Differential response of plasma membrane versus chloroplast functions to freeze–thaw stress by Antarctic species, Deschampsia antarctica and Colobanthus quitensis, as explored through freeze-injury and post-thaw recovery

Antarctic plants employ distinct cold acclimation strategies: Deschampsia antarctica uses general membrane-chloroplast stabilization while Colobanthus quitensis relies on chloroplast-focused tolerance mechanisms. The two native vascular plants of Antarctica, Deschampsia antarctica and Colobanthus quitensis, persist in one of the most extreme terrestrial environments on Earth, where episodic freeze-thaw cycles are frequent even during the growing season. Survival under such conditions necessitates not only tolerance to freezing alone but also effective recovery from freeze-induced injuries-a composite trait referred to as freeze-thaw stress tolerance (FTST). Yet, estimates of FTST of Antarctic plants have remained inconsistent across studies, largely due to methodological differences in freezing regimes and injury assessment metrics. Here, we employed a standardized, ice-nucleation-controlled freeze-thaw protocol and assessed FTST using two independent physiological indicators: electrolyte leakage (membrane integrity) and chlorophyll fluorescence (Fv/Fm; PSII function). We further validated the LT₅₀ values-the temperature causing 50% injury-through post-thaw recovery (PTR) assays, and examined total soluble sugar dynamics as a metabolic indicator of recovery capacity. D. antarctica exhibited coordinated enhancements in both membrane and chloroplast resilience following cold acclimation, with LT₅₀ values from both metrics closely aligned. In contrast, C. quitensis demonstrated a chloroplast-centered acclimation strategy, characterized by pronounced improvement in Fv/Fm-based LT₅₀, while electrolyte-leakage based estimates remained largely unchanged. PTR results and sugar profiling supported the biological relevance of Fv/Fm as a more reliable FTST marker in C. quitensis. Together, these findings reveal distinct, species-specific acclimation frameworks to freeze-thaw stress; a global stabilization strategy in D. antarctica and a chloroplast-focused tolerance mechanism in C. quitensis, underscoring divergent evolutionary pathways for polar plant survival.