Varietal differences in the growth of rice plants in response to aluminum and silicon

Effects of Al (0-100 mu M) and Si (0-2,000 mu M) supplied singly or in combination on root growth of different rice varieties were examined under hydroponic conditions. Al addition inhibited root elongation of rice plants, and the inhibition increased with increasing amount of Al in the culture solution. Among 22 indica varieties and among 8 japonica varieties tested, IAC3 and Nakateshin-senbon were relatively tolerant to Al, respectively, whereas IR45 and Norin1 were relatively sensitive to Al, respectively. Si exerted a beneficial effect at all levels of Si treatment on indica varieties, whereas Si supply resulted in a slight increase in the root dry weight of japonica varieties only at the highest level (2,000 mu M Si). The alleviation of Al inhibition of rice root growth by Si was observed in the combination of Al and Si treatments. Alleviation was more pronounced for all the Si treatments in indica varieties than in japonica varieties, and the alleviation was maximum with 2,000 mu M Si in IR45. The alleviation effect by Si was more pronounced in the Al-sensitive varieties than in the Al-tolerant. varieties. The application of Si resulted in an increase in the contents of Al and Si in plants, and there was no relationship between the Al content and Al inhibition in plants.