Effect of temperature on the gross morphology of leaves in Chinese cabbage (Brassica campestris L.)

Morphological changes in leaves were investigated to clarify the effect of temperature on head formation in chinese cabbage. 1) Seedlings of Chinese cabbage (cv. Nozaki-Kohai No. 3) were grown in a phytotron at day/night temperatures of 30/25 (high), 23/18 (medium), and 15/10 (low) °C. 2) Leaves showed the most rapid growth at the high temperature, while the rate of leaf production was highest at the medium temperature. Thus, the plants were larger at higher temperatures soon after the start of the temperature treatment, but after 5-6 weeks the plants were largest at the medium temperature. 3) The position on the stem of the first one of the folded leaves, which make the “small head” (embryonic head), varied with temperature conditions; the lower the temperature, the lower the position of the first folded leaf. 4) The leaf shape of Chinese cabbage is determined by the relationship between lamina width and midrib length. Lamina width was largest at the medium temperature, while midrib length was larger at higher temperatures. Consequently, the ratio of the midrib length to the leaf width (lamina width) decreased proportionately with the decrease in temperature. In Chinese cabbage, as opposed to cabbage and lettuce, the midrib of the leaf does not reach the leaf apex as the “midrib”. It is thought that the ratio of the midrib length to the leaf width is more suitable than the length-width ratio of the leaf in considering the effect of temperature on the leaf shape of Chinese cabbage. 5) From the leaf shape and the position in which the first folded leaf was observed, it is thought that the head formation physiologically starts earliest under lower temperature conditions.