Medicinal Plant Research 2015, Vol.5, No. 6, 1-9
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Figure 4 Scanning electron micrographs of O. basilicum showing effects of different concentrations of arsenic on morphology of
peltate glandular trichomes.
(A) Control: Mature peltate trichome. Arrow indicates cuticle in central part showing a buldge, possibly corresponding to
sub-cuticular cavity underneath.
(B) 10 mg/kg As: Mature peltate trichome on adaxial leaf surface.
(C) 50 mg/kg As: Mature peltate trichome with torn cuticle sheath, disclosing the head cells.
(D) 150 mg/kg As: Sunken trichome.
Transmission electron micrographs of glandular cells of peltate trichome in the active secretory stage under different concentrations
of arsenic. (cw: cell wall, rer: rough endoplasmic reticulum, m: mitochondria, n: nucleus, v: vacuole, d: dictyosome, pd:
plasodesmata). (Bar = 1µm)
(E-F) Control and 10 mg/kg As: Details of cytoplasm and organelles in secretory cells.
(G) 50 mg/kg As: Large-shaped mitochondria. Plasmodesmata in the secretory cell walls (arrow).
(H) 150 mg/kg As: Secretory cell showing peripheral nucleus and mitochondrial aberrations in the form of inflated cristae.
for a continuous supply of carbon precursors. EO
production is also dependent on availability of various
nutrient ions in soil. Any disruption in the nutrient
balance reduces the oil production as observed in basil
plants exposed to higher level of As in soil. Such
results have also been observed in plants growing in
saline soils. Reduction in EO yield due to high dose
of 100 mM NaCl has been observed in
Salvia
officinalis
(Ben Taarit et al., 2009)
and
Origanum
majorana
(Baatour et al., 2010). As in soil disturbs the
ionic balance and availability of nutrient ions to plant
systems as observed in response to salinity.
Comparison of plant biomass and oil content at
different treatments revealed that As stress showed
more severe effect on biomass than on oil content.
This low reduction of oil content is certainly an
advantage for EO plants. Biswas et al. (2011) in a
detailed review have attributed the changes in oil yield
in various EO plants to cascading effects of stress
imposed on account on salt, heavy metal or water
availability. Stress encountered by the plants affects
the presence and availability of nutrient elements, and
hence the secretory pathway.
Ultrastructual studies of secretory structures of trichomes
showed early maturity in plants grown in As amended
soil. At 150 mg/kg As, structure of head c ell
changed from globular to mushroom-like and the
trichomes were seen embedded into the epidermal
surface. Such changes are generally observed in
trichomes at post secretory stage (Gravano et al.,
1998). Werker et al. (1993) also observed that in
O.
basilicum
glandular trichomes were embedded in the
epidermis when trichomes attain maturity and proceed
to senescence. Premature senescence of trichomes is
distinctly observed in the present studies in response
to As toxicity.
At 10 mg/kg As trichome ultrastructure did not show
any variation in comparison to trichomes of control
plants. At both the treatments, the head cells showed
highly-organized cytoplasm, large nuclei, and many
