Effects of the amount and activity of roots on the cool-weather resistance in rice plants

Previously, we reported that the amount or activity of the root relative to shoot was an important factor relating to the sterility caused by cool temperatures. To elucidate the causal relationship between the relative amount or activity of roots and the cool-weather resistance, we modified the amount or activity of roots experimentally. When about 75% of roots or all tillers were cut off at the pollen mother cell formation stage just before the young microspore stage, there was no reduction in the fertility of the plants cooled at the young microspore stage. However, the fertility of the cooled plants was significantly reduced by the root cutting at the primary rachis branch differentiation stage, and also by the treatment of roots with a respiratory inhibitor or addition of glucose to the pots, which was expected to reduce the root activity through a reduction of soil. These results indicated that there was a causal relationship between the amount or activity of roots and the cool-weather resistance. In addition, the cool-weather resistance was reduced by the root cutting at the primary rachis branch differentiation stage bur not by similar treatment given just before the critical (cool-weather sensitive) stage. These facts suggest that the root does not affect the cool-weather resistance at the critical stage, but affects it at a stage earlier than the critical stage, for example, through the effect on the process of pollen formation.