Climate change-related deacclimation disrupts sugar allocation and transport in winter oilseed rape (Brassica napus L.)

Winter oilseed rape achieves frost tolerance through cold acclimation (CA). CA is a process usually naturally occurring in autumn and triggered by low but non-freezing temperatures. Among various metabolic adjustments, changes in sugar management are one of the more important ones. Due to climate changes, increasingly frequent temperature fluctuations and appearance of warm breaks in late autumn/winter may lead to deacclimation (DA). DA may lower the frost tolerance causing problems with winter survival of plants. Physiological/biochemical background of DA still requires explanation. The aim of these studies was to answer the question if and how deeply deacclimation (one week at 16 ℃/9 ℃ [d/n]) modifies sugar metabolism in leaves, root necks and roots of two cultivars of winter oilseed rape. The studies include analysis of the changes in the sugar content supported by analysis of activity of selected enzymes involved in sugar synthesis/degradation and analysis of expression of sugar transporters. Typical changes accompanying CA were observed, such as an increase in the content of glucose, fructose, sucrose and kestose, as well as an increase in the activity of sucrose synthase and sucrose phosphate synthase (SUS and SPS) enzymes in all tested plant tissues compared to the non-acclimated control. DA reversed all these changes. CA decreased, while DA increased again the relative expression of sugar transporters BnSUC1 and BnSWEET11 . The negative impact of warm breaks during the period of cold acclimation on sugar accumulation and transport is discussed in the light of resumption of plant growth and reduced frost tolerance induced by deacclimation. • Deacclimation reduces CA-induced glucose, fructose, sucrose and kestose. • Stachyose strongly accumulates during deacclimation in all tested tissues. • Deacclimation suppresses SUS/SPS activity, but reactivates BnSUC1 and BnSWEET11 . • BnSUC1 expression negatively correlates with post-frost regrowth. • The loss of frost tolerance is linked to transporter-driven carbon reallocation.