BEIJING, CHINA
Institute of Genetics, Academia Sinica
The accumulation of lysine controlled by the o2 gene in QPM
--Mengqian Zeng, Yannan Liu, Taolan Yang and Songqing Ye

Thirty-eight samples of QPM (High-Quality Protein Maize) and normal maize were used as experimental materials. The normal maize, which had a normal nuclear gene background, was used as a control (CK). The experiments were carried out to analyze the accumulations of lysine controlled by the o2 gene. The leaf blade, leaf sheath, tassel branch, embryo and endosperm were used for
samples for biochemical analyses. The leaf blade and leaf sheath were taken at the 5-leaf stage, elongation stage and growing stage, but the tassel branch was taken at the growing stage, and the embryo and endosperm were taken at maturity. The samples were ground in a Waring blender and screened (100 mesh) until a fine powder was obtained. Every sample had three replications.

Amino acid compositions were analyzed by using an automatic and high speed amino acid analyzer (Model 835-50, Hitachi Ltd., Japan). The method of HCl hydrolysis was used in pretreatment of samples. Protein contents of samples were determined using Kjeldahl nitrogen determining apparatus.

Table 1. Amino acid composition of the embryo and endosperm in QPM and normal (g/100g protein).
 
Variety and part asp thr ser pro glu gly ala cys val met ile leu tyr phe lys nh3 his arg
T.T/o2                                    
embryo 9.1 3.6 5.0 5.6 15.0 6.1 6.7 - 5.9 1.1 3.2 6.7 2.7 4.4 6.4 1.7 3.7 11.0
endosperm 7.9 3.6 4.3 7.6 19.5 4.3 7.3 1.1 6.0 2.6 4.0 12.4 4.5 5.7 4.2 2.5 4.0 5.6
White dent                                    
embryo 9.7 3.9 4.6 3.3 12.6 6.1 6.9 0.7 5.6 2.2 3.4 7.2 2.9 6.6 7.3 1.7 4.1 9.6
endosperm 5.8 3.1 4.3 8.2 22.9 2.9 9.5 0.9 5.1 2.6 3.7 17.7 5.0 11.1 1.9 2.9 2.8 4.9

Table 2. Amino acid composition of the embryo and endosperm in QPM and normal (g/100g dry weight).
 
Variety and part asp thr ser pro glu gly ala cys val met ile leu tyr phe lys nh3 his arg
T.T/o2                                    
embryo 1.2 0.5 0.7 0.8 2.0 0.8 0.9 - 0.8 0.1 0.4 0.9 0.4 0.6 0.9 0.2 0.5 1.5
endosperm 1.1 0.5 0.6 1.0 2.7 0.6 1.0 0.1 0.8 0.4 0.5 1.7 0.6 0.8 0.6 0.3 0.5 0.8
White dent                                    
embryo 1.6 0.6 0.7 0.5 2.0 0.8 1.1 0.1 0.9 0.4 0.5 1.2 0.5 1.1 1.2 0.3 0.7 1.5
endosperm 0.7 0.4 0.5 1.0 2.7 0.3 1.1 0.1 0.6 0.3 0.4 2.1 0.6 1.3 0.2 0.3 0.4 0.4

Table 3. Protein content of the endosperm in QPM and normal (g/100g dry weight).
 
Type Variety and line Protein Content
QPM T.T/o2 13.06
  Syn. B/o2 10.3
  White HE/o2 9.1
  Yellow HE/o2 11.0
  Karmen/o2 11.8
Normal White dent 12.2
  Il287C 12.8
  Small eight rows 11.6
  Kunming yellow 13.1
  Yin 2 9.1
Waxy (1) Four-rows waxy (1) 10.8
  (2) Four-rows waxy(2) 14.2
  Purple stalk waxy 12.4
  Small yellow waxy 14.2
  Waxy maize 10.2
Coix Cultivar 14.6
  Wild species 19.4

Table 4. Amino acid composition of different fractions of endosperm proteins (percentage of no. gram molecules of total amino acid).
 
Variety asp thr ser glu gly ala cys val met ile leu tyr phe lys his arg pro nh3
Soluble protein                                    
Mo17 5.74 3.58 3.62 9.38 7.00 6.02 1.35 5.08 1.18 3.11 5.34   4.01 2.83 0.96 2.34 3.80 34.67
Mo17/o2 4.89 3.24 3.41 9.34 8.06 7.41 1.17 4.53 0.77 2.52 4.03   3.13 2.98 1.22 2.16 6.02 35.13
Yixi041/o2* 7.78 3.06 3.36 9.74 7.47 9.798 0.94 4.15 0.78 2.39 3.77   2.63 3.37 1.32 2.38 7.10 29.98
Yixi040/o2** 14.33 2.87 2.96 9.91 6.46 7.57 0.74 3.70 0.65 2.09 3.43 1.42 2.32 3.02 1.20 2.23 6.92 28.21
Zein                                    
Mo17 2.58 2.41 3.72 21.28 4.13 8.27 0.57 3.97   2.57 11.22 0.65 3.32   1.82 1.13 10.78 21.58
Mo17/o2 2.53 2.46 3.47 16.29 5.38 6.45 1.32 4.12   2.52 9.02   4.44   0.99 0.80 7.70 32.50
Yixi041/o2 2.97 2.42 2.98 10.87 4.97 4.65 2.32 4.41   2.54 6.73   2.95     0.95 5.30 45.95
Yixi040/o2 2.43 2.67 3.23 12.92 5.49 4.90 1.72 4.68   2.37 7.26   3.17   1.51   8.40 39.27
Glutelin                                    
Mo17 2.95 3.95 4.02 6.87 6.31 8.84 0.78 7.00   4.19 10.21 2.46 3.26 3.32 4.05 4.17 9.94 17.68
Mo17/o2 5.69 3.36 4.70 17.78 6.89 7.34 0.45 5.57   3.31 7.91 1.14 3.30 3.20 2.80 3.81 7.80 14.96
Yixi041/o2 5.73 3.42 5.03 19.28 7.35 7.78 0.31 5.49 0.10 3.31 8.33 0.81 3.21 3.04 3.31 4.24 8.33 10.92
Yixi040/o2 5.65 3.48 4.87 17.95 7.24 7.72 0.37 5.55 0.12 3.12 7.85 1.62 3.00 3.37 2.92 4.00 9.25 11.94
*QPM. Yixi044 and Yixi040 are sib lines.
**o2

The main results of the experiment were as follows:

(1) The o2 gene of QPM is a monogenic recessive. It controls the accumulation of increased lysine in endosperms, tassels and leaves at the seedling stage. The modifier factors and genetic background affect the physical properties of maize endosperms.

(2) More asp, gly, lys, arg and less pro, glu, leu, phe were observed in the embryo as compared with the endosperm of QPM and normal. The same situation was also observed in endosperms of QPM as compared with the endosperm of normal (Tables 1 and 2).

(3) Protein contents between endosperms of QPM and endosperms of normal showed almost no difference (Table 3). The amino acid composition analysis indicates that the soluble proteins and glutelins are rich in lysine, while the zeins are almost devoid of lysine. The endosperm protein fractions of QPM show no more lysine than normal (Table 4). The endosperm of QPM contains more glutelin and less zein that normal.

(4) Twelve inbred lines of QPM, and a few heterotic hybrids of QPM, were developed.


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