3.4 Biuret tolerance in transgenic rice plants overexpressingbiuret hydrolase
Rice plants overexpressing biuret hydrolase showed improved tolerance to biuret (Figure 4). The plant height of 9-day-old wild-type rice seedlings was reduced or remained unchanged with the addition of 0.3 mmol L-1 biuret, though it was significantly increased in two transgenic lines (Table 2). Similar results were also obtained for the chlorophyll content observed in leaf blades of the third leaf. The chlorophyll content in wild-type plants decreased significantly in the presence of excessive biuret levels, but increased in B3-9-1 plants, and remained unchanged in B2-3-3-3 plants (Table 2). These results clearly showed that rice plants overexpressing biuret hydrolasegained tolerance to biuret toxicity through the decomposition of biuret in plants.