| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2002: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2001: ¥2,700,000 (Direct Cost: ¥2,700,000)
|
|---|
| Research Abstract |
Secretion of organic acid anions from roots has been identified as a mechanism of resistance to Al. However, the process leading to the secretion of organic acid anions is poorly understood. We investigated the mechanism regulating Al-induced secretion of organic acid anions.
1. In buckwheat roots, ABA was found to be involved in the Al-induced secretion of oxalate. Only ABA rather than other phytohormone induced the secretion of exalate. When ABA synthesis was inhibited by Floridon, the Al-induced secretion of exalate was decreased. Al caused rapid increase in free ABA concentration in the root apices.
2. The effect of Al on the metabolism of organic acids was investigated in two lines of triticale (xTriticosecale Wittmark) differing in Al-induced secretion of malate and citrate and in Al resistance. Levels of citrate (room apices and mature root segments) and malate (mature segments only) acids in roots increased during exposure to Al, but similar changes were observed in both triticale genotypes. The in vitro activities of four enzymes involved in malate and citrate metabolism (citrate synthase, phosphoenol-pyruvate carboxylase, malate dehydrogenase and NADP-isocitrate dehydrogenase) were similar for sensitive and resistant lines in both root apices and mature root segments.
3. In barley (Hordeum vulgare L.), citrate was secreted from the roots in response to Al stress. A positive correlation between citrate secretion and Al resistance ((root elongation with Al) (root elongation without Al)) and a negative correlation between citrate secretion and Al content of root apices, were obtained, suggesting that citrate secretion from the root apices plays an important role in excluding Al and thereby detoxifying Al. The Al-induced secretion of citrate was characterized by a rapid, temperature-dependent, and no dose-response secretion.
|
