Abstract
Variation of the specific rate of dark respiration (mgCO2 g dry wt. -1h-1 measured at 29°C, Rs) with the age of the tissues and organs of rice cv. Suweon 258 and Nona Bokra, grown in the favorable field condition was measured and causal factors for the variation of Rs were studied. The leaf Rs excised 2 hours after darkening was higher by approximately 50 per cent than that excised after 15 hours after darkening when Rs was measured at 15 hours after darkining. The Rs of panicle and sheath excised at 2 hours after darkening was slightly higher than the ones excised after 15 hours after darkening when measured in the same conditions. The Rs of excised young developing tissues of various organs showed remarkably higher rate just after darkining and decreased almost linearly with time and rhythmic variation of Rs was hardly observed. On the other hand, those of excised mature tissues were lower and clear rhythmic variation of Rs characterized with higher rate early in the morning and often called "morning rise" was observed. The variation of Rs of young tissues was related to the sugar content during the measurement in a hyperbolic manner and it was also linearly related with nitrogen content. These results indicate that the relation between nitrogen and sugar content and Rs of the young developing tissues can be fundamentally simulated by the modified Michaelis-Menten equation. However, the Rs of older tissues did not fit to the above equation.
