2017 ASHS Annual Conference

Antioxidant phenolic compounds, rich in vegetables, contribute to maintain and promote human health. The application of temporary abiotic stresses before vegetable harvest has been a potential cultural strategy to enhance the phytochemicals in greenhouses or plant factories. This study aimed to determine the effect of combined treatment of low temperature and UV-A light on the accumulation of phenolic compounds in kale (Brassica oleracea var. acephala ‘Manchoo Collard’). Fourteen-day-old kale seedlings were cultivated in a growth chamber (air temperature of 20℃, relative humidity of 60%, PPFD of 128 µmol·m^-2·s^-1) for 3 weeks. After then, kale plants were subjected to combined stress (10℃ plus UV-A LED irradiation of 30.3 W/m²) for 3 days and compare with those under single stress treatment (4℃ or 10℃ or UV-A LED irradiation). All the plants were recovered for 2 days under normal growing conditions right. The combined treatment did not have a negative effect on growth characteristics such as fresh and dry weights of shoots and roots, leaf area, leaf number and SPAD value and UV-A treatment significantly increased compared to the control. The specific leaf weight was the highest in the plants subjected to the combined stress. The result of photosynthetic rate was similar patterns with those of growth characteristics at 3 days of treatment. Fv/Fm of both UV-A treatment and the combined treatment started to decrease at 3 hours and increased again at 3.5 days of treatment. Total phenolic contents of the combined treatment at 2 and 3 days of treatment and 1 day of recovery were 1.4-, 1.6- and 1.5-fold higher than those of the control, respectively. The activity of phenylalanine ammonia-lyase was approximately 1.3-fold higher in the combined treatment compared to the control at 1 day of treatment. The combined treatment had significantly higher value in the most of measurement parameters than the other single treatments during whole sampling period. These findings suggested that the combination of properly low temperature and UV-A irradiation was effective to improve phenolic content of leafy vegetables such as kale before harvest.