THE EFFECT OF ALUMINUM EXPOSURE ON ROOT RESPIRATION IN AN ALUMINUM-SENSITIVE AND AN ALUMINUM-TOLERANT CULTIVAR OF TRITICUM-AESTIVUM

The effects of aluminum (Al) exposure on intact root respiration of an Al-sensitive (Scout-66) and an Al-tolerant (Atlas-66) cultivar of Tri ticum aestivum were investigated. Exposure to a wide range of Al conce ntrations (0-900 mumol) for 4 days stimulated respiration along the en ergy-conserving cytochrome pathway in both cultivars and increased the ratio of maintenance respiration to growth respiration. The maximum r ate of Scout-66 root respiration occurred after exposure to 100-200 mu mol Al. Atlas-66 root respiration peaked after exposure to 300-400 mum ol Al. Similarly, calculations of theoretical adenosine 5'-triphosphat e (ATP) production indicated that maximum daily rate of ATP production also increased upon exposure to Al in both cultivars, with peak ATP p roduction occurring during peak respiration. Maximum root respiration rates in both cultivars were related to the Al concentration that inhi bited root growth. Temporal exposure to 200 mumol Al quickly stopped r oot growth and stimulated cytochrome pathway respiration in Scout-66 a fter 4 days. Atlas-66 root growth and respiration were unaffected by 2 00 mumol Al. These results suggest that Al exposure imposes a demand f or additional metabolic energy. A model describing Al effects on root respiration is presented.