1. Plant Freezing Adaptation
Plants adapt to fluctuating environmental conditions, and low temperature is a major stress. At subzero temperatures, extracellular ice formation withdraws water from cells, causing dehydration, and ice growth can damage membrane structures. To avoid freezing injury, many plants sense temperature decline, suppress growth, and acquire freezing tolerance through cold acclimation.
When temperatures rise, plants reduce freezing tolerance and resume growth. This process, termed deacclimation, balances stress tolerance and growth under variable temperatures and should be viewed as a dynamic adaptive process rather than a simple on–off switch.
We examined carbohydrate dynamics during cold acclimation and deacclimation, focusing on soluble sugars and cell wall–related components. Soluble sugars and specific cell wall components increased during cold acclimation, whereas soluble sugars decreased during deacclimation while some cell wall components were retained. Re-acclimated plants exhibited higher freezing tolerance than during the initial acclimation, suggesting that acclimation and deacclimation are not merely reversible processes but an adaptive strategy that prepares plants for subsequent low-temperature stress.
Plants increase their freezing tolerance when exposed to low temperatures, but growth is concurrently suppressed
2. Polysaccharides in Adaptation
The accumulation of soluble sugars and changes in membrane composition during cold acclimation have been regarded as major factors mitigating dehydration damage. In contrast, we show that structural modifications of the cell wall also play a key role in freezing tolerance. Remodeling of cell wall polysaccharides, together with the turnover of storage polysaccharides such as starch and fructans, contributes to osmotic adjustment and structural stability, indicating that polysaccharides function as part of the defense against freezing and dehydration.
Furthermore, changes in polysaccharide composition during cold acclimation modify the mechanical properties of cells and tissues and are manifested as morphological changes. By integrating cell wall remodeling, polysaccharide metabolism, and morphology, we aim to clarify the mechanisms of plant adaptation to low-temperature environments.
Cold exposure causes a wrinkled leaf surface
in Komatsuna.
3. Plant Desiccation Tolerance
In terrestrial environments, drought stress can cause membrane damage and cell wall deformation, ultimately leading to cell death. However, resurrection plants possess the remarkable ability to maintain cellular structure during extreme dehydration and rapidly resume metabolic activity upon rehydration.
The accumulation of trehalose has been suggested as a key factor in protecting cellular components under desiccation. Yet, trehalose alone cannot fully explain this tolerance, and other mechanisms are likely involved. For instance, Selaginella tamariscina is capable of withstanding severe dehydration without structural damage, while its close relative S. moellendorffii, despite accumulating trehalose, lacks comparable tolerance. This discrepancy implies roles for differences in membrane composition, protective proteins, and other factors.
Our laboratory aims to uncover the mechanisms underlying desiccation tolerance in resurrection plants by comparing S. tamariscina and S. moellendorffii, with a particular focus on the cell wall’s role in stress resistance. By elucidating these mechanisms, we hope to contribute to a broader understanding of the evolutionary survival strategies employed by land plants.
S. tamariscina rapidly recovers upon rehydration, even after extreme desiccation.