Studies on the mechanism of aluminum tolerance in pea (Pisum sativum L.) using aluminum-tolerant cultivar ‘Alaska’ and aluminum-sensitive cultivar ‘Hyogo’

The mechanism of aluminum (Al) tolerance was investigated in an Al-tolerant cultivar (Alaska) and an Alsensitive cultivar (yo o) of pea (Pisum sativum L.) seedlings. Al sen sitivity was evaluated as the degree of root elongation inhibition in a calcium solution. Fifty percent inhibition of the elongation was observed after 24h treatment with 5 µM Al in Alaska and with less than 2.5 µM Al in Hyogo. At 10 µM Al, both cultivars exhibited more than 70% inhibition, At 2.5 µM and 5 µM, Al triggered citrate secretion in both cultivars to the same extent, and the levels of Al accumulation in root apices were similar in both celti vare, indicating that the difference in Al tolerance observed in these cultivars was not re lated to the exclusion of Al with organic acid. Al treatment enhanced the production of reactive oxygen species (ROS) specifically in the elongation zone in both cultivars. Al dose and time course experiments indicated the existence of a strong positive correlation be tweera the root elongation inhibition and ROS production in both cultivars. At 10 pµM, Al inhibited the respiration rate in the root apex by 20% in Alaska and 30% in Hyogo but not significantly at lower concentrations. In the absence of Al, the ATP content in the root apex was 2 times higher in Alaska than in Hyogo. With the increase in Al concentration, the AT content in Alaska decreased and reached the same level in Hyogo at 5 µM Al, while the AT content in Hyogo did not change. These findings suggest that Al-triggered ROS production is a key factor for the root elongation inhibition in both cultivars, and the possible involvement of high ATP content in Alaska in the protection mechanism against ROS production and root elongation inhibition under Al stress.