3.5 Biuret uptake in transgenic rice plants
The increment in plant heights of biuret-treated transgenic lines suggested that biuret was utilized as an additional N source. Therefore, we also determined biuret uptake in biuret hydrolase -overexpressing lines. The concentration of biuret-derived N was 2.6 and 5.6 times higher in two transgenic lines, B2-3-3-11 (T2) and B3-9-1-5 (T2), as compared to that in wild-type plants (Table 3). This suggested that biuret was decomposed in the roots and that 15N derived from biuret was built into more mobile compounds, such as amino acids, and transported into shoots. Taken together, biuret hydrolaseoverexpressing plants seemingly used biuret as an extra N source.