Rice management and sampling
Selected seeds of IR68144 and IR64 were packaged with gauze and germinated in a glass beaker for 2 days in the dark, and then transferred into quartz sand. The 5-leaf seedlings were transplanted into a 10-L plastic bucket with three hills in each bucket and three seedlings per hill. The bucket was flooded at two days before rice transplanting, and rice management was similar as that in the paddy field. Each treatment was replicated thrice and all treatments were arranged randomly. The shoots of rice were cut with a pair of stainless steel scissors at the harvesting stage. Each rice shoot was partitioned into culm, flag leaf, non-flag leaves, peduncle, grain hull and brown rice. All samples except grain were rinsed with tap water firstly and then washed with deionized water.