Ferulic acid pretreatment alleviates heat stress in blueberry seedlings by inducing antioxidant enzymes, proline, and soluble sugars

Heat causes stress in blueberry; therefore, the present study aimed to investigate whether exogenous ferulic acid (FA) might protect plants against heat stress and to analyze possible mechanisms underlying such protection. Blueberry (Vaccinium corymbosum) seedlings were pretreated with 0.6 mM FA for 1 d and then kept at normal (25/20 A degrees C) or elevated (39/30 A degrees C) temperatures for 3 d. One day of FA pretreatment increased transcriptions of genes encoding iron superoxide dismutase, cytoplasmic copper/zinc superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase and elevated content of proline and soluble sugars in leaves. When the FA-pretreated blueberries were exposed to heat, transcriptions of these genes and content of proline and soluble sugars were higher than after heat treatment alone. Under heat, FA pretreatment also enhanced transcriptions of genes encoding chloroplast copper/zinc superoxide dismutase, catalase, glutathione peroxidase, monodehydroascorbate reductase, and dehydroascorbate reductase. This corresponds with increased activities of superoxide dismutase and glutathione peroxidase and is consistent with elevated content of ascorbate and glutathione in the FA-pretreated and heat-stressed blueberries. Compared with heat treatment alone, the combination of FA pretreatment and heat enhanced content of endogenous FA, decreased production of superoxide anion, and content of hydrogen peroxide and malondialdehyde, and also increased relative water content and osmotic potential in the leaves. Thus, pretreatment with FA mitigated the heat stress in the blueberries by elevating endogenous FA content, reducing accumulation of reactive oxygen species, and increasing proline and soluble sugar content.