Abstract
Biuret, a common impurity in urea fertilizers, is toxic to plants, but
little is known about the physiological mechanisms underlying its
toxicity. Here, we analyzed biuret toxicity in rice (Oryza
sativa) plants. We carried out uptake experiments using
15N-labelled biuret and demonstrated that biuret could
reach sub millimolar concentrations in rice plants. We also demonstrated
that the hydrolysis of biuret in plant cells could confer biuret
tolerance to rice plants. This occurred because transgenic rice plants
that overexpressed an exogenous biuret hydrolase cloned from a
soil bacterium gained improved tolerance to biuret toxicity. Our results
indicate that biuret toxicity is not an indirect toxicity caused by the
presence of biuret outside the roots, and that biuret is not quickly
metabolized in wild-type rice plants. Additionally, it was suggested
that biuret was used as an additional nitrogen source in transgenic rice
plants, because biuret hydrolase-overexpressing rice plants
accumulated more biuret-derived N, as compared to wild-type rice.