Abstract
This study aims at investigating how temperature affects the growth of rice embryo developlng under three temperature conditrons (30-25°C, 25-20°C 20°C) As expected the increase in length and in cell number was delayed as the temperature fell. But the cell number at the start of exponential growth and that at the changing point of the rate of increase in cell number did not vary with the temperature. Also, the coef-ficient of allometry between the length and thickness changed at definite embryo lengths irrespective of the variation in temperature. The modification in embryo shape, esti-mated by the residual variance in the coefficient of allometry and by the coeficient of variation in the ratio of the thickness to length, was wide at the globLllar stage irrespective of the temperature conditions and inceased as the temperature foll. Treatment consisting of exposure to low temperature of 20°C was applied at various developmental stages when embryos were developing at 30-25°C. Embryo growth was delayed by about 12 hours immediately after such treatment. This delay was observed in every treatment until the embryo had almost reached maturity. Therefore, the pat-tern of embryo growth curve is considered to be stable. On the other hand, the shape of the embryo varied more widely than that of the control after exposure to a temperature of 20°C at the globular stage (especially in the late period). When such treatment was applied after the second leaf had differentiated, the variation in embryo shape was not wider than in the control. These results indicate that embryo shape is unstable at the globular stage and become stable after the embryo is differentiated morphologically.
