CHARACTERIZATION OF 1,3-BETA-D-GLUCAN (CALLOSE) SYNTHESIS IN ROOTS OFTRITICUM-AESTIVUM IN RESPONSE TO ALUMINUM TOXICITY

To develop a sensitive marker for aluminum (Al) toxicity, synthesis of 1,3-beta-D-glucan (callose) in 5-mm root tips of Triticum aestivum wa s examined using spectrofluorometry. In a time course study where an A l-sensitive cultivar, Neepawa, was exposed to 75 mu M Al, a rapid phas e of callose synthesis was observed in the first 6-12 h, followed by a slower linear phase with no saturation up to 48 h. Treatment with Al increased accumulation of callose by 86% within 30 min and by 3821% af ter 48 h. In experiments comparing genotypes, more callose accumulated in roots of Al-sensitive cultivars than in Al-resistant cultivars/lin es after 2-h and 24-h exposure. Accumulation of callose increased at c oncentrations as low as 5 mu M Al and continued to increase with satur ation occurring between 250 and 500 mu M Al. callose synthesis was neg atively correlated with root growth. An Al-resistant experimental line , PT 741, and an Al-sensitive cultivar, Neepawa, accumulated callose t o a similar extent when faced with concentrations of Al that produced equal reductions in root growth. Because accumulation of callose refle cts cumulative exposure to Al, a second technique based upon labeling of callose with [C-14]glucose was developed to measure current synthes is. Treatment with Al increased incorporation of C-14 into laminarinas e (a 1,3(1,3; 1,4)-beta-D-glucan 3 (4)-glucanohydrolase, EC 3.2.1.6) d igestion products from cell-wall material isolated from both the Al-se nsitive Neepawa and Al-resistant PT 741. Greater incorporation of C-14 was observed in Neepawa over a broad range of Al concentrations (0-25 0 mu M). Results of both spectrofluorometric and C-14 labeling studies support the use of callose synthesis as a rapid and sensitive marker for Al-induced injury.