| Abstract: | Abstract Triticale (X Triticosecale Wittmack), a hybrid of wheat and rye, shows a high degree of aluminum (Al) tolerance, but variation in Al resistance between cultivars does exist. The mechanisms responsible for differential Al resistance in 10 triticale cultivars were investigated in this study. Triticale roots secreted both malate and citrate in response to Al stress. The amount of organic acid anions secreted was correlated positively to the relative root elongation (an index for Al resistance) and negatively to the Al content in root apices under Al stress, suggesting that the secretion of malate and citrate seems to be involved in the exclusion of Al from root tip. The Al‐induced secretion of malate and citrate was characterized using an Al‐resistant cultivar (ZC 237) and an Al‐sensitive cultivar (OH 1621). Root elongation was significantly inhibited in both ZC 237 and OH 1621 after 24 h of exposure to 30, 50, or 100 µM Al but was more strongly in OH 1621 than in ZC 237 at all Al concentrations tested. A marked lag phase (3 h) between the addition of Al and the secretion of organic acid anions was observed in both triticale cultivars, and the secretion increased with increasing external Al concentration. The two anion‐channel inhibitors, phenylglyoxal and niflumic acid, significantly inhibited the secretion of malate and citrate in ZC 237, with the degree of the inhibition of niflumic acid greater than that of phenylglyoxal. The Al‐induced secretion of malate and citrate decreased to a very low level at low temperature (4°C) in both cultivars. These results indicate that Al‐induced malate and citrate secretion from roots play important roles in excluding Al and thereby detoxifying Al in triticale. The Al‐induced organic acid anions were inhibited by anion‐channel inhibitors and were dependent on temperature. |
