© 2006 Heron Publishing—Victoria, Canada
Citrate-release-mediated aluminum resistance is coupled to the inducible expression of mitochondrial citrate synthase gene
in Paraserianthes falcataria
Hiroki Osawa (1, 2) and Katsumi Kojima (3)
1. Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan / 2. Corresponding author (osawa@fr.a.u-tokyo.ac.jp) / 3. Asian Natural Environmental Science Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan / Received July 18, 2005; accepted August 17, 2005; published online February 1, 2006
Summary
Aluminum (Al) resistance in some leguminous plants is achieved by enhanced citrate release from roots. Enhancement requires
several hours for complete activation and is postulated to involve Al-responsive genes or components. We examined the mechanism
of Al-induced citrate release by studying the relationship between citrate release and expression of the mitochondrial citrate
synthase (mCS) gene in three leguminous trees. Root elongation in Leucaena leucocephala (Lam.) de Wit was arrested within 24 h by 30 µM Al, whereas root elongation in Paraserianthes falcataria (L.) Neilson and Acacia mangium Willd. was inhibited < 50% by a 48-h treatment with 100 µM Al in calcium chloride solution. Roots of P. falcataria and A. mangium maintained enhanced release and accumulation of citrate for at least 28 days in response to Al treatment. Aluminum increased
the accumulation of mCS transcripts in P. falcataria roots, but not in L. leucocephala roots, and thus up-regulation decreased following removal of Al. Lanthanum did not alter the expression level of mCS. Aluminum increased mCS activity concomitantly with enhanced mCS gene expression in P. falcataria, whereas it did not affect mCS activity in L. leucocephala. Aluminum content in root apices of P. falcataria was increased by cycloheximide, supporting the idea that de novo synthesis of proteins is a prerequisite for Al resistance.
Our findings suggest that Al-inducible expression of mCS coupled with enhanced citrate release mediates Al resistance in P. falcataria.
Keywords:
acid soil, aluminum ion stress, gene expression, leguminous tree, organic acids metabolism, root exudates.
