time between anthesis estimated from the sam- pling date when plants were producing new flow-
ers and 95 of final oil content ranged from 37 to 49 days Table 1.
3
.
4
. Variation in oil and g-linolenic acid contents in seeds from different parts of the plant
In all cv. Merlin treatments, most seed was produced on the main stems Table 2. In years 1
and 2, the main stem seeds contained a higher percentage of oil than seeds from the upper pri-
mary branches, but in year 3 the differences in oil content were not significant. Seeds from the upper
primary branches had the lowest TSW, but g-lino- lenic contents were similar throughout the plant.
In cv. Peter the upper primary branches con- tributed 76 of total seed yield and this seed
contained significantly more oil than did seeds from the main stems or basal primary branches.
For the year one spring crop, seed samples from earlier brown and later green ripening
capsules were analysed. A capsule was counted as brown if at least half of its length was brown.
Seeds from the early maturing main stem capsules contained 16 more oil than seeds from the later
capsules Table 3. The differences in oil content between the earlier and later maturing seeds on
the primary branches were not significant. Simi- larly, there were no significant differences in seed
size between early and later maturing seeds on a stem. The oil in the seeds from the later maturing
capsules tended to have the highest g-linolenic acid content, but the difference was only signifi-
cant P, 0.052 for the upper primary branches.
4. Discussion
Our results show that oil and g-linolenic acid content of evening primrose seeds can be strongly
influenced by the climatic conditions prevailing during seed growth, such that on occasions the
quality of the harvested seed is below that accept- able to the market. Seeds from overwintered crops
tended to contain more oil, but with a lower
g -linolenic acid content, than seeds from spring-
sown crops Table 1. The use of improved culti- vars such as cv. Merlin can reduce the risk of
producing low-quality seed but, even for a given cultivar and time of sowing, large differences in
oil and g-linolenic acid content can occur between years.
Fig. 4. The relationship in evening primrose cv. Merlin be- tween a final oil content of the seeds and mean daily temper-
ature during the period from 5 to 95 of final oil content, b final oil content of the seeds and mean daily incident photo-
synthetically-active radiation during the period from 5 to 80 of final oil content and c final g-linolenic acid GLA content
of the oil and mean daily temperature during the period from 85 to 95 of final oil content of the seeds. Oil and g-linolenic
acid contents were estimated from Gompertz growth model functions. Closed symbols, overwintered crops; open symbols:
spring crops; circles, year 1; squares, year 2; triangles, year 3.
A .F
. Fieldsend
, J
.I .L
. Morison
Industrial Crops
and Products
12 2000
137 –
147
Table 2 Distribution of yield, mean oil content of seeds, g-linolenic acid content C18:3v6 of seed oil and thousand seed weight TSW of seeds from evening primrose plants harvested at growth
stage G.S. 5,95 in 3 years
a
Year 3
b
Year 2
b
Seed source
a
Year 1
b
Oil C18:3v6
TSW g of yield
Oil C18:3v6
of yield TSW g
of yield TSW g
C18:3v6 Oil
68 79
28.1a 8.70a
0.358a 94
26.3a 9.03a
0.348a 25.0a
8.09a 0.360a
WM-M 27.3a
8.70a 0.350a
21 24.7a
B 9
0.323a 8.41a
11 12
27.3a 8.62a
0.293b 6
26.5a 8.99a
0.301b 21.5b
7.46b 0.323a
U 0.458
0.139 0.019
0.504 0.119
0.016 1.166
0.257 0.018
SED 0.194
0.797 0.026
0.692 0.789
0.011 0.027
0.044 0.130
P-value 22
24.0a 7.95a
0.468a WP-M
23.0a 8.26a
0.413a B
2 25.5b
7.58a 0.396a
76 U
0.497 0.294
0.032 SED
0.007 0.147
0.146 P-value
24.7a 9.54a
0.339a 65
27.5a 0.386a
8.88a SM-M
0.387a 94
9.41a 23.6a
54 32
23 26.5a
9.34a 0.367ab
22.4b 9.38a
B 0.375a
23.2b 9.52a
0.316a 11
25.9a 9.24a
U 0.320b
14 21.6b
9.46a 0.340b
6 0.279
0.105 0.039
0.647 0.010
0.155 0.020
SED 0.085
0.386 0.013
0.843 0.356
0.117 0.056
0.043 0.005
0.640 0.011
P-value LM-M
72 23.1a
9.85a 0.313a
14 23.9a
10.19b 0.266a
B 14
22.2a 10.27b
0.241a U
SED 0.958
0.100 0.023
0.305 0.012
0.052 P-value
a
Seed source: WM = overwintered cv. Merlin; WP = overwintered cv. Peter; SM = spring-sown cv. Merlin; LM = late spring-sown cv. Merlin; M = main stem; B = basal primary branch; U = upper primary branch.
b
Data bearing the same letters within a column and year are not significantly different at P, 0.05. SED is the standard error of the difference between means for a one-way ANOVA for each year.
Table 3 Mean oil content of seeds, g-linolenic acid C18:3v6 content of oil and thousand seed weight TSW of seeds from earlier brown
and later green ripening capsules from year one spring-sown plants of evening primrose cv. Merlin harvested at G.S. 5,95
a
Oil Stem type
C18:3v6 Capsule colour
TSW g Main
Brown 24.90a
9.33a 0.390a
21.45b 9.54a
Green 0.380a
SED 0.692
0.134 0.012
P-value 0.016
0.211 0.459
22.72a Basal primary branches
9.35a Brown
0.380a Green
22.04a 9.37a
0.371a 0.866
SED 0.107
0.006 0.493
0.864 0.212
P-value Upper primary branches
Brown 21.28a
9.09a 0.318a
21.53a Green
9.57a 0.353a
0.760 SED
0.155 0.031
0.761 0.052
P-value 0.341
a
Data bearing the same letters within a column and year are not significantly different at P, 0.05. SED is the standard error of the difference between means for a one-way ANOVA for each year.
The lipid fraction in newly-formed evening primrose seeds contains a relatively high percent-
age of a-linolenic acid Fig. 1. This percentage declines as the percentage of g-linolenic acid in-
creases, and it has been suggested that during seed maturation a-linolenic acid is transformed into
g -linolenic acid work cited by Cisowski et al.,
1993. This is unlikely, as no pathway for the conversion of a-linolenic acid to g-linolenic acid
has been shown to occur in plants. In fact, ex- pressed as a percentage of seed weight, the
amount of a-linolenic acid present is always low Fig. 2. More probably, at the onset of seed
filling, the concentration of cell membrane lipids in the analysed seed sample was high relative to
the concentration of triacylglycerols, the storage lipids. Furthermore, the proportion of cell mem-
brane lipids in our analysed seed samples will have declined as storage lipids accumulated.
Mukherjee and Kiewitt 1987 demonstrated that
a -linolenic acid is channelled almost exclusively
into phospholipids and glycolipids, which are the major constituents of cellular membranes, but
that the a-linolenic acid content of these lipid classes declines sharply with seed maturation. In
evening primrose seeds g-linolenic acid is incorpo- rated mainly into triacylglycerols.
When comparing analyses of seed oils from plants growing in the wild at different geographi-
cal locations e.g. Lotti et al., 1978, it is very difficult to separate temperature effects from
those of daylength, PAR, soil type and other biotic influences. Interpretation of results from a
single location andor relatively stress-free envi- ronments, such as field crops, can be easier, but
temperature and PAR effects remain difficult to separate. Our data showed a positive relationship
between final seed oil content in evening primrose and mean daily temperature during seed filling
Fig. 4a. The existence of such a relationship would be explained if the synthesis of energy-rich
lipids was favoured over other biochemical pro- cesses by higher, but not extreme, temperatures.
Alternatively, it may be that the amount of inci- dent PAR during oil accumulation particularly
the period of rapid, almost linear increase in oil content, rather than temperature, is the major
determinant of final seed oil content. The basis of such a relationship could be simple: higher inci-
dent PAR should result in more assimilate being available to be partitioned into storage com-
pounds, i.e. oil. If this is the case, it might be expected that the seeds would be larger and a
positive correlation between oil content and TSW
should be demonstrable. Our data do not show such a relationship.
Evening primrose seed oil attains virtually its final percentage content of g-linolenic acid rela-
tively quickly Fig. 1 and it is surprising, there- fore, that temperatures during the earlier part of
the seed filling period appear to have little influ- ence on the final g-linolenic acid content of the
oil. In a growth cabinet study, Levy et al. 1993 showed that final g-linolenic acid percent-
age was most influenced by temperatures 30 – 40 days after anthesis. Similarly, we have shown
that, in the field, temperatures during a 8 – 15 day period ending between 37 and 49 days after
anthesis, as the rate of increase in oil content was slowing down, most strongly determined the
final g-linolenic acid content of the oil. During rapid oil accumulation, the large amount of
linoleic acid produced Fig. 2 may mask any residual effect of temperatures during this period
on the g-linolenic acid content of the oil. Only once the rate of accumulation has slowed might
any temperature effects be detectable subse- quently.
Seeds formed on the main stem of evening primrose cv. Merlin had a higher oil content
and were larger than seeds formed on the branches,
particularly the
upper primary
branches. Similarly, on a main stem, at least, the earlier formed seeds tended have a higher oil
content whereas the later formed seeds on a branch tended to have a higher g-linolenic acid
content in the oil. These results agree with those of Court et al., 1993. However, these differ-
ences may reflect the position of the seed on the plant in relation to supply of assimilate as well
as any influence of climate. In any case, in a commercial situation the range of oil and g-lino-
lenic acid contents present within a seed stock will be reduced by the cleaning process as small
seeds from the later-formed capsules are re- moved Simpson and Fieldsend, 1993.
5. Conclusion
