Abstract
Freezing tolerance and physiological/biochemical changes were investigated for cabbage (Brassica oleracea L. ‘Myeong-Sung’) leaves treated with 0.5 mM salicylic acid (SA) by sub-irrigation. SA treatment did not interfere with leaf-growth (fresh/dry weight, and leaf-area), rather promoted growth (leaf-area) as compared to the control. Temperature-controlled, laboratory-based freeze-thaw assays revealed that SA-treated leaves were more freeze-tolerant than controls as evident by less ion-leakage as well as malondialdehyde content after freeze-thaw stress treatments (−2.5 and −3.5 °C). SA treatment also significantly alleviated freeze-induced oxidative stress as evidenced by the lower accumulation of O2•− and H2O2, concomitant with higher activities of antioxidant enzymes (ascorbate peroxidase and superoxide dismutase) relative to the control. Specifically, SA-treated leaves had a greater abundance of compatible solute (proline) and secondary metabolites (phenolic/flavonoid contents). These changes, together, may improve freezing tolerance through protecting membranes against freeze-desiccation and mitigating freeze-induced oxidative stress.
Highlights
Freeze-thaw is one of the major abiotic stresses adversely affecting plant performance and yield
Despite the mean global temperature rising annually, the occurrence of erratic frost episodes during spring/fall has been increasing in recent years; these episodes are predicted to keep increasing in frequency in the future which can result in severe frost damage to this economically important horticultural crops [1,2,3,4]
The present study showed that the more freeze-tolerant Salicylic acid (SA)-treated leaves had higher proline content than control (Figure 5A), indicating that exogenous SA increases proline content, thereby improving freezing tolerance (FT)
Summary
Freeze-thaw is one of the major abiotic stresses adversely affecting plant performance and yield. Despite the mean global temperature rising annually, the occurrence of erratic frost episodes during spring/fall has been increasing in recent years; these episodes are predicted to keep increasing in frequency in the future which can result in severe frost damage to this economically important horticultural crops [1,2,3,4]. We are motivated to develop, at least transiently, an intervention strategy to improve the plants’ freezing tolerance (FT) which bears remarkable importance to providing sustainable agriculture. Exogenous application of various chemical compounds before a predicted freezing temperature has received substantial attention as a potential course of action for improving plant FT [5].
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