The S1-60 mutant, isolated from an ethyl methanesulfonate
(EMS) mutagenized japonica cultivar Nipponbare, is characterized
by brittle culms and leaves that can be easily broken by bending (Fig. 1A and B). In order to describe this phenotype precisely, we
measured the breaking force and elongation length of the first and
second internodes of wild-type and mutant. These two parameters
define the force required to break the culm segment and reflect the
elasticity of plant tissue, respectively. As shown in Fig. 1C and D,
the breaking force of the first and second upper internodes of S1-
60 mutant was reduced by 84% and 88% compared with that of the
wild-type plants, respectively. Meanwhile, the elongation length
of the first and second upper internodes of S1-60 mutant was also
reduced by 34% and 53% compared with that of the wild-type plants
(Fig. 1E and F), respectively. The significant decrease in the breaking
force and elongation length of S1-60 mutant suggested that
mutation in S1-60 strongly affects the mechanical strength of rice
plant.