Cold stress and freezing tolerance negatively affect the fitness of Arabidopsis thaliana accessions under field and controlled conditions

Main conclusion Higher acclimated freezing tolerance improved winter survival, but reduced reproductive fitness of Arabidopsis thaliana accessions under field and controlled conditions. Abstract Low temperature is one of the most important abiotic factors influencing plant fitness and geographical distribution. In addition, cold stress is known to influence crop yield and is therefore of great economic importance. Increased freezing tolerance can be acquired by the process of cold acclimation, but this may be associated with a fitness cost. To assess the influence of cold stress on the fitness of plants, long-term field trials over 5 years were performed with six natural accessions of Arabidopsis thaliana ranging from very tolerant to very sensitive to freezing. Fitness parameters, as seed yield and 1000 seed mass, were measured and correlation analyses with temperature and freezing tolerance data performed. The results were compared with fitness parameters from controlled chamber experiments over 3 years with application of cold priming and triggering conditions. Winter survival and seed yield per plant were positively correlated with temperature in field experiments. In addition, winter survival and 1000 seed mass were correlated with the cold-acclimated freezing tolerance of the selected Arabidopsis accessions. The results provide strong evidence for a trade-off between higher freezing tolerance and reproductive fitness in A. thaliana, which might have ecological impacts in the context of global warming.

Salicylic Acid-Mediated Diacylglycerol/Triacylglycerol Conversion Affects the Freezing Tolerance of Arabidopsis

Diacylglycerol (DAG) is likely converted to triacylglycerol (TAG) by the enzyme diacylglycerol acyltransferase (DGAT), and this conversion is important in freezing tolerance of Arabidopsis. The phytohormone salicylic acid (SA) plays important roles in the chilling and freezing tolerance of plants. In our study, we analysed the chilling phenotype, proline and sugar accumulation, phytohormone measurement, and lipid profiling of dgat1 mutants during chilling or freezing stress. We found that dgat1-1 mutants exhibited higher sensitivity to long exposure to cold stress and showed lower proline and sugar accumulation under cold acclimation conditions. The freezing-sensitive phenotype of dgat1 mutants can be ameliorated by mutations of key salicylic acid (SA) signalling components SAG101, EDS1, and PAD4 through phenotyping analysis of double mutants. Dgat1 mutants accumulated more SA, ABA, JA-Ile (jasmonate isoleucine) and OPDA (12- oxyphytodienoic acid) during freezing stress and after recovery. In addition, the DAG/TAG content in the SA-deficient mutant sid2 was lower than that in the wild type, while the SA-excessive accumulated mutant siz1 showed the opposite trend. In summary, SA could mediate the freezing tolerance of Arabidopsis by regulating the ratio of DAG and TAG, which influences the integrity of the membrane.

Exogenous Glycine Betaine Application Improves Freezing Tolerance of Cabbage (Brassica oleracea L.) Leaves

Exogenous glycine betaine (GB) application has been reported to improve plant tolerance to various abiotic stresses, but its effect on freezing tolerance has not been well studied. We investigated the effect of exogenous GB on freezing tolerance of cabbage (Brassica oleracea L.) leaves. Seedlings fed with 30 mM GB via sub-irrigation showed effectively assimilated GB as evident by higher GB concentration. Exogenous GB did not retard leaf-growth (fresh weight, dry weight, and leaf area) rather slightly promoted it. Temperature controlled freeze-thaw tests proved GB-fed plants were more freeze-tolerant as indicated by lower electrolyte leakage (i.e., indication of less membrane damage) and alleviating oxidative stress (less accumulation of O2•− and H2O2, as well as of malondialdehyde (MDA)) following a relatively moderate or severe freeze-thaw stress, i.e., −2.5 and −3.5 °C. Improved freezing tolerance induced by exogenous GB application may be associated with accumulation of compatible solute (proline) and antioxidant (glutathione). GB-fed leaves also had higher activity of antioxidant enzymes, catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD). These changes, together, may improve freezing tolerance through membrane protection from freeze-desiccation and alleviation of freeze-induced oxidative stress.