Amylose content is one of the most important factors affecting the cooking
and processing behavior of rice. Amylose is synthesized by granule-bound
starch synthase (GBSS); the expression level seems to control the amylose
content (Sano 1984). This paper deals with the genetic variation of GBSS
level in Myanmar local rice cultivars.
A total of 350 local rice cultivars were obtained from the Seed Bank of
Myanmar. Kinmaze, IR36 and their respective waxy mutants, EM21
and EM2009, were used as controls. Sodium dodecyl sulphate-polyacrylamide
gel electrophoresis (SDS-PAGE) of crude proteins extracted from seed samples
were performed by the method of Laemmli (1970). Apparent amylose content
in endosperm starch was colorimetrically determined by DU 7500 Spectrophotometer
Kinmaze and IR36 showed low and high GBSS level, respectively. GBSS were
absent in their waxy mutants. Myanmar local rice cultivars were
classified into four types of GBSS levels; high, intermediate, low and
absent, based on staining intensity of 60 kD band and western blot analysis
using antiserum raised against the waxy protein from wheat endosperm (Figs.
1A and B). This result indicates that GBSS level is diverse in Myanmar
local rice cultivars.
The apparent amylose content of Myanmar local rice cultivars varied from
0 to 30%. The 350 accessions analyzed were classified into five apparent
amylose content groups: waxy (0-6%), very low (6-12%), low (12-18%), intermediate
(18-24%) and high (>24%). The relationship between GBSS level and the
apparent amylose content was investigated by half seed
analysis (Fig. 2). Amylose content ranged from 0 to 8% among the cultivars
without GBSS, and from 6 to 24% among cultivars with low level of GBSS.
Cultivars with intermediate and high levels of GBSS had 6 to 24% and 13
to 30% amylose content, respectively. Apparent amylose content estimated
by colorimetric method was influenced not only by net amylose content
but also by fine structure of amylopectin (Nishi et al. 2001).
The amylopectin structure is clearly different between japonica
and indica rice cultivars (Nakamura et al. 2002). Variation
in apparent amylose content of Myanmar local rice cultivars may be caused
not only by net amylose content but also by amylopectin structure, even
though each GBSS level shows variation in apparent amylose content.
The regional distribution pattern of GBSS level is shown (Table 1). Cultivars
with intermediate GBSS level were localized in three mountain regions,
i.e. Western Mountain Region (WMR), Northern Mountain Region (NMR) and
Eastern Mountain Region (EMR). Cultivars showing high level of GBSS were
widely distributed throughout; 59% of Myanmar local rice cultivars belong
to this type. Variation in GBSS level of cultivars from the three mountain
regions was much wider than these from other regions.
These results suggest that the mountain regions in Myanmar are important
the genetic resources of amylose properties, as reported by Nakagahra
We thank Dr. N. Fujita, Faculty of Bioresource Sciences, Akita Prefectural
University, for the gift of antiserum raised against the waxy protein
of wheat endosperm.
Laemmli, U. K, 1970. Cleavage of structural proteins during the assembly
of the head of bacteriophage T4. Nature 227: 680-685.
Nakagahra, M., 1978. The differentiation, classification and center of
genetic diversity of cultivated rice (Oryza sativa L.) by isozyme
analysis. Trop. Agri. Res. Ser. TARC 11: 77-82.
Nakamura, Y., A. Sakurai, Y. Inaba, K. Kimura, N. Iwasawa, T. Nagamine,
2002. The fine structure of amylopectin in endosperm from Asian cultivated
rice can be largely classified into two classes. Starch / starke. 54:
Nishi, A., Y. Nakamura, N. Tanaka, H. Satoh, 2001. Biochemical and genetic
analysis of effects of amylose-extender mutation in rice endosperm.
Plant Physiol. 127: 459-472.
Sano, Y., 1984. Differential regulation of waxy gene expression in rice
endosperm. Theor. Appl. Genet. 64: 467-473.