Effects of low temperature on the sugar and ascorbic acid contents of Komatsuna (Brassica campestris L.) under limited solar radiation

Abstract

The effects of low temperature on the sugar and ascorbic acid contents of Komatsuna (Brassica campestris L.) plants grown under limited solar radiation in the greenhouse were evaluated. Komatsuna plants were grown in a greenhouse in which the mean air temperature was maintained between 13 °C and 15 °C (defined as the 'cool temperature' condition). The solar radiation in the greenhouse fluctuated between 2 and 4 MJ/m2 · day-1 during the experiment. When Komatsuna plants grew to about 20 cm height, they were transferred to a greenhouse in which the mean air temperature fluctuated between 2 °C and 3 °C (defined as the 'cold temperature' or 'cold treatment'). The total sugar contents in leaf blades and in petioles of Komatsuna plants increased rapidly as a function of the cold treatment. The total ascorbic acid content in the leaf blades increased rapidly after the initiation of cold treatment, whereas that content in the petioles increased gradually. On the other hand, the composition of the leaf blades and petioles in the Komatsuna plants did not change when grown continuously in the cool plot. The data show that cold treatment promoted the per unit area production of the total sugar and total ascorbic acid. These results indicate that cold treatment could improve the nutritional qualities of Komatsuna plants, even under limited solar radiation in winter.