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Carbohydrate Content and Grain Growth in Wheat and Barley
11"
Biochem. Physiol. Pflanzen 169, S. 437 -446 (1976)
Carbohydrate Content and Grai·n Growth in Wheat and Barley P. APEL and L. NATR Zentralinstitut fiir Genetik und Kulturpflanzenforschung der AdW, Gatersleben and Institute of Cereal Crops, Kromeriz, CSSR Key Term Index: assimilate storage, grain growth, sink-source relation; Hordeum spec., Triticum spec.
Summary The time course of grain growth and the content of ethanol soluble substances in the culm in spring barley, spring wheat and winter wheat were investigated. The maximum value of sugars in the culm was reached about 5 days before the maximum of the growth rate of kernels. From the results it was concluded that temporary storage of assimilates in the culm assures optimum grain growth also under unfavourable conditions for photosynthesis. Under the given experimental conditions grain growth was not limited by assimilate supply in the early stages of development.
Introduction
The dry matter accumulated in cereal grains comprises hoth the assimilates currently produced in the photosynthesizing organs and assimilates temporarily stored. The storage capacity for photosynthetic products of stem and also leaf tissue is fairly high (YOSHIDA 1972; APEL et al. 1973; SLUSARCZYK and WOJCIESKA 1974; SPIERTZ 1974). This may be deduced from the fact that shortly after anthesis the assimilate production is very high and kernel growth, i. a., rate of dry matter accumulation in the kernels is negligible. Some contrary results published in the last decade may be understood as special cases of the relationship between assimilate production, temporary storage and demand of assimilates for grain growth and respiration. For example, the correlation between the demand of assimilates in the ear and the rate of flag leaf photosynthesis (KING et al. 1967) could indicate that under the given experimental conditions the capacity of the plants for temporary assimilate storage was fully saturated. On the other hand, the non-existence of any dependence of leaf photosynthesis on the assimilate demand in sink organs (NOSBERGER and THORNE 1965; LUPTON 1968; THORNE 1972; APEL and PEISKER 1972; APEL et al. 1973) indicates that there is no control over photosynthesis by the non-saturated pool of assimilates. Therefore one could expect a wide range of relationships between sink and source depending on growth conditions before grain development and on varietal characters. The quantitative description of the course of the grain growth and its comparison with changes in the amount of soluble substances in the stem as presented in this paper attempt to provide basic information necessary for further investigation.
I
II,
III
438
P. APEL and L. N1.TR
Material and Methods Material. - Spring barley: Diamant, Ametyst, KM 1192. Diamant and Ametyst are varieties from the CSSR, KM is a breeding line from CSSR. - Spring wheat: Carola. This variety was bred in GDR anll successful in the sixties. - Winter wheat: Kavkas, Charkovska, Mironovskaja 808, Pilot, Derenburger Silber. Kavkas, Charkovska and Mironovskaja 808 are modern varieties from Soviet Union, Pilot is a modern and Derenburger Silber an old variety from GDR. The varieties were grown 1974 in the experimental fields at Kromeriz and Gatersleben, only Kavkas and KM in both locations. (Kromeriz: 48°18' degrees of latitude, 17°23' degrees of longitude; height above sea level 204 m; average year precipitation 599 mm; average day temperature 8,6 °C, Gatersleben: 51°49' degrees of latitude, 11°17' degrees of longitude; height above sea level 110 m, average year precipitation 492 mm; average day temperature 8,4 °C.) During anthesis about 200 culms bearing ears of the same developmental stage were marked. On the 10th day after anthesis the first sample of 15 culms was harvested. Further samples were taken in regular intervals of 5 days till full maturity. The culms of each harvest were divided into grains (by dissecting them out from the ears) into leaves (blades and sheath) and culms. The fractions were dried at 110°C during the first two h and at 65°C during the following two days and finally their dry weight was determined. Analysis. - The pulverized material of the culms was subsequently extracted three times with hot 80 % ethanol. The amount of ethanol soluble substances (e.s.s.) was calculated as the difference between the culm dry weight before and after extraction. In some cases sugar and starch content was determined using a modified procedure of MCCREADY et al. (1950). Mathematical description of grain grwoth. - For mathematical description of the kernel dry weight changes from anthesis to maturity Richards' comprehensive growth function was used (RICHARDS 1959, 1969). Here, the growth rate is given by dW -=a·Wm+b·W
dt
W = dry weigth, a, b, and m are parameters. The integral of this function is 1
W,t) = [ (ila + Wol-m ) • eb . t· (l-m) _ila]l-m Wo is the dry weight at zero time. The parameters a, b, m, and Wo were computed from the empirical data by a least square method (APEL et al. in press). From the function the time course of absolute and relative growth rates was calculated as well as the following values: computed saturation level for the kernel growth curve. W max is nearly identical with the WmBX mean of empirical values of the last two or three samplings. maximum of the first derivative of the growth curve (mg. grain-I. d- l ). This value W'max indicates maximum growth rate of the grains. average relative growth rate for the time between 10 % and 90 % dry weight using the formula: (In W90% - In W10%) t90% - t 10% Dw50% and D w90 % - number of days from anthesis till the time when grain dry weight reaches 50 % and 90 % of its final weight, respectively. T w50% and T w90% the sum of daily mean temperature (OC) in the periods given by D w50% and D w90 %, respectively. 50% and 90% of WmBx (mg kernel-I) W50% and W90%
Carbohydrate Content and Grain Growth
439
For comparison of growth curves from different locations or years it would be better to compute the curve on a sum of temperature scale instead on a time scale (CERNING 1970). This scale is created by continuous addition of the mean daily temperature, as is common in meteorology. The calculated parameters a, b, m, Wo and the above indicated values enable a more precise description of the kernel growth than the primary experimental data. Furthermore, they make it simpler to compare quantitatively the kernel growth and its characteristics of different varieties and under different climatic conditions.
Results
The coefficients a, b, m, and Wo are without any clear physiological meaning. But the parameter m is of special interest because it determines the coordinates of the inflection point of the growth curve. A value of 2 for m indicates that the curve is symmetrical: the x-coordinate for the inflection point and W50% are identical. Values between 1 and 2 indicate that the inflection point is reached before half-saturation. In this growth type more than 50 % of the final dry matter in the kernel is accumulated after having passed the phase of exponential growth. The reverse is indicated by a m value higher than 2. For the analysed cultivars (Table 1) the deviations from 2 for m are not considerable, so that in most cases the growth curves are of quasi-symmetrical shape. Generally there is a tendency to higher values in the winter wheat varieties in comparison with the spring barleys. The highest values were found in the modern high yielding varieties (Kavkas, Charkovska, Mironovskaja 808, Pilot). This means that kernel growth fo these varieties was favoured by a longer lasting phase of exponential growth. However, this hypothesis needs a detailed examination because the W max values for spring barley are not much lower than those for wheat, but the m values differ considerably. The lowest W max is associated with the lowest W'max of the variety Diamant. But this relationship between W max and W'max is not so consistent in varieties with higher W'max. Similarly, no simple explanation for differences in RGR can be found. The KM spring barley has practically the same RGR when grown in Gatersleben or Kromeriz. On the other hand, Kavkas in Gatersleben shows much lower RGR than that in Kromeriz. The data for Dw and Tw may be characterized in the similar way as those for m: there is a clear difference between barley and wheat varieties. Varietal differences and those between two cultivation places will be analysed after the evaluation of further experiments. Examples of the growth curves are presented in Fig. 1. The rate curves of kernel growth and the content of ethanol-soluble substances (e.s.s.) in the culm are given, with both time (1 a, b) and temperature (1 c, d) scales. The curves are comparable for the other varieties studied. The content of ethanol soluble substances changes in the same way as does the kernel growth rate. The maximum of e.s.s. in samples from both Gatersleben and Kromeriz is reached by about one sampling earlier than maximum growth rate. The synchronous time course of the content of e.s.s. and kernel growth rate results in highly significant correlation coefficients (Table 2) calculated from values of kernel
i::i p.
~ ;..l:d
548 670 634 723 614 646 717 723
294 409 423 433 404 428 467 466
35.6 40.3 40.8 42.6 39.2 41.3 44.3 44.2
19.4 25.3 28.5 27.3 27.2 28.6 29.3 29.2
0.079 0.078 0.074 0.082 0.065 0.083 0.082 0.067 0.072
1.93 1.98 1.89 1.98 1.84 2.08 2.15 1.90 1.95
48.76 50.92 51.06 47.08 54.98 48.71 52.04 55.30 54.12
1.037 0.914 1.052 0.728 2.241 0.930 0.725 1.660 0.965
1.903 1.332 1.915 2.407 2.514 2.515 2.291 2.495 2.133
0.170 0.369 0.158 0.134 0.102 0.130 0.139 0.106 0.132
0.0051
0.1001
0.0043
0.0006
0.0002
0.0004
0.0009
0.0003
0.0014
KM (Kr.)
KM(G)
Carola (G)
Kavkas (Kr.)
Kavkas (G)
Charkovska (Kr.)
Mironovskaja 808 (Kr.)
Pilot (G)
Derenburger Silber (G)
>-3
~
~
579
342 37.5 23.4
0.078
1.80
46.28
0.704
1.714
0.187
0.0096
,..tTl
> ."
Ametyst (Kr.)
602 357 39.1
39.85
0.855
1.812
24.5
~
OJ 71
617 350 39.4 24.1
0.074
1.47
0.0086
T w90 % °C TW50% I:d mt
DW90 % d
DW50 % d
RGR d- I
W'max
mg. d- I
W max
mg
Diamant (Kr.)
Coefficients of the growth curves (time scale) Wo m -a b
For explanation, see material and methods. (Kr.) = Kromeriz, (G) = Gatersleben
Table 1. Values characterizing kernel growth of barley and wheat cultiva.rs.
~
~
o
441
Carbohydrate Content and Grain Growth
60
13
10
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10
15
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30
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30
Biochem. Physiol. Pflanzen, Bd. 169
35
50
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442
APEL
and L. NATR
c..J
e oo~ 0
o
I
~o
40
..-:. 0
30 ZO
:g
10
o.
100.
200.
300.
400.
500.
600.
700.
800.
900.
600
700
800
900
1000..( dml °C
1c
50 40 ~ 30
...., 20
g
10
o
100
200
.300
400
500
1000
~
ami DC
ld
Fig. 1. Growth of wheat grains, variety "I{avkas". The sigmoid curve is the computed growth curve, the empirical values are marked by the circles. The time course of the absolute growth rate is represented by the optimum curve as the first derivative of the growth curve (mg. d- 1 ). The content of ethanol soluble substances is represented by the polygon (mg/culm). In la the polygon with the dotted line represents the content of anthron-positive substances (sugars) in the e.s.s. (mg/culm). la and 1c represent the curves from Gaterfileben, lb and ld that from Kromeriz.
Carbohydrate Content and Grain Growth
443
Table 2. Coefficients of correlation, calculated from values of kernel growth rate and the content of e.s.s. as measured at the individual samplings. r 1 : Correlation between growth rate and the content of e.s.s. in % of culm dry weight r 2 : Correlation between kernel growth rate and total e.s.s. (mg) in the culm 0: indicates'that the correlation is not significant at the 5 % level (Kr.) = Kromeriz, (G) = Gatersleben Variety
r1
r2
Barley Ametyst (Kr.) Diamant (Kr.) KM (Kr.) KM(G)
0.850 0.742 0.829 0.946
0.888 0,699 0.763 0.917
Wheat CaroIa (G) Kavkas (Kr.) Kavkas (G) Charkovska (Kr.) Mironovskaja 808 (Kr.) Pilot (G) Derenburger Silber (G)
0.945 0.576° 0.860 0.560° 0.563° 0.885 0.932
0.957 0.580° 0.920 0.565° 0.580° 0.858 0.917
growth rate (W') and the content of e.s.s. as measured at the individual samplings. Here, very large differences between wheat grown in Gatersleben and that in Kromeriz may be seen. The correlation coefficients for wheat from Kromeriz are low and not significant. In this connection, the difference in other characteristics should also be mentioned, e.g. for the variety Kavkas, which was grown both in Gatersleben and in Kromeriz. The mean grain weight at maturity was 55 mg and 47 mg, the grain weight per ear was 2,59 g and 1.51 g, the maximum dry weight of one culm 2.68 g and 1.78 g,. all data given for Gatersleben and Kromeriz, respectively. In the connection with the data, it is not surprising that the content of e.s.s. reached only 602 mg per culm 25 days after anthesis in Kromeriz, but 981 hlg/culm 28 days after anthesis in Gatersleben (Fig.1a and 1b). Discussion
It can be deduced from the morphology of a cereal plant that the stem represents the organ with the largest storage capacity for assimilates. Comparing the maximum content of e.s.s. per culm, i. e. 602 mg in Kromeriz and 981 mg in Gatersleben, with the final grain weight per ear, i. e. 1.51 g and 2.59 g indicates, that at one moment, nearly 40% of the final grain weight (precisely 39.9 % in Kromeriz and 37.8 % in Gatersleben} was present in the stem at the stage when 50 % was already accumulated in the kernels. This comparison clearly indicates the importance of temporary assimilate storage in the culm for grain growth. 30'
444
P.
APEL
and L.
NATR
Fig. 2. Scheme illustrating the relationship between the source of assimilates (1), conductive tissues (2), pool of assimilates (3), kernels (4), a,nd other sinks (5).
Stopping photosynthesis of barley and wheat plants by CO 2-free air for [) days during the grain filling period had no effect on grain growth rate in earlier experiments (NA.TR and APEL 1974; APEL 1974). The continuing kernel growth under conditions of no current photosynthesis was presumably assured with dry matter from the other source, i. e. from reserve assimilates. The amount of substances present in the pool results from the influx of currently produced assimilates and their outflux to various sinks. The scheme (Fig. 2) shows the connections between the compartments participating in tbe assimilate distribution. For this general schema and with regard to the known experimental results, the sinksource relationship during grain filling period may be characterized as follows: As long as the assimilate content in compartment 3 increases synchronously with that in 4 there is no reason to suppose that assimilate production is limiting the grain growth. Hence, growth conditions like temperature ~W ARDLAW 1970), synthetic processes in the grain, content and equilibrium of growth substances (MICHAEL et al. 1970; WHEELER 1972) or transport of assimilates (JENNER and RATHJEN 1972a, b) will determine the kernel growth in the early stages of its development. The assimilate supply for the grain could become the limiting factor when other strong sinks, e. g., rapidly growing stem, growth of newly formed tillers, appeared. But there are no indications that this happens under normal conditions. Whether the supply of assimilates limits the kernel growth in the later stages remains an open question. During the short period of maximum assimilate content, expressed as e.s.s. of the culm, an equilibrium exists between assimilate production and its use in growth. Later, the demand of different sinks including respiration surpasses photosynthetic production and the e.s.s. content in the culm decreases. This again seems to be a clear indication, that the supply could be inadequate at the later stages. However, it cannot be excluded, that some endogenous conditions in the grain and ear themselves induce the cessation of any further development. Similarly, WALPOLE and MORGAN (1970, 1971, 1974) came to the same conclusion for wheat from a different type of investigations. The conclusion that "grain growth is not limited by assimilate supply in the early stages of development but that it could well be in the later stages" seems to be generally acceptable (THORNE 1974).
Carbohydrate Content and Grain Growth
445
References APEL, P., PEISKER, M., Experiments in the regulation of photosynthetic rate with cereals. In: "Breeding and Productivity of Barley". Proc. Int. Symp. 1972 Kromeriz. Kromeriz 1973. TSCHAPE, M., SCHALLDACH, I., AURICH, 0., Die Bedeutung der Karyopsen fiir die Photosynthese und Trockensubstanzproduktion bei Weizen. Photosynthetica 7, 132~139 (1973). Wachstum von Weizenkaryopsen bei versrhiedener CO 2 -Konzentration. Biochem. Physiol. Pflanzen 166, 475~480 (1974). JANK, H.- W., LEHMANN, CHR. 0., Beschreibung des Wachs turns von Weizenkaryopsen mit lIilfe einer Wachstumsfunktion. Archiv f. Ziichtungsforsrhung 6, 181-191 (1975). CERNING, J., Contribution It !'etude de i'evolution de la composition glucidique des ccn3ales au rours de leur maturation: Mais, ble, orge. These de doctorat. Dniversite Lille 1970. JENNER, C. F., RATHJEN, A. J., Factors limiting the supply of sucrose to the developing wheat grain. Ann. Bot. 36, 729~741 (1972 a). ~ ~ Limitations to the accumulation of starch in the developing wheat grain Ann. Bot. 36, 743~ 754 (1972b). KING, R. W., WARDLAW, 1. F., EVANS, L. T., Effect of assimilate utilization on photosynthetic rate in wheat. Planta 77, 261~276 (1967). LUPTON, F. G. H., The analysis of grain yield of wheat in terms of photosynthetic ability and efficiency of translocation. Ann. appl. BioI. 61, 109 ~ 119 (1968). MCCREADY, R. M., GUGGOLZ, J., SILVIERA, V., OWENS, H. S., Determination of starch and amylose in vegetables. Analyt. Chemistry 22 1156~1158 (1950). MICHAEL, G., ALLINGER, P., WILBERG, E., Einige Aspekte zur hormonalen Regulation der KorngriiBe bei Getreide. Z. Pflanzenerniihrung und Bodenkunde 126, 24~35 (1970). NATR, L., APEL, P., The influence of the rate of photosynthate production on the rate of dry matter accumulation in barley kernels. Photosynthetica 8, 53~56 (1974). NOSBERGER, J., THORNE, G. N., The effect of removing florets or shading the ear of barley on production and distribution of dry matter. Ann. Bot. 29, 635~644 (1965). RICHARDS, F. J., A flexible growth function for empirical use. J. Exptl. Botany 10, 290~300 (1959). The quantitative analysis of growth. In: Plant Physiology Vol. VA: Analysis of Growth: Behaviour of Plant and Their Organs (Ed. F. C. STEWARD). pp. 3~77. Acad. Press, New York and London 1969. SL USARCZYK, M., WOJCIESKA, D., Distribution of photosynthates and carbohydrate metabolism in the culms of wheat. Bull. de i'Acad. Polon. des Sciences, Ser. des Sciences BioI. Cl. V, 22, 617~623 (1974). SPJERTZ, J. H. J., Grain growth and distribution of dry matter in the wheat plant as influenced by temperature, light energy and ear size. Netherl. J. agric. Sci. 22, 207 ~220 (1974). THORNE, G. N., The source ~ sink concept in relation to productivity of cereals. In: "Breeding and Productivity of Barley". Proc. Int. Symp. 1972 Kromeriz. Kromeriz 1973. ~ Physiology in grain yield of wheat and barley. In: Rothamsted Expt. Station. Report for 1973, Part 2, pp. 5~25 (1974). WALPOLE, P. R., MORGAN, D. G., A quantitative study of grain filling in Triticum aestivum L., cultivar Maris Widgeon. Ann. Bot. 34, 309~318 (1970). ~ A quantitative study of grain filling in three cultivars of Hordeum vulgare. L. Ann. Bot. 36, 301~310 (1971). ~ The influence of leaf removal upon the development of the grain of winter wheat. Ann. Bot. 38, 779~782 (1974).
II
I
! '
,
'
i
ii •
i,
446
P. APEL and L. NATR, Carbohydrate Content and Grain Growth
WARDLAW, I. F., The early stages of grain development in wheat: Response to light and temperature in a single variety. Aust. J. bioI. Sci. 23,765-774 (1970). WHEELER, A. W., Changes in growth-substance contents during growth of wheat grains. Ann appi. BioI. 72, 327 - 334 (1972). YOSHIDA, SH., Physiological aspects of grain yield. Annu. Rev. Plant Physioi. 23, 437 -464 (1972). Received October 28, 1975. Authors' address: Dr. P. APEL, Zentralinstitut fiir Genetik und Kulturpflanzenforschung, 4325 Gatersleben and L. Natr, Institute of Cereal Crops, Kromeriz, CSSR.
Biochem. Physiol. Pflanzen 169, S. 437 -446 (1976)
Carbohydrate Content and Grai·n Growth in Wheat and Barley P. APEL and L. NATR Zentralinstitut fiir Genetik und Kulturpflanzenforschung der AdW, Gatersleben and Institute of Cereal Crops, Kromeriz, CSSR Key Term Index: assimilate storage, grain growth, sink-source relation; Hordeum spec., Triticum spec.
Summary The time course of grain growth and the content of ethanol soluble substances in the culm in spring barley, spring wheat and winter wheat were investigated. The maximum value of sugars in the culm was reached about 5 days before the maximum of the growth rate of kernels. From the results it was concluded that temporary storage of assimilates in the culm assures optimum grain growth also under unfavourable conditions for photosynthesis. Under the given experimental conditions grain growth was not limited by assimilate supply in the early stages of development.
Introduction
The dry matter accumulated in cereal grains comprises hoth the assimilates currently produced in the photosynthesizing organs and assimilates temporarily stored. The storage capacity for photosynthetic products of stem and also leaf tissue is fairly high (YOSHIDA 1972; APEL et al. 1973; SLUSARCZYK and WOJCIESKA 1974; SPIERTZ 1974). This may be deduced from the fact that shortly after anthesis the assimilate production is very high and kernel growth, i. a., rate of dry matter accumulation in the kernels is negligible. Some contrary results published in the last decade may be understood as special cases of the relationship between assimilate production, temporary storage and demand of assimilates for grain growth and respiration. For example, the correlation between the demand of assimilates in the ear and the rate of flag leaf photosynthesis (KING et al. 1967) could indicate that under the given experimental conditions the capacity of the plants for temporary assimilate storage was fully saturated. On the other hand, the non-existence of any dependence of leaf photosynthesis on the assimilate demand in sink organs (NOSBERGER and THORNE 1965; LUPTON 1968; THORNE 1972; APEL and PEISKER 1972; APEL et al. 1973) indicates that there is no control over photosynthesis by the non-saturated pool of assimilates. Therefore one could expect a wide range of relationships between sink and source depending on growth conditions before grain development and on varietal characters. The quantitative description of the course of the grain growth and its comparison with changes in the amount of soluble substances in the stem as presented in this paper attempt to provide basic information necessary for further investigation.
I
II,
III
438
P. APEL and L. N1.TR
Material and Methods Material. - Spring barley: Diamant, Ametyst, KM 1192. Diamant and Ametyst are varieties from the CSSR, KM is a breeding line from CSSR. - Spring wheat: Carola. This variety was bred in GDR anll successful in the sixties. - Winter wheat: Kavkas, Charkovska, Mironovskaja 808, Pilot, Derenburger Silber. Kavkas, Charkovska and Mironovskaja 808 are modern varieties from Soviet Union, Pilot is a modern and Derenburger Silber an old variety from GDR. The varieties were grown 1974 in the experimental fields at Kromeriz and Gatersleben, only Kavkas and KM in both locations. (Kromeriz: 48°18' degrees of latitude, 17°23' degrees of longitude; height above sea level 204 m; average year precipitation 599 mm; average day temperature 8,6 °C, Gatersleben: 51°49' degrees of latitude, 11°17' degrees of longitude; height above sea level 110 m, average year precipitation 492 mm; average day temperature 8,4 °C.) During anthesis about 200 culms bearing ears of the same developmental stage were marked. On the 10th day after anthesis the first sample of 15 culms was harvested. Further samples were taken in regular intervals of 5 days till full maturity. The culms of each harvest were divided into grains (by dissecting them out from the ears) into leaves (blades and sheath) and culms. The fractions were dried at 110°C during the first two h and at 65°C during the following two days and finally their dry weight was determined. Analysis. - The pulverized material of the culms was subsequently extracted three times with hot 80 % ethanol. The amount of ethanol soluble substances (e.s.s.) was calculated as the difference between the culm dry weight before and after extraction. In some cases sugar and starch content was determined using a modified procedure of MCCREADY et al. (1950). Mathematical description of grain grwoth. - For mathematical description of the kernel dry weight changes from anthesis to maturity Richards' comprehensive growth function was used (RICHARDS 1959, 1969). Here, the growth rate is given by dW -=a·Wm+b·W
dt
W = dry weigth, a, b, and m are parameters. The integral of this function is 1
W,t) = [ (ila + Wol-m ) • eb . t· (l-m) _ila]l-m Wo is the dry weight at zero time. The parameters a, b, m, and Wo were computed from the empirical data by a least square method (APEL et al. in press). From the function the time course of absolute and relative growth rates was calculated as well as the following values: computed saturation level for the kernel growth curve. W max is nearly identical with the WmBX mean of empirical values of the last two or three samplings. maximum of the first derivative of the growth curve (mg. grain-I. d- l ). This value W'max indicates maximum growth rate of the grains. average relative growth rate for the time between 10 % and 90 % dry weight using the formula: (In W90% - In W10%) t90% - t 10% Dw50% and D w90 % - number of days from anthesis till the time when grain dry weight reaches 50 % and 90 % of its final weight, respectively. T w50% and T w90% the sum of daily mean temperature (OC) in the periods given by D w50% and D w90 %, respectively. 50% and 90% of WmBx (mg kernel-I) W50% and W90%
Carbohydrate Content and Grain Growth
439
For comparison of growth curves from different locations or years it would be better to compute the curve on a sum of temperature scale instead on a time scale (CERNING 1970). This scale is created by continuous addition of the mean daily temperature, as is common in meteorology. The calculated parameters a, b, m, Wo and the above indicated values enable a more precise description of the kernel growth than the primary experimental data. Furthermore, they make it simpler to compare quantitatively the kernel growth and its characteristics of different varieties and under different climatic conditions.
Results
The coefficients a, b, m, and Wo are without any clear physiological meaning. But the parameter m is of special interest because it determines the coordinates of the inflection point of the growth curve. A value of 2 for m indicates that the curve is symmetrical: the x-coordinate for the inflection point and W50% are identical. Values between 1 and 2 indicate that the inflection point is reached before half-saturation. In this growth type more than 50 % of the final dry matter in the kernel is accumulated after having passed the phase of exponential growth. The reverse is indicated by a m value higher than 2. For the analysed cultivars (Table 1) the deviations from 2 for m are not considerable, so that in most cases the growth curves are of quasi-symmetrical shape. Generally there is a tendency to higher values in the winter wheat varieties in comparison with the spring barleys. The highest values were found in the modern high yielding varieties (Kavkas, Charkovska, Mironovskaja 808, Pilot). This means that kernel growth fo these varieties was favoured by a longer lasting phase of exponential growth. However, this hypothesis needs a detailed examination because the W max values for spring barley are not much lower than those for wheat, but the m values differ considerably. The lowest W max is associated with the lowest W'max of the variety Diamant. But this relationship between W max and W'max is not so consistent in varieties with higher W'max. Similarly, no simple explanation for differences in RGR can be found. The KM spring barley has practically the same RGR when grown in Gatersleben or Kromeriz. On the other hand, Kavkas in Gatersleben shows much lower RGR than that in Kromeriz. The data for Dw and Tw may be characterized in the similar way as those for m: there is a clear difference between barley and wheat varieties. Varietal differences and those between two cultivation places will be analysed after the evaluation of further experiments. Examples of the growth curves are presented in Fig. 1. The rate curves of kernel growth and the content of ethanol-soluble substances (e.s.s.) in the culm are given, with both time (1 a, b) and temperature (1 c, d) scales. The curves are comparable for the other varieties studied. The content of ethanol soluble substances changes in the same way as does the kernel growth rate. The maximum of e.s.s. in samples from both Gatersleben and Kromeriz is reached by about one sampling earlier than maximum growth rate. The synchronous time course of the content of e.s.s. and kernel growth rate results in highly significant correlation coefficients (Table 2) calculated from values of kernel
i::i p.
~ ;..l:d
548 670 634 723 614 646 717 723
294 409 423 433 404 428 467 466
35.6 40.3 40.8 42.6 39.2 41.3 44.3 44.2
19.4 25.3 28.5 27.3 27.2 28.6 29.3 29.2
0.079 0.078 0.074 0.082 0.065 0.083 0.082 0.067 0.072
1.93 1.98 1.89 1.98 1.84 2.08 2.15 1.90 1.95
48.76 50.92 51.06 47.08 54.98 48.71 52.04 55.30 54.12
1.037 0.914 1.052 0.728 2.241 0.930 0.725 1.660 0.965
1.903 1.332 1.915 2.407 2.514 2.515 2.291 2.495 2.133
0.170 0.369 0.158 0.134 0.102 0.130 0.139 0.106 0.132
0.0051
0.1001
0.0043
0.0006
0.0002
0.0004
0.0009
0.0003
0.0014
KM (Kr.)
KM(G)
Carola (G)
Kavkas (Kr.)
Kavkas (G)
Charkovska (Kr.)
Mironovskaja 808 (Kr.)
Pilot (G)
Derenburger Silber (G)
>-3
~
~
579
342 37.5 23.4
0.078
1.80
46.28
0.704
1.714
0.187
0.0096
,..tTl
> ."
Ametyst (Kr.)
602 357 39.1
39.85
0.855
1.812
24.5
~
OJ 71
617 350 39.4 24.1
0.074
1.47
0.0086
T w90 % °C TW50% I:d mt
DW90 % d
DW50 % d
RGR d- I
W'max
mg. d- I
W max
mg
Diamant (Kr.)
Coefficients of the growth curves (time scale) Wo m -a b
For explanation, see material and methods. (Kr.) = Kromeriz, (G) = Gatersleben
Table 1. Values characterizing kernel growth of barley and wheat cultiva.rs.
~
~
o
441
Carbohydrate Content and Grain Growth
60
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10
15
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30
Biochem. Physiol. Pflanzen, Bd. 169
35
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P.
442
APEL
and L. NATR
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e oo~ 0
o
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~o
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..-:. 0
30 ZO
:g
10
o.
100.
200.
300.
400.
500.
600.
700.
800.
900.
600
700
800
900
1000..( dml °C
1c
50 40 ~ 30
...., 20
g
10
o
100
200
.300
400
500
1000
~
ami DC
ld
Fig. 1. Growth of wheat grains, variety "I{avkas". The sigmoid curve is the computed growth curve, the empirical values are marked by the circles. The time course of the absolute growth rate is represented by the optimum curve as the first derivative of the growth curve (mg. d- 1 ). The content of ethanol soluble substances is represented by the polygon (mg/culm). In la the polygon with the dotted line represents the content of anthron-positive substances (sugars) in the e.s.s. (mg/culm). la and 1c represent the curves from Gaterfileben, lb and ld that from Kromeriz.
Carbohydrate Content and Grain Growth
443
Table 2. Coefficients of correlation, calculated from values of kernel growth rate and the content of e.s.s. as measured at the individual samplings. r 1 : Correlation between growth rate and the content of e.s.s. in % of culm dry weight r 2 : Correlation between kernel growth rate and total e.s.s. (mg) in the culm 0: indicates'that the correlation is not significant at the 5 % level (Kr.) = Kromeriz, (G) = Gatersleben Variety
r1
r2
Barley Ametyst (Kr.) Diamant (Kr.) KM (Kr.) KM(G)
0.850 0.742 0.829 0.946
0.888 0,699 0.763 0.917
Wheat CaroIa (G) Kavkas (Kr.) Kavkas (G) Charkovska (Kr.) Mironovskaja 808 (Kr.) Pilot (G) Derenburger Silber (G)
0.945 0.576° 0.860 0.560° 0.563° 0.885 0.932
0.957 0.580° 0.920 0.565° 0.580° 0.858 0.917
growth rate (W') and the content of e.s.s. as measured at the individual samplings. Here, very large differences between wheat grown in Gatersleben and that in Kromeriz may be seen. The correlation coefficients for wheat from Kromeriz are low and not significant. In this connection, the difference in other characteristics should also be mentioned, e.g. for the variety Kavkas, which was grown both in Gatersleben and in Kromeriz. The mean grain weight at maturity was 55 mg and 47 mg, the grain weight per ear was 2,59 g and 1.51 g, the maximum dry weight of one culm 2.68 g and 1.78 g,. all data given for Gatersleben and Kromeriz, respectively. In the connection with the data, it is not surprising that the content of e.s.s. reached only 602 mg per culm 25 days after anthesis in Kromeriz, but 981 hlg/culm 28 days after anthesis in Gatersleben (Fig.1a and 1b). Discussion
It can be deduced from the morphology of a cereal plant that the stem represents the organ with the largest storage capacity for assimilates. Comparing the maximum content of e.s.s. per culm, i. e. 602 mg in Kromeriz and 981 mg in Gatersleben, with the final grain weight per ear, i. e. 1.51 g and 2.59 g indicates, that at one moment, nearly 40% of the final grain weight (precisely 39.9 % in Kromeriz and 37.8 % in Gatersleben} was present in the stem at the stage when 50 % was already accumulated in the kernels. This comparison clearly indicates the importance of temporary assimilate storage in the culm for grain growth. 30'
444
P.
APEL
and L.
NATR
Fig. 2. Scheme illustrating the relationship between the source of assimilates (1), conductive tissues (2), pool of assimilates (3), kernels (4), a,nd other sinks (5).
Stopping photosynthesis of barley and wheat plants by CO 2-free air for [) days during the grain filling period had no effect on grain growth rate in earlier experiments (NA.TR and APEL 1974; APEL 1974). The continuing kernel growth under conditions of no current photosynthesis was presumably assured with dry matter from the other source, i. e. from reserve assimilates. The amount of substances present in the pool results from the influx of currently produced assimilates and their outflux to various sinks. The scheme (Fig. 2) shows the connections between the compartments participating in tbe assimilate distribution. For this general schema and with regard to the known experimental results, the sinksource relationship during grain filling period may be characterized as follows: As long as the assimilate content in compartment 3 increases synchronously with that in 4 there is no reason to suppose that assimilate production is limiting the grain growth. Hence, growth conditions like temperature ~W ARDLAW 1970), synthetic processes in the grain, content and equilibrium of growth substances (MICHAEL et al. 1970; WHEELER 1972) or transport of assimilates (JENNER and RATHJEN 1972a, b) will determine the kernel growth in the early stages of its development. The assimilate supply for the grain could become the limiting factor when other strong sinks, e. g., rapidly growing stem, growth of newly formed tillers, appeared. But there are no indications that this happens under normal conditions. Whether the supply of assimilates limits the kernel growth in the later stages remains an open question. During the short period of maximum assimilate content, expressed as e.s.s. of the culm, an equilibrium exists between assimilate production and its use in growth. Later, the demand of different sinks including respiration surpasses photosynthetic production and the e.s.s. content in the culm decreases. This again seems to be a clear indication, that the supply could be inadequate at the later stages. However, it cannot be excluded, that some endogenous conditions in the grain and ear themselves induce the cessation of any further development. Similarly, WALPOLE and MORGAN (1970, 1971, 1974) came to the same conclusion for wheat from a different type of investigations. The conclusion that "grain growth is not limited by assimilate supply in the early stages of development but that it could well be in the later stages" seems to be generally acceptable (THORNE 1974).
Carbohydrate Content and Grain Growth
445
References APEL, P., PEISKER, M., Experiments in the regulation of photosynthetic rate with cereals. In: "Breeding and Productivity of Barley". Proc. Int. Symp. 1972 Kromeriz. Kromeriz 1973. TSCHAPE, M., SCHALLDACH, I., AURICH, 0., Die Bedeutung der Karyopsen fiir die Photosynthese und Trockensubstanzproduktion bei Weizen. Photosynthetica 7, 132~139 (1973). Wachstum von Weizenkaryopsen bei versrhiedener CO 2 -Konzentration. Biochem. Physiol. Pflanzen 166, 475~480 (1974). JANK, H.- W., LEHMANN, CHR. 0., Beschreibung des Wachs turns von Weizenkaryopsen mit lIilfe einer Wachstumsfunktion. Archiv f. Ziichtungsforsrhung 6, 181-191 (1975). CERNING, J., Contribution It !'etude de i'evolution de la composition glucidique des ccn3ales au rours de leur maturation: Mais, ble, orge. These de doctorat. Dniversite Lille 1970. JENNER, C. F., RATHJEN, A. J., Factors limiting the supply of sucrose to the developing wheat grain. Ann. Bot. 36, 729~741 (1972 a). ~ ~ Limitations to the accumulation of starch in the developing wheat grain Ann. Bot. 36, 743~ 754 (1972b). KING, R. W., WARDLAW, 1. F., EVANS, L. T., Effect of assimilate utilization on photosynthetic rate in wheat. Planta 77, 261~276 (1967). LUPTON, F. G. H., The analysis of grain yield of wheat in terms of photosynthetic ability and efficiency of translocation. Ann. appl. BioI. 61, 109 ~ 119 (1968). MCCREADY, R. M., GUGGOLZ, J., SILVIERA, V., OWENS, H. S., Determination of starch and amylose in vegetables. Analyt. Chemistry 22 1156~1158 (1950). MICHAEL, G., ALLINGER, P., WILBERG, E., Einige Aspekte zur hormonalen Regulation der KorngriiBe bei Getreide. Z. Pflanzenerniihrung und Bodenkunde 126, 24~35 (1970). NATR, L., APEL, P., The influence of the rate of photosynthate production on the rate of dry matter accumulation in barley kernels. Photosynthetica 8, 53~56 (1974). NOSBERGER, J., THORNE, G. N., The effect of removing florets or shading the ear of barley on production and distribution of dry matter. Ann. Bot. 29, 635~644 (1965). RICHARDS, F. J., A flexible growth function for empirical use. J. Exptl. Botany 10, 290~300 (1959). The quantitative analysis of growth. In: Plant Physiology Vol. VA: Analysis of Growth: Behaviour of Plant and Their Organs (Ed. F. C. STEWARD). pp. 3~77. Acad. Press, New York and London 1969. SL USARCZYK, M., WOJCIESKA, D., Distribution of photosynthates and carbohydrate metabolism in the culms of wheat. Bull. de i'Acad. Polon. des Sciences, Ser. des Sciences BioI. Cl. V, 22, 617~623 (1974). SPJERTZ, J. H. J., Grain growth and distribution of dry matter in the wheat plant as influenced by temperature, light energy and ear size. Netherl. J. agric. Sci. 22, 207 ~220 (1974). THORNE, G. N., The source ~ sink concept in relation to productivity of cereals. In: "Breeding and Productivity of Barley". Proc. Int. Symp. 1972 Kromeriz. Kromeriz 1973. ~ Physiology in grain yield of wheat and barley. In: Rothamsted Expt. Station. Report for 1973, Part 2, pp. 5~25 (1974). WALPOLE, P. R., MORGAN, D. G., A quantitative study of grain filling in Triticum aestivum L., cultivar Maris Widgeon. Ann. Bot. 34, 309~318 (1970). ~ A quantitative study of grain filling in three cultivars of Hordeum vulgare. L. Ann. Bot. 36, 301~310 (1971). ~ The influence of leaf removal upon the development of the grain of winter wheat. Ann. Bot. 38, 779~782 (1974).
II
I
! '
,
'
i
ii •
i,
446
P. APEL and L. NATR, Carbohydrate Content and Grain Growth
WARDLAW, I. F., The early stages of grain development in wheat: Response to light and temperature in a single variety. Aust. J. bioI. Sci. 23,765-774 (1970). WHEELER, A. W., Changes in growth-substance contents during growth of wheat grains. Ann appi. BioI. 72, 327 - 334 (1972). YOSHIDA, SH., Physiological aspects of grain yield. Annu. Rev. Plant Physioi. 23, 437 -464 (1972). Received October 28, 1975. Authors' address: Dr. P. APEL, Zentralinstitut fiir Genetik und Kulturpflanzenforschung, 4325 Gatersleben and L. Natr, Institute of Cereal Crops, Kromeriz, CSSR.