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Rice Genetics Newsletter 96
10. Developmental timing of phenotypic expression in a mutant
with twisted leaf
Y. Iroh1, I. Takamure1 and S. SHIBATA2
Rice shows a striking feature that the phyllochron (the interval
of leaf emergence) is synchronized with the plastochron (that of leaf initiation)
as reviewed by Nemoto et a!. (1997). To understand rules of the shoot development
as the dynamic process, visual markers reflecting the progress of shoot
development is quite useful (Poethig 1988). However, it is needed to accumulate
information on changes in genic expressions depending on the order of phyllochron
in order to understand of the shoot development of rice. Here, we describe
a mutant with twisted leaf blade that produces malformed leaf blades only
in the later stages of vegetative development.
A mutant line, DSK1 15 with malformed leaf blade, was derived
from the anther culture of hybrid derivatives among 3 early-heading cultivars,
Kirara 397, Kinuhikari and Hayakaze. Since the trait showed a simple inheritance,
the mutant gene was tentatively named tl(t) (Shibata et al. 1997). It was
noticed that the degree of the malformation seemed to become severe as
the shoot development progressed, although typical malformed leaves were
not observed in the basal phytomers.
The developmental timing of phenotypic expression was investigated
under different temperature regimes (17°C and about 27°C). Number
of days till emergence of flag leaf was 101.0± 0.0 and 62.0±
1.4 at 17°C (n=6) and at about 27°C (n=8), respectively. Although
the growth duration varied significantly under the two conditions, total
number of leaves produced on the primary shoot showed no significant difference
under the two conditions (11.0±0.0 at 17°C and 11.1±0.3
at about 27°C). Thus, the two temperature conditions made it possible
to examine the timing of phenotypic expression when only the time duration
of vegetative growth changes.
The malformed leaf blade was readily recognized from the
asymmetrical location of midvain, and the degree of malformation was rated
from 1 to 3 according to the seventy as shown in Fig. 1. In case of the
severely malformed phenotypes, the malformed leaf blades were also recognized
from distortion in the leaf edge. Apparently normal-like leaf blades with
symmetrical location of midvain as well as straight leaf shape were rated
as 0. In spite of the difference in the growth duration under the two conditions,
malformed leaf
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blades were first recognized in the 6th phytomers, and then
the degree of malformation increased linearly till the formation of flag
leaf. Apparent abnormality was not observed in morphologies of panicles
and flowers. The results showed that the timing of the phenotypic expression
is dependent not on time but on space. Based on histological observations
in DSK1 15, inflorescence initiation seemed to occur around the leaf age
of 7.0. To look into if the expression oft! (t) might be associated with
the transition from vegetative to reproductive stage, it is needed to examine
the timing of phenotypic expression when the number of phytomers is changed
before inflorescence initiation.
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