Abscisic acid, carbohydrate, and Glucosinolate metabolite profiles in Kimchi cabbage treated with extremely high temperatures and chitosan foliar application

Chitosan can help enhance disease resistance in plants by thickening leaves and alleviating environmental stresses, such as excess light intensity and extremely high temperature by promoting physiological activity. This study evaluated the effects of chitosan foliar application on Kimchi cabbage under high temperature stress. Six treatments were conducted, combining three photo-/dark periods temperature levels (20/16 °C optimal; 28/24 °C moderately high; and 36/32 °C extremely high) with and without chitosan foliar application (0 and 200 mg∙ L   −   1 ). Chitosan foliar application treatment sprayed once at 42 days after transplanting, and then temperature treatment immediately after chitosan foliar application conducted for up to eight days. At eight days after treatment (DAT), the leaf contents of abscisic acid (ABA) metabolites, i.e., phaseic acid (PA), dihydrophaseic acid (DPA), and ABA glucose ester (ABA-GE), were higher with chitosan foliar application than without chitosan treatments under moderately high and extremely high temperature conditions. PA and DPA were present at higher levels than the other metabolites. At eight DAT, the glucose and fructose contents in Kimchi cabbage treated with chitosan foliar application were higher than in those without chitosan foliar application when plants were under the moderately high and extremely high temperature conditions. Glucosinolate metabolite (gluconapin, glucobrassicanapin, glucobrassicin, and 4-methoxyglucobrassicin) content was higher with chitosan foliar application than without chitosan foliar application under the extremely high temperature treatment. When exposed to extremely high temperature, chitosan foliar application mitigated the damage caused to Kimchi cabbage by high temperature stress. Overall, chitosan foliar application can alleviate the high temperature stress that can occur during the spring cultivation season in Kimchi cabbage, and the application of chitosan is therefore a feasible strategy for stabilizing production of Kimchi cabbage.