Resistance of Fritillaria imperialis to freezing stress through gene expression, osmotic adjustment and antioxidants

Shokoofeh Hajihashemi,Marian Brestic,Marco Landi,Milan Skalicky

doi:10.1038/s41598-020-63006-7

Abstract

Plant survival in response to freezing stress depends on the efficient activation of tolerance mechanisms. Fritillaria imperialis exposure to freezing stress enhanced signalling molecules Ca2+ and H2O2 along with overexpression of Ca2+ signalling proteins (Ca2+ dependent protein kinases, CPK), followed by upregulation of NHX1 (Na+/H+ antiporter), LEA (late embryogenesis abundant proteins) and P5CS (1-pyrroline-5-carboxylate synthetase). Overexpression of OsCNGC6 was responsible for high accumulation Ca2+, Na+ and K+. The NHX1 gene product transported Na+ to vacuoles and increased cytosolic K+ content to re-establish ionic homeostasis under stress conditions. The reduced water potential of leaves was due to high accumulation of osmolytes and ions. No changes were observed in relative water content of leaves, which might be correlated with overexpression of the LEA gene, which protects against dehydration. High accumulation of H2O2 under freezing stress was responsible for activation of antioxidant systems involving SOD, phenols, anthocyanins, catalase and ascorbate peroxidase. Photosynthesis, suppressed in freezing-stressed plants, returned to normal levels after termination of freezing stress. Taken together, our findings suggest that Fritillaria efficiently tolerated freezing stress through induction of signalling mechanisms and overexpression of cold stress-responsive genes, and prevention of cold-induced water stress, oxidative stress and photosynthetic damage.

Highlights

Plant survival in response to freezing stress depends on the efficient activation of tolerance mechanisms
The Ψw of leaves subjected to freezing showed a significant reduction of 104% at day 7 and 35% at day[14] after snowing (DAS), while no significant change occurred at 21 day14 after snowing (DAS), compared to controls (Fig. 3a)
Cold stress rapidly leads to an influx of Ca2+ through Ca2+channels, like cyclic nucleotide-gated ion channels (CNGCs), into the cytosol[8]

Summary

Introduction

Plant survival in response to freezing stress depends on the efficient activation of tolerance mechanisms. Our findings suggest that Fritillaria efficiently tolerated freezing stress through induction of signalling mechanisms and overexpression of cold stressresponsive genes, and prevention of cold-induced water stress, oxidative stress and photosynthetic damage. Calcium-dependent protein kinases (CPKs) sense alterations in cytosolic Ca2+ level, and crosstalk with downstream signalling molecules including hormones, mitogen-activated protein www.nature.com/scientificreports kinases (MPKs) and reactive oxygen species (ROS), results in acclimation to the cold[7,9]. Many metabolites are thought to function as osmolytes to regulate cellular water levels and reduce dehydration. This beneficial solute behaviour allows them to stabilize enzymes, membranes and other cellular components. The quantification of net photosynthesis (PN), intercellular CO2 concentration (Ci), and water use efficiency (WUE) provides additional information about the effects of stress on photosynthesis[17,18]

Methods

Results

Conclusion