Abstract:
Salinity and drought stress is the major and frequently co-occurring abiotic stresses
which disturb the morphophysiological and biochemical attributes within the plants.
Therefore, the present study was conducted to investigate the morphophysiological
and biochemical responses of two popular cultivars of rice (BRRI dhan29 and BRRI
dhan48 from indica and Koshihikari from japonica) under salinity and drought stress
either alone or in combination at early vegetative stage. Eighteen-day-old seedlings
were subjected to salinity (150 mM NaCl), drought (PEG-6000, 15%) and combined
salinity and drought (150mM NaCl + PEG-6000, 15%) in vitro for 72h. Salinity and
drought alone and in combination increased mortality rate, decreased seedlings
height, reduced biomass, abated water status and lowered photosynthetic pigments
content in all three cultivars but the worst effects were observed in BRRI dhan29 and
Koshihikari compared to BRRI dhan48. Moreover, under stress conditions compared
with control a substantial increase was seen in the rate of electrolyte leakage (EL),
elevated levels of H
2
O
, lipoxygenase (LOX) activity, malondialdehyde (MDA) and
methylglyoxal (MG) content which indicated an enhancement of lipid peroxidation
in rice cultivars. The reduction of reduced ascorbate (AsA), lower AsA/DHA and
GSH/GSSG ratio under salinity stress and combined stress indicate the disruption of
redox balance in the cell. But under stress conditions compared with other varieties
BRRI dhan48 showed lower Na
2
+
/K
+
ratio, elevated proline (Pro.) content, higher
AsA and reduced glutathione (GSH) activity, higher AsA/DHA and GSH/GSSG
ratio and enhanced activities of MDHAR, DHAR, GPX and glyoxalase system. The
results suggested that higher tolerant capacity of BRRI dhan48 against salinity,
drought and combined stress is related to lower Na
iii
+
/K
+
ratio, enhanced Pro content
and better performance of glyoxalase system and antioxidant defense for scavenging
reactive oxygen species (ROS) and these results may provide insight into possible
responses associated with single or combined stress of salinity and drought in rice
cultivars.
Description:
A Thesis
Submitted to the Faculty of Agriculture
Sher-e-Bangla Agricultural University, Dhaka,
in partial fulfilment of the requirements
for the degree of
MASTER OF SCIENCE
IN
AGRONOMY
