Response of Alfalfa (Medicago sativa L.) to Abrupt Chilling as Reflected by Changes in Freezing Tolerance and Soluble Sugars

Hongyu Xu,Zongyong Tong,Xianglin Li,Feng He

doi:10.3390/agronomy10020255

Hongyu Xu, Zongyong Tong + Show 2 more

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https://doi.org/10.3390/agronomy10020255

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Abstract

Abrupt-chilling events threaten the survival of alfalfa plants, the ability to cope with such condition should be considered during cultivar selection in the production. To assess biochemical and molecular responses of alfalfa to abrupt chilling, the cultivars “WL440HQ” (WL) and “ZhaoDong” (ZD) were subjected to a five-phase experimental regime that included two abrupt-chilling events. The freezing tolerance of the crown was determined as the semi-lethal temperature (LT50) calculated from electrolyte leakage. Soluble sugar concentrations were quantified by ion chromatography. The mRNA transcript levels of four genes encoding enzymes (β-amylase, sucrose phosphate synthase, galactinol synthase, and stachyose synthase) involved in sugar metabolism and two cold-regulated genes (Cas15A and K3-dehydrin) were quantified using quantitative real-time PCR analysis. During the abrupt-chilling events, the LT50 decreased significantly in ZD but not in WL. The rapid response of ZD to abrupt chilling may have been due to the large increases in raffinose and stachyose concentrations, which were consistent with increased transcript levels of the galactinol synthase and stachyose synthase genes. Transcript levels of the cold-regulated genes Cas15A and K3-dehydrin were correlated with increased freezing tolerance under abrupt chilling. The results provide a reference for selection of appropriate cultivars to reduce the risk of crop damage in production areas where early autumn or late spring frosts are likely.

Highlights

Alfalfa (Medicago sativa L.) is widely cultivated over more than 4 million ha in China
The contents of cryoprotectant substances are much lower before cold acclimation or after deacclimation [7,8,9]; at such stages, alfalfa is likely to be killed by frost [1]
In phase 5, both WL and ZD recovered some of the freezing tolerance that was lost during deacclimation in phase 4

Summary

Introduction

Alfalfa (Medicago sativa L.) is widely cultivated over more than 4 million ha in China. Two types of cold stress cause damage, namely, extremely low temperatures and abrupt chilling, of which the latter is exemplified by early autumn and late spring frosts [1,2]. The ability of alfalfa to resist low temperatures in winter is closely associated with fall dormancy [3], cold acclimation, and cold hardening [4]. Tolerance of alfalfa to gradually lowering temperatures is improved by cold acclimation [5]. The contents of cryoprotectant substances are much lower before cold acclimation (in early autumn) or after deacclimation (in late spring) [7,8,9]; at such stages, alfalfa is likely to be killed by frost [1]. Cold-resistant cultivars generally show low fall dormancy [10]

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