ALUMINUM-INDUCED DEPOSITION OF (1,3)-BETA-GLUCANS (CALLOSE) IN TRITICUM-AESTIVUM L

Aluminum (Al)-induced damage to leaves and roots of two Al-resistant (cv. Atlas 66, experimental line PT741) and two Al-sensitive (cv. Scout 66, cv. Katepwa) lines of Triticum aestivum L. was estimated using the deposition of (1,3)-beta-glucans (callose) as a marker for injury. Two-day-old seedlings were grown for forty hours in nutrient solutions with or without added Al, and callose deposition was quantified by spectrofluorometry (0-1000 mu M Al) and localized by fluorescence microscopy (0 and 400 mu M Al). Results suggested that Al caused little damage to leaves. No callose was observed in leaves with up to 400 mu M Al treatment. In contrast, root callose concentration increased with Al treatment, especially in the Al-sensitive lines. At 400 mu M Al, root callose concentration of Al-sensitive Scout 66 was nearly four-fold that of Al-resistant Atlas 66. After Al treatment, large callose deposits were observed in the root cap, epidermis and outer cortex of root tips of Scout 66, but not Atlas 66. The identity of callose was confirmed by a reduced fluorescence in Al-treated roots: firstly, after adding an inhibitor of callose synthesis (2-deoxy-D-glucose) to the nutrient solution, and secondly, after incubating root sections with the callose-degrading enzyme beta-D-glucoside glucohydrolase [EC 3.2.1.21]. Root callose deposition may be a good marker for Al-induced injury due to its early detection by spectrofluorometry and its close association with stress perception.