Medicinal Plant Research 2015, Vol.5, No. 6, 1-9
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Table 1 Effect of arsenic on shoot length, fresh wt. and dry wt. of Ocimum basilicum.
Values with different letters (a-d) are significantly different at
p
≤ 0.05 (means of three replicates ± S.D.).
Table 2 Effect of arsenic on essential oil composition of
Ocimum basilicum
.
Compounds
0 mg/kg
10 mg/kg As
50 mg/kg As
150 mg/kg As
Methyl cinnamate
0.013±0.005
0.0036±0.00
nd
nd
Linalool
0.0013±0.00 a
0.005±0.00 c
0.0047±0.00 bc
0.004±0.00 b
Methyl eugenol
0.028±0.00 e
0.006±00 bd
0.008±0.00 cd
0.001±0.00 a
1,8-cineol
0.009±0.001 c
0.005±0.00 b
0.0036±0.00 a
0.0029±0.00 a
Camphor
0.0072±0.00
nd
nd
nd
nd: not detected Values with letters (a-e) are significantly difference at
p
≤ 0.05 (means of three replicates ± S.D.).
more prominent on the secretory cell wall and large
mitochondria were seen (Figure 4. 4G). At 150 mg/kg
As, glandular trichomes showed various changes
at structural and ultrastructural level. The sectretory
cells showed less number of vacuoles. RER were well
represented but size of mitochondria was observed to
be reduced (Figure. 4H).
2.
Discussion
Results of the present study clearly demonstrate that
the growth of
O. basilicum
significantly decreased as
a result of higher As phytotoxicity, though at lower As
concentrations the effect was not significant. An
increase in plant growth at 10 mg/kg As in soil was
observed. Results are in agreement with the study on
Scutellaria biacalensis
, an important herbal plant used
in traditional Chinese medicine where low levels of
As in soil stimulated the growth and development
(Cao et al., 2009). This positive response at lower As
concentrations can be linked to phosphorous uptake.
Phosphate and arsenate are taken into plant roots by a
common carrier. However, the phosphate/plasma
membrane carrier has much higher affinity for
phosphate than arsenate (Meharg and Macnair, 1990).
Phosphate is also reported to be an efficient
competitive inhibitor of arsenate uptake (Meharg and
Macnair, 1990). At low soil As concentration, displacement
of soil phosphate by arsenate increases the availability
of phosphate to the plants, which results in the
increase of growth.
Four-fold increase in EO yield in plant tissues was
observed when As concentration in the soil was raised
up to 50 mg/kg, whereas at 150 mg/kg As the oil yield
significantly decreased by about 60% in comparison
to control. Heavy metal-induced enhancement in EO
yield at low concentration in growth medium has been
reported earlier in other EO yielding species such as
Matrica chamomilla
(Nasiri et al., 2010),
Mentha
piperita
(Prasad et al., 2010) and
Salvia officinalis
(Stancheva et al., 2009). Increase in the EO content by
the application of heavy metals is not properly
understood, but the change has been attributed to the
effect of metallic elements on the enzyme activity and
carbon metabolism which further affects the EO
synthesis pathways (Prakash and Kardage, 1980).
Increase in EO production and density of EO releasing
trichomes in
O. basilicum
has been observed in the
present study at moderate As levels. This can be
a partial explanation for the observed higher oil
content per unit leaf dry weight. According to Charles
et al. (1990) EO accumulation increases indirectly by
interfering with net assimilation rate of nutrients in
plants or by unequal partitioning and distribution of
resources for growth and differentiation. EO
production in basil leaves was strongly inhibited
at 150 mg/kg As. Reduction in photosynthesis and/or
additional changes in metabolic system are probably
responsible for this inhibition. According to Croteau
and Johnson (1984) EO biosynthesis takes place in
epidermal oil glands that are carbon heterotrophic and
thus depend on the adjoining photosynthesizing cells
Arsenic (mg/kg soil)
Shoot length
Shoot FW
Shoot DW
0
47.33±1.16 c
36.50±2.50 c
3.10±0.17 b
10
68.96±0.87 d
60.33±2.08 d
5.16±0.37 c
50
40.90±1.65 b
32.73±1.55 b
3.23±0.61 b
150
30.93±1.44 a
24.90±0.65 a
2.26±00 a
