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Afzal, M., M. Kawase, H. Nakayama, and K. Okuno. 1996. Variation in electrophoregrams of total seed protein and Wx protein in foxtail millet. p. 191-195. In: J. Janick (ed.), Progress in new crops. ASHS Press, Alexandria, VA.

Variation in Electrophoregrams of Total Seed Protein and Wx Protein in Foxtail Millet

Muhammad Afzal, Makoto Kawase, Hiroki Nakayama, and Kazutoshi Okuno


  1. METHODOLOGY
  2. RESULTS
    1. Intraspecific Variation and Geographical Distribution of Total Seed Protein
    2. Intraspecific Variation and Geographical Distribution of Wx Protein
    3. Variation and Geographical Distribution in Foxtail Millet in East Asia
  3. SUMMARY
  4. REFERENCES
  5. Table 1
  6. Table 2
  7. Fig. 1
  8. Fig. 2
  9. Fig. 3
  10. Fig. 4

Foxtail millet (Setaria italica Beauv.) was one of the crops which was domesticated in the early stages of agriculture and has been cultivated across Eurasia continent from tropical to temperate regions. Today it is a staple food in India and northeastern China.

Intraspecific variation of foxtail millet and its geographical distribution has been discussed on the basis of protein polymorphism by de Wet et al. (1979). They suggested a mechanism for domestication due to germplasm exchange based on a comparison of the variation in seed storage proteins of wild and cultivated species of Setaria from western Europe, Afghanistan, and East Central China. Jusuf and Pernes (1985) studied the genetic diversity of landraces collected from East Asia, India, the former U.S.S.R and Europe using discriminant analysis of data scored for 10 isozyme loci and found clear regional differences among samples tested.

Starch granule bound polypeptide, Wx protein, is responsible for amylose production and has been detected as a single band of approximately 60 kDa in maize (Echt and Schwartz 1981), rice (Sano 1984), grain amaranths (Konishi et al. 1985) and potato (Hovenkamp-Hermelink et al. 1987). In foxtail millet, accessions showing low amylose content in endosperm starch were found in Japan, Taiwan, Philippines, and Indonesia (Takei et al. 1989). Nakamura et al. (1990) detected Wx protein in a few Japanese landraces of foxtail millet, which were glutinous, non-glutinous and low amylose strains. A close relation between amylose content and level of Wx protein was recognized.

This report deals with intraspecific variation and the geographical distribution of total seed protein and Wx protein in foxtail millet landraces.

METHODOLOGY

A total of 217 landraces of foxtail millet were used in this study (Table 1). SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of crude proteins extracted from seed samples followed the method of Laemmli (1970). Starch granule bound protein (Wx protein) was isolated and analyzed using SDS-PAGE (Echt and Schwartz 1981). Amylose content in endosperm starch was colorimetrically determined on a dry weight basis using Autoanalyzer II (BRAN+LUEBBE).

RESULTS

Intraspecific Variation and Geographical Distribution of Total Seed Protein

Variation in electrophoregrams of total seed protein was observed in the range of 20 to 30 kDa and about 60 kDa. Based on the combination of 4 protein bands (Fig. 1 a,b,c and d) detected between 20 and 30 kDa, landraces were classified into six different types based on electrophoregrams (Fig. 2). They were designated protein type A (with bands a,b,c), type B (b,c), type C (a,b), type D (c), type E (b), and type F (b,d). A geographical cline of SDA-PAGE electrophoregram was observed, despite the limited number of landraces from Thailand, Myanmar, and Indonesia (Table 1). Distribution of type A is confined to India and countries to the west. Type B, the second most frequent type, is distributed in East Asia, except for Japan and Korea, and west of Pakistan. Type C is found in Japan and Europe. Type D is distributed in China, Taiwan, and Indonesia. Type E is the most common type and widespread throughout Eurasia. Type F occurs in Japan, Korea, and China. Landraces from India and Pakistan were relatively uniform for protein types.

Intraspecific Variation and Geographical Distribution of Wx Protein

All landraces analyzed could be classified into three groups based on the level of Wx protein. One group had a thick band, a second group a thin band (Fig. 3) and a third group no band. Amylose content of each group was 20 to 35% (non-waxy), 8.5 to 15.6% (intermediate), and close to 0% (waxy) respectively, and corresponded to the visual estimate of level of Wx protein. The intermediate and waxy groups were found only in East Asia and Southeast Asia (Fig. 4), which is in agreement with the previous report by Sakamoto (1979) and Takei et al. (1989).

In addition, the distribution of these groups is similar to the geographical distribution of waxy endosperm found in six other crop species described by Sakamoto (1982). The regulatory mechanism of the intermediate type is not clear. A regulatory gene (du) lowering Wx protein level and amylose content has been found in rice (Okuno et al. 1983). Lowering amylose content is considered to be controlled by alleles at wx locus or any independent loci of wx locus. Gene(s) controlling intermediate level of Wx protein and low amylose content (whether du-like trans-element or Wx allele) should be genetically examined.

Variation and Geographical Distribution in Foxtail Millet in East Asia

Based on the polymorphism of total seed protein, the center of diversity could not be clearly identified. As mentioned above, types A,D and F distributed particularly in the western half of Eurasia, Taiwan and Philippines, and East Asia, respectively. Out of 18 possible phenotypes based on the variation in total seed protein and level of Wxprotein, thirteen types were observed (Table 2) and five or six of all the phenotypes existed in Taiwan, Japan, and China. Positive type for phenol coloration was primarily found in Taiwan, Philippines, Nepal, and India (Kawase and Sakamoto 1982 Table 2). Jusuf and Pernes (1985) suggested six regional groups including China-Korea-Japan, Taiwan-Okinawa islands of Japan, India-Kenya, former U.S.S.R., Central Europe, and France, according to discriminant analysis for 10 isozyme loci. Furthermore, most landraces from China, Korea, and Japan (except for the Okinawa islands) belong to the same group for hybrid sterility, while major part of those from Taiwan and Okinawa were included in different group (Kawase and Sakamoto 1987).

SUMMARY

Variation in electrophoregrams of total seed protein was observed in the range of 20 to 30 kDa and about 60 kDa in 217 landraces of foxtail millet collected across the Eurasia. Based on the combination of 4 protein bands (Fig. 1 a,b,c, and d), landraces were classified into six different types (Fig. 2). A geographical cline of electrophoregrams was observed (Table 1). Based on the level of starch granule bound polypeptide (Wx protein), these 2l7 landraces weredivided into, non-waxy, intermediate, and waxy starch types (Fig. 3). The intermediate and waxy types were found only in East Asia and Southeast Asia (Fig. 4).

REFERENCES


Table 1. Variation in SDS-PAGE electrophoregram of total seed protein of foxtail millet.

Electrophoregramsz
Origin No. of strains
examined
A B C D E F
Japan 12 -- -- 2 -- 7 3
Okinawa (Japan) 4 -- -- -- -- 4 --
Korea 9 -- -- -- -- 8 1
China 14 -- 5 -- 1 7 1
Taiwan 14 -- 2 -- 4 8 --
Philippines 5 -- 3 -- -- 2 --
Indonesia 1 -- -- -- 1 -- --
Thailand 2 -- -- -- -- 2 --
Nepal 4 -- -- -- -- 4 --
India 10 1 -- -- -- 9 --
Pakistan 120 1 108 -- -- 11 --
Afghanistan 5 -- 1 -- -- 4 --
Central Asia 6 1 2 -- -- 3 --
Europe 11 2 5 2 -- 2 --
Total 217 5 126 4 6 71 5
zA (bands a,b,c), B (b,c), C (a,b), D (c), E (b), F (b,d) respectively.


Table 2. Observed protein phenotypes based on the variation in total seed protein and level of Wx protein.

Electrophoregrams
Wx protein level A B C D E F Total
Waxy 0 2 2 3 17 3 27
Intermediate 0 3 0 1 3 0 7
Non-waxy 4 114 1 0 38 1 158z
Not determined 1 7 1 2 13 1 25
Total 5 126 4 6 71 5 217
z120 accessions were from Pakistan.


Fig. 1. Four polymorphic band analyzed in electrophoregram of total seed protein. Fig. 2. Intraspecific variation of total seed protein in foxtail millet.

Fig. 3. Electrophoregram of Wx protein from non-waxy and intermediate type of endosperm.


Fig. 4. Geographical distribution of three types of Wx protein in foxtail millet landraces.

Last update August 15, 1997 aw