>Magister Scientiae - MSc / There is an influx in heavy metals into soils and ground water due to activities
such as increased mineral mining, improper watering and the use of heavy metal
contaminated fertilizers. These heavy metals are able to increase the ROS species
within plants which may result in plant metabolism deterioration and tissue
damage. Heavy metals may also directly damage plants by rendering important
enzymes non-functional through binding in metal binding sites of enzymes. The
heavy metal focused on in this study was vanadium due to South Africa being
one of the primary produces of this metal. Two related Brassica napus L cultivars
namely Agamax and Garnet which are economically and environmentally
important to South Africa were exposed to vanadium. Physiological experiments
such as cell death, chlorophyll and biomass determination were conducted to
understand how these cultivars were affected by vanadium toxicity. A low cost,
sensitive and robust vanadium assay was developed to estimate the amount of
vanadium in samples such as water, soils and plant material. The oxidative state
as well as the antioxidant profile of the two cultivars were also observed under
vanadium stress. A chlorophyll assay which was conducted on the two cultivars exposed to vanadium showed a marked decrease in chlorophyll A in the
suspected sensitive cultivar which was Garnet. However, the suspected tolerant
cultivar Agamax fared better and the decrease in chlorophyll A was much less. A
similar trend was observed for the two cultivars when the cell death assay was
conducted. The vanadium assay showed that Garnet had higher concentrations
of vanadium within its leaves and lower concentrations in its roots when
compared to Agamax. This observation displayed that Agamax had inherent
mechanisms which it used to localize vanadium in its roots and which assisted in
its tolerance to the vanadium stress.
The oxidative state was determined by doing assays for the specific reactive
oxygen species namely hydrogen peroxide and superoxide. It was observed that
vanadium treated Garnet leaves had higher reactive oxygen species (ROS)
production when compared to the Agamax treated leaves. In-gel native PAGE
activity gels were conducted to determine the antioxidant profile for the two
cultivars which were exposed to vanadium. The antioxidant enzymes which were
under investigation were ascorbate peroxide (APX), superoxide dismutase (SOD)
and glutathione-dependent peroxidases (GPX-like) as these enzymes are known
to be responsible for controlling the ROS produced in the plants. The GPX-like
profile consisted of three isoforms. No isoforms were inhibited by vanadium
treatments but one isoform had increased activity in both the Garnet and
Agamax treated samples. The SOD profile for Garnet consisted of six isoforms and Agamax had seven isoforms. One isoform which was visualized in both
Agamax as well as Garnet was inhibited by vanadium treatments. Agamax also
had two isoforms which were up-regulated however the corresponding isoforms
in Garnet showed no change. The Ascorbate peroxidase profile consisted of
seven isoforms for both Garnet and Agamax. No isoforms were inhibited by
vanadium treatment. Three isoforms were up-regulated in Garnet and Agamax
under vanadium treatments.
Here, it is illustrated that Garnet lacked certain mechanisms found in Agamax
(and thus experienced more cell death, yield and chlorophyll loss) and performed
worst under high vanadium concentrations. Although Garnet increased the
activity of some of its antioxidant isoforms in response to increasing ROS levels it
was not adequate to maintain a normal oxidative homeostasis. This disruption in
oxidative homeostasis lead to plant damage. Agamax was observed to produce
less ROS than Garnet and was able to control the ROS produced more effectively
than Garnet and thus less damage was observed in Agamax.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uwc/oai:etd.uwc.ac.za:11394/4252 |
| Date | January 2013 |
| Creators | Gokul, Arun |
| Contributors | Keyster, Marshall |
| Publisher | University of the Western Cape |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Rights | University of the Western Cape |
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