Mechanisms of Aluminum Tolerance in Phosphoenolpyruvate Carboxylase Transgenic Rice

ABSTRACT

Transgenic rice, in which C4-phosphoenolpyruvate carboxylase (PEPC) is overexpressed, was grown in hydroponic culture to evaluate its tolerance for high aluminum (Al) content in relation to organic acid synthesis and exudation into the rhizosphere. With regard to root growth in short-term experiments, PEPC-transgenic rice was more tolerant of Al than the wild type. At increased Al levels in the root medium, root tips of the transgenic rice accumulated less Al than those of the wild type. Aluminum-induced oxalate exudation from roots occurred at increased rates in the transgenic line. Overexpression of C4-PEPC drastically increased PEPC activity in leaves of the transgenic rice, causing higher organic acid concentrations in leaves and roots. The increased organic acid concentrations seemed to cause higher exudation rates of oxalate from roots, leading to a detoxification of Al in the root apoplast and rhizosphere.

Keywords:

• PEPC-transgenic rice
• organic acid exudation
• Al tolerance mechanism

ACKNOWLEDGMENTS

We thank Dr. M. T. Miyao (National Institute of Agrobiological Sciences, Japan) and Dr. M. Matsuoka (Nagoya University, Bioscience Center, Japan) for kindly providing transgenic rice lines. H. H. B. is grateful to The Gen Foundation, U. K., and the Govt. of Hokkaido Prefecture, Hokkaido, Japan, for scholarships during her study at Hokkaido University.