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Abstract
Aluminum (Al) effects on fatty acid composition and on the lipid peroxidation of a purified plasma membrane fraction of root apices of two sorghum cultivars were studied. Palmitic and linoleic acids were the major fatty acids in the root apices of sorghum, independent of the Al presence in nutrient solution. After Al treatment, the C18:0/C18:3 and C18:2/C18:3 ratios increased, while the C18:2/C16:0 ratio remained unchanged in the Al-sensitive cultivar but all three ratios decreased in the Al-tolerant cultivar. The double bond index and unsaturated fatty acid/saturated fatty acid ratio decreased in both cultivars but with higher intensity in the Al-sensitive cultivar. The linolenic and palmitic acids were probably the most important fatty acids associated with Al tolerance in the two sorghum cultivar studied. In the presence of Al, these two fatty acids decreased in the Al-sensitive cultivar but increased in the Al-tolerant cultivar. Plasma membranes obtained from the entire root system of the Al-sensitive cultivar showed higher concentration of malonaldehyde-thiobarbituric acid complex than the Al-tolerant cultivar, independent of the Al treatment. In root apices, in the absence of Al, there was no difference between cultivars. In the presence of Al, however, the concentration of the malonaldehyde-thiobarbituric acid complex increased about 43% but only in the Al-sensitive cultivar. So, under Al treatment, the Al-sensitive cultivar produced 36% more malonaldehyde-thiobarbituric acid complex than the Al-tolerant cultivar, which was taken as indicative of higher reactive oxygen species production and higher fatty acid peroxidation of the plasma membrane of this cultivar.
ACKNOWLEDGMENTS
The authors acknowledge the Brazilian National Research Council (CNPq)for financial support and fellowships. We are also indebted to Dr. James Jackson Griffith for helpful hints in English usage.
