3. Results
3
.
1
. Effects on 6egetati6e growth The vegetative and reproductive growth of A.
thaliana plant was separated. Prior to bolting, an A. thaliana plant consisted of a rosette of small
leaves with a main hypocotyl. In the present study, results showed that additions of 0.5 – 50 mM
cerium or lanthanum had no significant effects on the vegetative growth in terms of height and dry
weight. Cerium and lanthanum also had no sig- nificant effect on the average number of rosette
leaves 17 days after seed germination data not shown. Additions of higher concentrations of
cerium or lanthanum inhibited the vegetative growth data not shown.
3
.
2
. Effects on root growth A. thaliana plants were observed to produce
only primary roots 10 days after seed germina- tion. In REE-free medium, the length of primary
roots was about 2.0 cm. Addition of 0.5 – 10.0 mM cerium nitrate to the culture medium significantly
increased the lengths of primary roots with longest root 2.84 cm observed in the medium
containing 10.0 mM cerium nitrate Table 1. Sim- ilarly, addition of lanthanum 0.5 – 50.0 mM
singly or in combination with cerium nitrate sig- nificantly increased the lengths of roots Table 1.
3
.
3
. Effects on floral initiation In basal medium, the first appearance of bolting
8.9 was observed on day 20. About 39.4 of the plants bolted on day 23 and by day 27 more
than 98 of the plants bolted Table 2. Addi- tions of cerium nitrate or lanthanum nitrate 0.5 –
2.5 mM significantly increased the percentages of plants bolted on days 20 and 23. For example,
69.3 of the plants growing in the medium with 2.5 mM cerium nitrate bolted on day 23 whereas
only 39.4 bolted in basal medium. About 65.7 of the plants in the medium containing 0.5 mM
lanthanum nitrate bolted on day 23 Table 2. The percentages of plants bolted on day 27 were
not significantly different between media with or without cerium nitrate or lanthanum nitrate
Table 2.
None of the plants growing in basal medium bolted on day 19. Additions of certain combina-
tions of cerium nitrate and lanthanum nitrate e.g. 0.5 + 0.5 mM, 0.5 + 1.0 mM, 1.0 + 0.5 mM, 1.0 +
1.0 mM resulted in early flowering; 4.6 – 8.3 of the plants bolted as early as day 19. The combina-
tion of 0.5 mM cerium nitrate and 0.5 mM lan- thanum nitrate was most effective in induction of
flowering. Nearly 90 of the plants bolted on day 23 in the medium containing 0.5 mM cerium ni-
trate and 0.5 mM lanthanum nitrate compared to only 39.4 bolted in the basal medium. On day
27, no significant difference in the percentage of plants bolted was observed in the media with or
without REE Table 2.
In order to assess the effects of additional ni- trates from lanthanum nitrate and cerium nitrate
on floral initiation, we replaced these two chemi- cals with potassium nitrate. The effects of addi-
tional nitrates 0.3 or 1.0 of the total nitrate level in the 14 strength MS medium on floral
initiation were investigated. The percentages of plants bolted in the media supplemented with the
additional nitrate were not significantly different from those in the basal medium data not shown.
Thus any effects of cerium nitrate and lanthanum
Table 1 Effects of cerium nitrate and lanthanum nitrate on the growth of primary root of A. thaliana 10 days after seed germination
Average root length cm
a
Concentration mM Cerium nitrate
Lanthanum nitrate Cerium nitrate and lanthanum nitrate
1.96 9 0.04a 2.04 9 0.06a
2.04 9 0.06a 0.0
0.5 2.62 9 0.05b
2.58 9 0.04c 2.65 9 0.03b
2.65 9 0.04c 2.58 9 0.04b
2.63 9 0.04b 1.0
10.0 2.54 9 0.05b
2.47 9 0.05b 2.84 9 0.04c
1.81 9 0.03c 2.40 9 0.04b
1.92 9 0.04a 50.0
a
Values were expressed as mean 9 SE. There were 81–95 plants per treatment. Means within the same column followed by the same letter were not significantly different according to Tukey’s pairwise comparisons P = 0.05.
Table 2 Effects of cerium orand lanthanum on floral initiation of A. thaliana
Lanthanum nitrate mM Cerium nitrate mM
Percentage of plants bolted
a
Days after seed germination 19
20 23
27 0.0
8.9 9 3.2 0.0
39.4 9 7.9 0.0
97.7 9 1.4 0.0
14.5 9 2.5 59.4 9 9.9
0.5 96.4 9 1.0
2.5 0.0
17.4 9 3.7 69.3 9 10.4
95.1 9 1.1 0.0
4.3 9 1.9 51.2 9 5.3
10.0 97.7 9 0.7
0.0 0.0
100.0 20.5 9 2.7
94.9 9 1.5 0.0
15.6 9 2.6 0.5
65.7 9 7.8 96.4 9 0.9
2.5 0.0
13.3 9 1.1 62.3 9 5.4
98.7 9 1.9 0.0
7.4 9 1.7 10.0
57.8 9 5.5 94.9 9 2.0
100.0 0.0
0.0 25.7 9 4.2
95.1 9 2.2 0.0
0.1 12.9 9 2.2
0.1 61.1 9 7.1
94.9 9 2.7 0.0
20.2 9 3.2 0.1
80.1 9 9.7 0.5
96.7 9 2.1 7.8 9 2.4
25.7 9 5.0 0.5
89.5 9 6.6 0.5
98.7 9 0.9 7.4 9 2.1
23.7 9 4.4 1.0
82.5 9 8.7 0.5
97.6 9 0.5 4.6 9 1.3
19.2 9 4.2 1.0
80.6 9 11 0.5
95.8 9 1.6 8.3 9 1.7
18.3 9 2.9 1.0
72.0 9 9.8 1.0
97.5 9 1.3 0.0
17.8 9 3.4 2.5
60.3 9 7.5 2.5
98.4 9 0.9
a
Values were expressed as mean 9 SE. There were 94–97 plants per treatment. Plants were grown under 16 h photoperiod and at 25 9 2°C.
nitrate on flowering were due to cerium or lanthanum.
3
.
4
. Effects on reproducti6e growth Thirty-five day-old plants growing in media
with 0.5 – 10.0 mM cerium nitrate were significantly taller than those growing in basal medium Fig.
1a. With 0.5 mM cerium nitrate, plant heights reached 13.0 cm compared to 7.9 cm in basal
medium. Combinations of cerium nitrate and lan- thanum nitrate did not show cumulative effects on
plant heights Fig. 1a.
The average dry weight of 35 day-old plants growing in media with 0.5 or 2.5 mM cerium
nitrate 350 and 379 mg respectively were signifi- cantly higher than those growing in basal medium
221 mg Fig. 1b. Dry weights of plants were also significantly higher with the addition of lanthanum
nitrate or both 0.5 – 2.5 mM Fig. 1b and Fig. 2.
Plants growing in basal medium produced an average of 7.4 flowers Fig. 3. The average num-
ber of flowers per plant in media containing cerium nitrate 0.5 – 10.0 mM ranged from 10.4 to
12.3. In media containing 0.5 – 10.0 mM lanthanum nitrate, the average number of flowers ranged
from 10.3 to 11.9 per plant Fig. 3. Plants grow- ing in media with cerium nitrate and lanthanum
nitrate 0.5 – 10.0 mM produced about 10.7 to 14.7 flowers. Medium containing combination of 2.5
m M cerium nitrate and 2.5 mM lanthanum nitrate
was observed most effective in flower production Fig. 2 and Fig. 3.
3
.
5
. Effects on the endogenous le6els of ZR, DHZR and IPA
Changes in endogenous levels of ZR, DHZR and IPA in leaf and root tissues of plants growing
in the basal medium and in the medium containing 0.5 mM cerium nitrate and 0.5 mM lanthanum
nitrate from day 12 to 18 were investigated. There was no significant difference in endogenous level
of ZR, DHZR and IPA between the tissues in the basal medium and in REE-supplemented medium
data not shown.
However, we noticed that the endogenous levels of ZR or DHZR in root tissues of plants in the
basal medium declined from about 218 or 249 pmolg.f.wt. on day 12 to 39.9 pmolg.f.wt. on day
18. The endogenous levels of IPA in root tissues
increased from 969 to 1351 pmolg.f.wt. on day 12 to 4057 – 4419 pmolg.f.wt. on day 16. Subse-
quently, a significant decrease in the level of IPA to
1120 – 1437 pmolg.f.wt
on day
18 was
observed.
3
.
6
. Effects on the endogenous le6els of carbohydrate in leaf tissues
There was no significant difference in endoge- nous levels of sucrose, glucose and fructose be-
tween the leaf tissues 12 – 18 days after seed germination in the basal medium and in REE-
supplemented medium data not shown. The lev- els of sucrose 0.7 – 1.1 mgg.f.wt remained stable
12 – 16 days after germination but decreased to about 0.1 mgg.f.wt. on day 18. In the control and
REE-treated leaf tissues, the levels of glucose and fructose on days 16 and 18 were significantly
higher than that on days 12 and 14 data not shown.
3
.
7
. Effects of
10
− 6
M IPA on root growth, plant height and flowering in the presence of
.
5
m M
cerium nitrate and .
5
m M lanthanum nitrate
IPA was found to be most effective on root growth and flowering among six naturally occur-
ring cytokinins tested data not shown. In order to further study the mechanism of action of REEs
on flowering, the effects of exogenous IPA with or without REEs on root growth and floral initiation
were investigated Table 3. Nine days after plants at 2-leaf stage 12 days after seed germination
were transferred to medium supplemented with 10
− 6
M IPA, root growth was observed signifi- cantly increased. On day 20 after seed germina-
tion, 32 of the plants in the medium containing 10
− 6
M IPA were observed to produce flower buds compared to none in the control medium.
However, addition of 10
− 6
M IPA significantly reduced plant height Table 3. Nine days after
plants at 2-leaf stage were transplanted to the medium with 10
− 6
M IPA, 0.5 mM cerium nitrate and 0.5 mM lanthanum nitrate, no beneficial ef-
fects on root growth were observed. Plant height and the percentage of plants with flower buds on
day 20 were further reduced Fig. 4, Table 3. The effects of 10
− 6
M IPA in the presence of 0.5 mM cerium nitrate and 0.5 mM lanthanum nitrate were
similar to that of 10
− 5
M IPA in terms of root growth and plant height.
Fig. 1. Effects of cerium nitrate and lanthanum nitrate on height a and dry weight b of A. thaliana 35 days after seed
germination. There were 100 plants per treatment. Bars indi- cate SE.
Fig. 2. Effects of 2.5 mM cerium nitrate and 2.5 mM lan- thanum nitrate on height and flower production of A. thaliana
35 days after seed germination. Plants were grown under 16 h photoperiod and at 25 9 2°C. Scale bar = 2.0 cm. A Control
plants. B Treated plants.
Fig. 3. Effects of cerium nitrate and lanthanum nitrate on the number of flowers produced 35 days after seed germination.
There were 100 plants per treatment. Bars indicate SE. Fig. 4. Effects of 10
− 6
M IPA on root growth and flowering in the presence of 0.5 mM cerium nitrate and 0.5 mM lan-
thanum nitrate. Plants were grown under 16 h photoperiod and at 25 9 2°C. Scale bar = 1.5cm. A 10
− 6
M IPA-treated plant. B 10
− 6
M IPA-treated plant in the presence of 0.5 m
M cerium nitrate and 0.5 mM lanthanum nitrate.
4. Discussion
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