4. Discussion
It is now clearly established that grain quality is a function of grain composition, principally in
proteins, which depends on the genotype and the environment. The genetic effect is mainly reflected
by qualitative variation such as protein polymor- phism and secondly by quantitative variation of
total protein or of different units and subunits. In contrast, the environmental effect growing sea-
son, site, fertilisation,.... was mainly reflected by the quantitative variation, such as in total protein
or protein unit and subunit contents.
In our experiment, the quantity of nitrogen per grain exhibited a higher variation than grain
weight. However, despite the relative indepen- dence of these two variables their ratio, the
protein content PC in dry matter, essentially reflects the variation in protein amount, and the
use of two variables, the content or the amount was nearly equivalent. Figs. 3 and 4.
It is not surprising that the quantity or the content of two major classes of storage proteins,
gliadin and glutenin, is significantly related to total protein, modified essentially by the nitrogen
supply fertilisation and site. The significant ‘facts’ are firstly, the difference between the two
classes and secondly, the varietal behaviour.
If the quantity of nitrogen or protein per grain increases, the gliadin to glutenin ratio in-
creases to a maximum potential if PT = equal to the ratio between two regression slopes Fig. 4.
Finally, an increase in the gliadin to glutenin ratio with the nitrogen quantity per grain Fig. 5 or
content , data not shown was obtained. Simi- lar results were also found by several authors,
despite different methods of analysis of proteins Blumenthal et al., 1993; Jia et al., 1996a,b.
In all cases, for the same quantity or protein content, there is a significant varietal effect only
on the glutenin fraction: in Rinconada, glutenin is higher than in the Bancal variety Table 1, prob-
ably owing to the difference in allelic composition and expression in the two varieties. This is in
agreement with the results of Autran 1990 which showed a increase in the percentage of HMW-GS
in total protein with the number of HMW-GS, and Halford et al. 1992 who showed that the
presence of subunit 1A × 1 or 1A × 2 increased the proportion of HMW-GS by about 2 in
comparison
with a
null allele.
However, Rinconada has 5 HMW-GS 1, 7 + 8, 5 + 10 and
Bancal has 4 HMW-GS 7 + 9, 5 + 10. More- over, MacRitchie and Gupta 1993 indicated a
similar quantity of HMW-GS produced by the loci of alleles GluB1 and GluD1, such that the
quantitative superiority of Rinconada could be partially attributed to the quantitative effect pro-
duced by the presence of GluA1. We also noted that the total protein content per grain was not
different between the two varieties Table 1; thus, the increase in glutenin content in Rinconada is
not accompanied by an increase in total N quan- tity but more probably by a different allocation of
Fig. 7. Variation in the percentage of three LMW-GS peaks as a function of the amount of LMW-GS in Rinconada. Data
consist of means of two sites Torregrossa and Bell.lloc, 2 years 1994 – 1995 and 1995 – 1996 and three N fertilisation
rates 0, 100 and 200 kg Nha. Units of area are mVmin.
Table 4 Environmental effect on LMW-glutenin composition: RP-HPLC peak characteristics
Bancal Variety
Rinconada Retention
Amount Percentage
Peaks Retention
Amount Percentage
area area
a
time time
of LMW r with LMW
of LMW r with LMW
16.3 10.6
– Pool
45
–
48
15.09 8.3
− 0.76
2.69 1.7
– 46
45.6 45.9
1.94 1.1
– 0.37
0.3 –
46.4 46.5
3.37 46 –5
1.8 –
47.2 47
6.87 4.4
– 46.8
2.41 1.3
– 0.23
0.1 –
47.4 47.6
2.05 47 –5
0.1 –
6.17 4.0
– 48.7
48 5.3
48.6 2.9
– 17.68
11.54 –
9.51 Pool
49
–
50
5.1 −
0.52 17.68
11.5 –
49.3 49
4.97 49.5
2.6 –
– –
– 49.8
– 4.55
49 –7 2.5
– 20.25
13.0 0.46
50.6 51
13.07 50.8
6.7 0.56
21.56 13.9
– 73.38
Pool
51
–
52
37.7 0.70
– 51 –5
– –
– 51.5
46.91 24.0
– 21.56
13.9 –
52.0 52.0
26.47 52
13.7 –
32.23 21.1
– Pool
52
–
53
30.95 16.4
− 0.52
11.81 7.6
– 52.7
52.6 13.08
52 –7 6.8
– 20.41
13.5 –
53.0 53
17.87 53.0
9.6 –
0.837 0.5
– 53.8
53.8 8.14
53 –9 4.5
− 0.43
23.81 15.4
– 54.7
54 21.10
54.9 10.8
0.91 2.87
2.0 –
56.1 56.1
11.43 56
6.1 −
0.57 18.28
11.7 –
Pool
58
–
59
8.39 4.3
– 8.70
5.6 –
– 57.8
– 58
– –
9.58 6.0
0.46 58.5
7.01 3.7
– 58 –5
58.5 –
– –
59.3 1.38
0.6 –
– 59
a
Area is given in mVminmg flour. Statistical significant at PB0.05.
Statistical significant at PB0.01.
N, in favour of glutenins and at the expanse of
soluble fractions,
albumin, globulin
or amphyphiles.
Concerning the variation in glutenin composi- tion, the content of LMW- and HMW-GS was
closely related to that of glutenin. The slope of regression between LMW-GS and total glutenin
content Fig. 6; 0.69 was two times greater than that of HMW-GS 0.31. When calculating this
regression with the data on varietal effect of Nico- las 1997 we obtained similar values, 0.33 for
HMW-GS and 0.67 for LMW-GS. Moreover, in both experiments the constant term of regression
was positive for HMW-GS and negative for LMW-GS. This resulted a decrease in both the
relative
contribution of
HMW-GS to
total glutenin content and of the ratio HMW-GS
LMW-GS with the increase in total glutenin con- tent. However, in our experiment this ratio was
not significantly affected, despite a high variation from 0.34 to 0.70 with a coefficient of variation of
11.9 Table 2. A similar amplitude of variation was observed by Nicolas 1997 and Pechanek et
al. 1997. Nevertheless Pechanek et al. 1997 showed a increase of this ratio with protein con-
tent. This contradiction may be due to differences in the methodology used, or to the factor that
induced the variation and the interaction with the genotype. For example, Daniel et al. 1998a,b,
clearly showed that two environmental factors, temperature and nitrogen supply, acted differ-
ently: high temperature increased the proportion
of HMW-GS in total glutenin whereas an increase in nitrogen supply decreased the proportion of
HMW-GS. Our data also showed a different behaviour of
the genotype. The Bancal cultivar has a more stable HMW-GS composition than Rinconada.
Indeed, with an increase in HMW protein, the proportion of different peaks did not change in
Bancal but did in Rinconada Table 3. This general pattern of variation also characterises the
LMW-GS composition: stability in Bancal and some changes in Rinconada. The cause of this
different genetic behaviour is not known.
Concerning the variation in gliadin composi- tion, we noted that as in glutenin, the content of
different gliadin pools were closely related to gliadin content.
In our experiment, the proportion of the v-sub- group TR B 39 min in total gliadins was about
5 Bancal and 11 Rinconada, where the lower value was observed in Bancal, in which the
faster gliadins v5- were missing. There was a good agreement between these values and those
noted by Wiesser et al., 1994. The proportion of the a + b gliadins 39 B TR B 53 was 60 – 64,
and that of the l-gliadins 29 – 31, respectively, for the Rinconada and Bancal varieties. Similar
values were obtained by Wiesser et al. 1994 and Pechanek et al., 1997.
As in glutenins, all these gliadin subunits and their constituent peaks were highly correlated
with total gliadin content. Their contribution to the total gliadin pool was very variable: the pro-
portion of certain peaks was stable whereas the contribution of other peaks was related to the
variation in gliadin content Table 5 Fig. 9. But, in contrast to glutenin, there are not different
behaviour of two varieties in the variation of the proportion of gliadin peaks in the total gliadin.
To understand how the environment can change grain composition and to forecast this
change, Triboi and Triboı¨-Blondel 1998 devel- oped a concept to analyse the variation in grain
composition: every change is a consequence of the mechanisms of nitrogen allocation between differ-
ent types of protein, through the change in rate and duration of synthesis. Thus, the quantity of
one compound ‘Q’ is dependent on the rate of synthesis r and on the duration of synthesis
Fig. 8. Variation in the percentage of three LMW-GS peaks as a function of the amount of LMW-GS in Rinconada. Data consist of means of two sites Torregrossa and Bell.lloc, 2 years 1994 – 1995 and 1995 – 1996 and three N fertilisation rates 0, 100 and 200
kg Nha. Units of area are mVmin.
Table 5 Environmental effect on gliadin composition: RP-HPLC peak characteristics
Variety Rinconada
Bancal Amount
Percentage Percentage
Retention Retention
Peaks Amount
area
a
area
a
time time
of GLI r with GLI
of GLI r with GLI
Pool
19
–
22
– –
– 18.4
8.3 0.46
– –
– 19.3
– 4.9
19 2.3
– –
21 –
– –
21.6 10.7
4.8 0.48
– 22
– –
– 22.9–23.2
2.8 1.3
0.48 4.5
2.0 0.57
29.1 29.2
5.3 29
2.3 0.71
6.0 2.7
– Pool
33
–
34
1.1 0.4
2.8 1.3
– –
30.4–32.9 –
33 –
– 33.1–33.9
34 3.2
1.4 –
34.5 1.1
0.4 –
– 37.3
37 0.8
– 0.3
0.51 5.4
2.4 –
Pool
39
–
41
4.3 1.9
39.0 39
1.9 0.9
– 39.5
0.9 0.4
40.7 41
3.5 1.5
– 41.0
3.4 1.5
– 29.8
13.2 –
42.2 42.3
28.0
42
13.0 0.66
Pool
43
–
46
54.7 24.5
– 43.5
20.1 –
43.6 43
9.3 4.2
– 43.5
3.6 1.6
– 13.5
6.0 0.44
44.5 44.6
11.2 44
5.1 0.42
18.4 8.2
– 44.9
17.2 7.9
– 45
44.9 13.6
6.2 −
0.63 46.0
46.2 11.6
46 5.4
− 0.47
Pool
47
–
51
53.8 24.3
− 0.75
52.7 24.6
− 0.61
21.5 9.8
− 0.74
47.9 47
8.3 47.9
3.9 4.5
2.0 –
48.1 48.5
21.4 48
10.0 −
0.61 49.2
49 23.0
10.4 −
0.70 49.0
17.8 8.3
– 50.8
51 4.8
2.1 –
50.6 5.2
2.4 −
0.46 29.3
13.2 –
52.4 Pool
53
–
54
24.7 −
0.65 53.3
53 20.5
9.3 −
0.55 53.1
15.3 7.3
– 54.5
54 8.8
3.9 –
53.6 25.4
12.0 –
5.7 3.6
– –
Pool
55
–
59
– –
– –
– 55.0
8.4 3.9
− 0.46
55 –
1.2 0.5
– 56.6
56.6 3.1
57 1.4
0.68 56.9
58 1.5
0.7 −
0.64 –
– –
1.0 0.4
0.52 –
58.5 –
58.0 –
0.6 0.3
– –
58.4 –
59 –
– 59.4
59.5 1.4
0.6 –
– –
– –
31.6 14.0
Pool
60
–
62
0.46 9.3
4.3 –
14.4 6.4
0.46 58.5
59.8 2.0
60 1.0
60.6 61
1.0 0.5
− 0.67
59.6 3.3
1.6 16.2
7.1 62
0.61 61.5
61.2 4.0
1.7 0.60
a
Area is given in mVminmg flour. Statistical significant at PB0.05.
Statistical significant at PB0.01.
D: Q = rD + k. Consequently, to forecast the quantity of one
compound ‘Qc’ or the ratio between two com- pounds, it is necessary to estimate three parame-
ters: rate of synthesis, onset time and duration or stopped date. In a particular case of two storage
compounds c
1
and c
2
which have same onset time, the
Qc
i
= r
ci
Dc
i
In consequence, if the deposition rate is con- stant, the ratio between the compounds formed at
the same time stay constant during grain filling, equal to the ratio between the two rate of synthe-
sis, r
1
r
2
, despite a different synthesis rate and quantity deposited. However, the final ratio de-
pends on the date of cessation of synthesis, or on the duration of filling:
r
f
= r
1
D
1
r
2
D
2
In contrast if the onset time is different, the ratio Q
1
Q
2
changes during filling period. This is a new conceptual approach to analysing grain com-
position formation and to comparing the few data on environmental effect.
5. Conclusion
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