ACCUMULATION OF AL IN ROOT MUCILAGE OF AN AL-RESISTANT AND AN AL-SENSITIVE CULTIVAR OF WHEAT

To estimate rates of Al accumulation within the symplasm, all apoplast ic pools of Al need to be eliminated or accounted for. We have develop ed a revised kinetic protocol that allows us to estimate the contribut ion of mucilage-bound Al to total, nonexchangeable Al, and to eliminat e the mucilage as an apoplastic pool of Al. By comparing the Al conten t of excised root tips (2 cm) of wheat ( Triticum aestivum L.) with an d without the removal of the mucilage (using a 10-min wash in 1 M NH4C l), we found that Al bound to the mucilage accounted for approximately 25 to 35% of Al remaining after desorption in citric acid. The kineti cs of Al uptake into mucilage were biphasic, with a rapid phase occurr ing in the first 30 min of uptake, followed by a linear phase occurrin g in the remainder of the experimental period (180 min). By adopting a step for removal of mucilage into our existing kinetic protocol, we h ave been able to isolate a linear phase of uptake with only a slight d eviation from linearity in the first 5 min. Although we cannot unambig uously identify this phase of uptake as uptake into the symplasm, we b elieve this new protocol provides us with the most accurate quantitati ve estimate of symplastic Al yet available.