This study aimed to determine the effects of foliar application of glutamic acid to alleviate the physiological damage caused by low air temperatures at early growth stages in Kimchi cabbages. Twenty-eight days after transplanting the Kimchi cabbage was exposed to a low (10 degrees C) air temperature for seven days and then treated with three different foliar sprays including pure water (control), 0.3% urea, and 10 mu mol.mol(-1) glutamic acid solutions (GA). After foliar treatments, cabbage plants were grown in non-shaded or 30%-shaded conditions. The maximum fresh weight of Kimchi cabbage was 1,700 g/plant when treated with glutamic acid, and the minimum fresh weight was 1,193 g/plant when treated with urea. Both head weight and yield were the greatest with glutamic acid treatment, which produced 4,845 kg/10a, while urea treatment produced only 3,400 kg/10a. The net photosynthetic rate and stomatal conductance were greatest under both glutamic acid and urea treatments compared to pure water. Low air temperature treatment of Kimchi cabbages adversely affected the net photosynthetic rate and stomatal conductance; however, an increase in the carboxylation rate and photosynthetic electron transport system efficiency was also observed. GA treatment reduced enzymatic activity in cold conditions compared to control plants that weren't treated. Notably, the H2O2 level was the lowest after glutamic acid treatment. These results indicated that foliar application of glutamic acid reduced physiological damage and enhanced antioxidant enzymes activity in Kimchi cabbages, which improved their tolerance to low air temperature.
