2022 Volume 67 Pages 51-55
When seedlings of the japonica rice cultivar Nipponbare (NPB) and the indica rice cultivar Habiganj Aman II (HA II) were incubated in the dark, “upper roots” that emerged from the upper portion of the nodal region of the coleoptile grew obliquely upward, and “lower roots” that emerged from the lower portion of the nodal region grew obliquely downward. In light, the upper roots turned their growth direction below the horizontal regardless of the irradiation from above and below. The trait of the upper roots growing upward in darkness and downward in light may lead to growth of the roots near the surface in the soil, contributing to the formation of the root system of rice, which has a higher proportion of roots distributed in shallower layers than other crops. The growth direction of the upper roots in the dark changed obliquely downward by excision of the seminal root. This excision significantly promoted the elongation of crown roots in HAII, but not in NPB. This difference might reflect the difference in root system depth of these cultivars.
