1) Graduate School of Agricukural and Life Sciences, University
of Tokyo, Tokyo, 113-8657 Japan
2) Graduate School of Bioagricultural Sciences, Nagoya University,
Nagoya, 464-8601 Japan
Dwarfism in rice has been studied
intensively. However, little is known about how panicle and internode interact.
We have observed that mutants with aberrant panicles tend to exhibit modified
cuhn length, especially shorter stature. Here we report the interaction
between the panicle development and the internode elongation using panicle/flower
mutants of rice.
We used 14 panicle/flower mutants
derived from Taichung 65 mutagenized with a chemical mutagen, N-methyl-N-nitrosourea.
Three of them (foni, di-supi and ur2) were reported earlier, and the other
11 mutants designated by the strain name (fm) were newly identified. These
mutants are classified into two groups by the stage at which the mutant
phenotype is first observed in panicle. The first group shows abnormalities
in the rachis and/or the rachis branches. Seven mutants, i.e. ur2, fm2O,
fm23, fm24, fm6O, fm6l and fm62, belong to this group. Among them, four
mutants, fm23, fmóO, fm6l and fm62, have short panicles. The second
group has defects in flowers such as modified organ number and change in
organ identity, and includes seven mutants,fonl, di-supi , fm2, fm4, fml4,
fm47 and fm55. First we measured the internode lengths of the mutants and
Taichung 65 as the wild type (Fig. 1). Most of the mutants had short stature.
Two mutants (ur2 and fm6O) showed the increased number of elongated internodes.
The internode elongation pattern in Fig. 1 indicates that the length of
the uppermost internode is affected in the mutants, but the lengths of
lower internodes are comparable to that of the wild type.
We analyzed how the lengths of internodes
are correlated with one another and how the panicle traits are related
to the internode length (Table 1). The table shows that the length of an
internode is positively correlated with that of the adjacent internode.
The lengths of first and second internodes from top are correlated with
each other, but not with those of the lower internodes. This suggests that
the elongation of lower internodes is regulated independently of that of
the upper ones.
The panicle length was significantly
correlated with the lengths of first and second internodes from top, but
not with the lengths of lower internodes. Other panicle traits (the numbers
of primary and secondary branches and the number of spikelets) showed a
significant correlation with only the uppermost internode length. Thus
the panicle development affects the elongation of upper internodes
To analyze how the internode elongation
pattern is associated with the type of mutants, principal component analysis
was carried out based on the data of internode lengths (Fig. 2). It is
clear that mutants defective in floral organs are distributed in the neighborhood
of the wild type, whereas most mutants with abnormalities in the rachis
and/or branches are positioned away from the wild type. These results indicate
that the early defects in panicle development severely modify the internode
elongation pattern.
The present analyses show that the
cuim length, especially the length of uppermost internode, is affected
by the early developmental mode of panicle in rice. Although the mechanism
by which panicle development affects the elongation of upper internodes
is still unclear, the elucidation of early panicle development is useful
for understanding of rice dwarfism.
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