RESPONSE MECHANISMS OF CABBAGE HEAD TO DIFFERENT STRENGTH LEVELS OF MECHANICAL IMPACT STRESS

Fresh fruits and vegetables are exposed to various stresses during harvesting and postharvest handling. The responses of fresh produce to mechanical stress such as wounds and mechanical injuries can lead to the onset of physiological disorders and quality deterioration. We previously found that mechanical impact stress affected changes in respiration rate, ethylene production, and compositional properties of fresh produce. Impact stress also induces a wide range of responses through gene expression relating signal transduction and cellular metabolism. In this study, we investigated the effect of different strength levels of mechanical impact stress (dropping treatment; 0, 5, 10, 20, or 40 cm height) on stress-responsive gene expression which is implied to influence the cellular metabolisms and storage quality of postharvest cabbage head. Dropping treatment enhanced the expression of calmodulin (CaM)-encoding gene (BoCam1), phospholipase D (PLD)-encoding genes (BoPLD1 and BoPLD2), and ascorbate peroxidase (APX)-encoding gene (BoAPX2), lipoxygenase (LOX)-encoding gene (BoLOX), and S-adenosyl-methionine (SAMS) encoding gene (BoSAMS). However, the highest expression level of each gene was observed differently depending on the impact strength level and time period after dropping application. From overall results, the rapid stress response behavior of BoCam1 (0.5 h) and BoAPX2 (1 h) indicated their action at the early stage of stress response metabolism, which are reported to be homologue to the model plants. Delayed response of BoPLD1 (3 h), BoPLD2 (3 h), BoSAMS (3 h), and BoLOX (3 days) demonstrated the downstream cascade of stress responses, possibly affecting the changes in eating quality of cabbage.