Physiological characteristics of rice cultivar oochikara and its short-root near isogenic line IL-srt1

The shoot and root characters, the bleeding rate and the photosynthetic rate in flag leaves of rice cultivar Oochikara were compared with its short-root near isogenic line IL-srt1 at the heading stage. The bleeding rate per plant in IL-srt1 was only 56% of that in Oochikara. The total root length and total root weight in IL-srt1 were 30% and 35% of those in Oochikara, respectively. On the other hand, the bleeding rate per total root length and that per total root weight in IL-srt1 were 188% and 163% of those in Oochikara, respectively, showing a significant difference between the two lines. Thus, although the root mass was larger in Oochikara than in IL-srt1, the bleeding rate per unit root mass was higher in IL-srt1 than in Oochikara. These results suggest that the physiological activities of total root in IL-srt1 were lower than that in Oochikara, due to the smaller root mass, and that IL-srt1 had higher physiological activities per unit root mass than Oochikara. There was no significant difference in photosynthetic rate between the two lines, suggesting that the short-root gene srt1 did not affect the photosynthesis.