Abstract:
Drought imparts injuries in plant through elevated production of reactive oxygen species viz.
(O
2
•
, OH
•
, H
2
O
2
and
1
O
2
). Potassium (K) triggers numerous ameliorative functions against
oxidative damages caused by drought. To investigate K attenuating oxidative damage and
promotion of antioxidant defense in wheat (Triticum aestivum L. cv. BARI Wheat-21), an
experiment was carried out at the Laboratory of Plant Stress Responses, Faculty of Agriculture,
Kagawa University, Japan, under controlled environment of green house during June, 2017 to
December, 2017. A total number of nine treatments were combined considering three K doses
viz. 0 mM (-K), 6 mM (+K) & 12 mM (+2K) in Hoagland nutrient solution exposed to 3 distinct
water regimes viz. 100% FC, 50% FC, and 20% FC for 9 days. The experiment was designed
in CRD model. Imposed drought stress notably reduced Plant height, fresh weight (FW), dry
weight (DW), leaf relative water content (RWC %) along with chlorophyll content in dose
dependent manner. Increased drought stress elevated the amount of oxidative markers viz.
malondialdelyde (MDA), hydrogen peroxide (H
2
iii
O
2
), methyl glyoxal (MG) and proline (Pro).
Wheat seedlings treated with drought stress resulted in notable decrease of ascorbate (AsA),
reduced glutathione (GSH) and increase of glutathione disulphide (GSSG). Enzymatic
activities of AsA-GSH cycle enzymes were declined except the ascorbate peroxidase (APX),
which was increased under drought stress combination. On the contrary, potassium (K) supply
resulted in improved Chlorophyll contents, and water status along with increased GSH content
and reduced the GSSG content which ultimately improved GSH/GSSG ratio. However, K
reduced MDA, H
2
O
2
, Proline contents and up regulated the antioxidant enzymes activities.
Exogenous K reduced the ROS production through increasing AsA. Additionally, In K treated
plant activities of glyoxalase I and glyoxalase II enzymes reduced the levels of MG and overall
increased the activity of glyoxalase system. However, plant showed better physiological
performances under 50% drought stress with 12 mM K was observed in the overall study.
Therefore it can be concluded that K confers drought stress tolerance in wheat seedlings through
up regulating antioxidant defense and glyoxalase system which helped in better seedling
establishment.
Description:
A Thesis
Submitted to the Faculty of Agriculture,
Sher-e-Bangla Agricultural University, Dhaka,
In partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
IN
AGRONOMY
