Abstract
Red light irradiation at the beginning of dark period (RB) or blue light irradiation at the end of dark period (BE) at a low level promoted the biomass production in spinach (Hanyu and Shoji, 2000). We supposed this promotion of growth was related to the leaf area enlargement, and investigated how RB or BE affects leaf expansion. We grew spinach plants under white light at 220 µmol m-2 s-1 for 12 h with RB or BE at 30 µmol m-2 s-1 for 0.5 h. RB or BE promoted the biomass production accompanied by the increase in leaf area. Microscopic analysis of the leaf transverse sections revealed that RB increased the leaf cell size, while BE did not affected it. These results suggested that RB accelerated leaf expansion by the increase in leaf cell size and BE accelerated leaf expansion in the increase of leaf cell number.
