High Aluminum Resistance in Buckwheat¹
I. Al-induced Specific Secretion of Oxalic Acid from Root Tips

Shao Jian Zheng², Jian Feng Ma^*, and Hideaki Matsumoto

Research Institute for Bioresources, Okayama University, Chuo 2-20-1, Kurashiki 710, Japan (S.J.Z., J.F.M., H.M.); and Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Tsukuba, Japan (S.J.Z., H.M.)

High Al resistance in buckwheat (Fagopyrum esculentum Moench. cv Jianxi) has been suggested to be associated with both internal and external detoxification mechanisms. In this study the characteristics of the external detoxification mechanism, Al-induced secretion of oxalic acid, were investigated. Eleven days of P depletion failed to induce secretion of oxalic acid. Exposure to 50 µM LaCl₃ also did not induce the secretion of oxalic acid, suggesting that this secretion is a specific response to Al stress. Secretion of oxalic acid was maintained for 8 h by a 3-h pulse treatment with 150 µM Al. A nondestructive method was developed to determine the site of the secretion along the root. Oxalic acid was found to be secreted in the region 0 to 10 mm from the root tip. Experiments using excised roots also showed that secretion was located on the root tip. Four kinds of anion-channel inhibitors showed different effects on Al-induced secretion of oxalic acid: 10 µM anthracene-9-carboxylic acid and 4,4-diisothiocyanatostilbene-2,2-disulfonate had no effect, niflumic acid stimulated the secretion 4-fold, and phenylglyoxal inhibited the secretion by 50%. Root elongation in buckwheat was not inhibited by 25 µM Al or 10 µM phenylglyoxal alone but was inhibited by 40% in the presence of Al and phenylglyoxal, confirming that secretion of oxalic acid is associated with Al resistance.

Plant Physiol. (1998) 117: 745-751
Copyright Clearance Center:   0032-0889/98/117/0745/07
© 1998 American Society of Plant Physiologists

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