increases in all tissue compared to cold-acclimated plants. Our findings demonstrate that coordinated actions of integrated water transport, osmotic adjustment, and hormonal signaling in regulating water balance and frost tolerance during winter temperature fluctuations.