Metabolomic analyses reveal substances that contribute to the increased freezing tolerance of alfalfa (Medicago sativa L.) after continuous water deficit

Abstract

Background: Alfalfa is a high-quality forage cultivated widely in northern China. Recently, the failure of alfalfa plants to survive the winter has caused substantial economic losses. Water management has attracted considerable attention as a method for the potential improvement of winter survival. The aim of this study was to determine whether and how changes in the water regime affect the freezing tolerance of alfalfa. Results: The alfalfa variety WL353LH was cultivated under water regimes of 80 and 25% of water-holding capacity, and all the plants were subjected to low temperatures at 4/0°C (light/dark) and then − 2/− 6°C (light/dark). The semi-lethal temperatures were lower for water-stressed than well-watered alfalfa. The pool sizes of total soluble sugars, total amino acids, and proline changed substantially under water-deficit and low-temperature conditions. Metabolomics analyses revealed 72 subclasses of differential metabolites, among which lipid and lipid-like molecules (e.g., fatty acids, unsaturated fatty acids, and glycerophospholipids) and amino acids, peptides, and analogues (e.g., proline betaine) were upregulated under water-deficit conditions. Some carbohydrates (e.g., Dmaltose and raffinose) and flavonoids were also upregulated at low temperatures. Finally, Kyoto Encyclopedia of Genes and Genomes analyses revealed 18 significantly enriched pathways involved in the biosynthesis and metabolism of carbohydrates, unsaturated fatty acids, amino acids, and glycerophospholipids. Conclusions: Water deficit significantly enhanced the alfalfa' freezing tolerance, and this was correlated with increased soluble sugar, amino acid, and lipid and lipid-like molecule contents. These substances are involved in osmotic regulation, cryoprotection, and the synthesis, fluidity, and stability of the cellular membrane. Our study provides a reference for improving alfalfa' winter survival through water management.

Plastic response of Medicago sativa L. root system traits and cold resistance to simulated rainfall events

“…Appropriate cultivation measures are also an effective way to improve cold resistance. Water plays an important role in the winter hardiness of alfalfa because freezing injury is mainly caused by cell dehydration (Xu et al, 2020a;2020b;Zhang et al, 2015). Water can not only affect the cold resistance of alfalfa by changing the morphology and spatial distribution of the root system, but also protect cells from low-temperature damage through physiological metabolic pathways (Castonguay et al, 2006).…”

“…According to the cross acclimation theory (Kong & Henry, 2019a;2019b), low-frequency heavy precipitation will increase the time plants spend in drought conditions, and so improve the cold resistance of alfalfa. This is because drought can enhance the antioxidant capacity and osmotic regulation of plants, including changes in malondialdehyde (MDA) (Schwab et al, 1996), proline (Pro) (Janska et al, 2010), soluble sugars (SS) (Trischuk et al, 2014) and starch content (Xu et al, 2020a), and these are closely related to the cold resistance of alfalfa. MDA reflects the degree of membrane lipid peroxidation in the cell membrane, and its content is directly proportional to the low temperature injury of alfalfa (Schwab et al, 1996).…”

“…Soluble sugar acts as osmotic regulator, cryoprotectant, and signaling molecule to stabilize the cell membrane and scavenge reactive oxygen species under low temperature (Trischuk et al, 2014). Starch can be broken down into soluble sugar to improve the cold resistance of alfalfa (Xu et al, 2020a).…”

Can omics deliver temperature resilient ready-to-grow crops?

“…Treatments resulted in increased soluble sugars, total amino acids, especially proline, and higher lipids content, including fatty acids, unsaturated fatty acids, and glycerophospholipids. The enhanced FS tolerance (at 0 to À6 C) is mainly contributed by improved metabolic pathways and some abundant flavonoids and carbohydrates [142]. Similarly, FS (À6.5 C) tolerance can be enhanced by using a strategy of exogenous application of enhanced antioxidant capacity and is reported in spinach (Spinacia oleracea L.) [143].…”

“…Recently, in alfalfa, FS tolerance has been improved by working on the water deficit treatment strategy [142]. Treatments resulted in increased soluble sugars, total amino acids, especially proline, and higher lipids content, including fatty acids, unsaturated fatty acids, and glycerophospholipids.…”