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 th e deposition of (1,3)-beta-glucans (callose) as a marker for injury. T wo-day-old seedlings were grown for forty hours in nutrient solutions with or without added Al, and callose deposition was quantified by spe ctrofluorometry (0-1000 mu M Al) and localized by fluorescence microsc opy (0 and 400 mu M Al). Results suggested that Al caused little damag e to leaves. No callose was observed in leaves with up to 400 mu M Al treatment. In contrast, root callose concentration increased with Al t reatment, especially in the Al-sensitive lines. At 400 mu M Al, root c allose concentration of Al-sensitive Scout 66 was nearly four-fold tha t of Al-resistant Atlas 66. After Al treatment, large callose deposits were observed in the root cap, epidermis and outer cortex of root tip s 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 callos e-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 wi th stress perception.