3.1 Biuret injury in hydroponically grown rice seedlings
We first investigated the biuret sensitivity of wild-type rice plants. When wild-type Nipponbare seeds were sown in culture solutions supplemented with varying levels of biuret (0, 0.1, 0.3, and 1.0 mmol L-1 biuret), germination was not inhibited, regardless of the biuret levels. The plant height of 7-day-old seedlings decreased with increasing concentrations of biuret (Figure 1a). Chlorosis was observed in some plants exposed to 0.1 mmol L-1 biuret and all plants exposed to 0.3 mmol L-1 biuret. It was most markedly observed in leaf blades of the emerging third leaf. In plants exposed to 1.0 mmol L-1 biuret, chlorosis was less prominent, probably because of the severe reduction in the growth (Figure 1b).