Plant materials and growth conditions
Seeds of japonica rice (Oryza sativa ) cultivar Nipponbare
were purchased from Nouken (Kyoto, Japan). Transgenic rice lines
overexpressing bacterial biuret hydrolase were developed from
Nipponbare (Ochiai et al., 2020),
and the T3 generation was used in this study. Seeds of
rice were soaked in distilled water added with fungicide (Trifumin;
Nippon Soda, Tokyo, Japan) for two days. Ten seeds were sown on a mesh
(18 mesh, 23 x 34 mm) stretched on a plastic slide mount and floated on
a culture solution. The culture solution contained 1 mmol
L-1(NH4)2SO4, 0.5 mmol
L-1 KCl, 0.25 mmol L-1KH2PO4, 0.5 mmol L-1CaCl2, 0.5 mmol L-1MgCl2, and Arnon’s micronutrient (cited by Hewitt,
1966). Iron was supplied at the rate of 5 mg Fe L-1 as
Ethylenediamine-N,N,N’,N’-tetraacetic acid iron(III) sodium salt. Biuret
was added to the solution whenever necessary. The culture solution was
prepared with tap water and not aerated. At most, six nets were floated
in a 1-L plastic container. Plants were raised in a growth chamber
(NS-280 FHW; Takayama Seisakusyo, Kyoto, Japan) under the following
conditions: temperature, 30°C; photoperiod, 12 h; and light intensity,
350 μmol m-2 s-1.
The rice Oc cell suspension culture line (Baba et al., 1986) was
provided by RIKEN BRC, participating in the National BioResource Project
of the MEXT/AMED, Japan. The cells were maintained as described by
Ochiai et al. (2020).