Role of Osmotic Regulation and Cryoprotectant Substances in the Freezing Tolerance of Alfalfa in Cold, Dry Conditions

Abstract

Background: Freezing temperatures are a limiting factor hindering the survival of alfalfa (Medicago sativa L.) through winter. Soil drought also damages alfalfa crowns and can affect their regeneration. Therefore, it is important to determine the effects of cold, dry conditions on alfalfa to develop effective water management strategies in winter. Methods: Cold, dry conditions were established in the laboratory and the freezing tolerance of crowns was compared between the alfalfa cultivars ‘WL440HQ’ and ‘ZhaoDong’. The degree of freezing tolerance was estimated on the basis of relative electrolyte leakage and semi-lethal temperature. The effects of cold, dry conditions on alfalfa crowns were determined by investigating the rate of water loss and the concentrations of soluble sugars (which function as cryoprotectants) and betaine and proline (which function as osmoregulation substances). Result: Compared with crowns of ‘ZhaoDong’, those of ‘WL440HQ’ showed a higher water loss rate in cold, dry conditions and were irreversibly damaged and their freezing tolerance was severely affected. In comparison, crowns from ‘ZhaoDong’ showed a lower water loss rate and lower relative electrolyte leakage under cold, dry conditions and their freezing tolerance was not significantly affected. The higher water loss rate and lower freezing tolerance were the direct causes of death of ‘WL440HQ’, the cultivar with a higher fall dormancy score. In cold, dry conditions, the content of proline, an osmotic regulation substance, increased in response to soil water deficit and may have improved the ability to withstand freezing temperatures by preventing rapid water loss. In addition, sucrose, fructose, galactose and stachyose contents in the crown increased under cold, dry conditions and may have enhanced freezing tolerance because of their function as cryoprotectants. The results of this study indicate that maintaining soil moisture within the range suitable for the growth of crowns is important for the successful overwintering of alfalfa.

How Antioxidants, Osmoregulation, Genes and Metabolites Regulate the Late Seeding Tolerance of Rapeseeds (Brassica napus L.) during Wintering

“…Research has shown that high-chilling-tolerance cultivars accumulated more antioxidants, enzymes and osmoregulation substances in the anti-stress and environment adaption process compared with low-chilling-tolerance cultivars [41,42]. In more detail, the functions of the soluble protein and carbohydrate levels on the improvement in freezing tolerance were validated in sauvignon [43], while the functions of increased proline and carbohydrates under cold stress were also verified in alfalfa [44]. Furthermore, the enhanced chilling tolerance in watermelon achieved via suboptimal temperature acclimation was contributed to by improved photosynthetic adaptability and osmoregulation ability from substances such as proline, soluble sugar and sucrose [45].…”

Reduction of Drought Stress Effects on Guar (Cyamopsis tetragonoloba L.) using Ascorbic Acid and Calcium Carbonate

“…In these two drought treatments, foliar application with AA decreased the proline content more than that of Ca application. Generally, proline content increases in plants parallel to the rise of damage to cell membranes and the plant tries to mitigate the damage to membranes by increasing the proline level in its tissues (Shinde et al, 2016;Xu et al, 2022).…”

MdNAC104 positively regulates apple cold tolerance via CBF‐dependent and CBF‐independent pathways

“…Cold stress damages cell membrane structure, leading to decreased extracellular water potential, increased ion leakage and malondialdehyde (MDA) content, as well as overproduction of reactive oxygen species (ROS) (Ding et al ., 2019; Qi et al ., 2018). Plants have evolved various physiological mechanisms to alleviate damage caused by cold stress, which promote the accumulation of osmoregulatory substances and improve the activity of antioxidant enzymes (Hoermiller et al ., 2022; Wang et al ., 2020; Xu et al ., 2022b). The accumulation of dehydrins and osmotic regulating substances, such as soluble sugars, soluble proteins, betaine and proline, helps to reduce osmotic pressure and stabilize cell membranes, thus improving plant tolerance to cold stress (Feng et al ., 2013; Hayashi et al ., 1997; Hoermiller et al ., 2022; Meena et al ., 2019; Xin and Browse, 2010).…”