MOLECULAR ANALYSIS OF JASMONIC ACID & POLYAMINES SYNTHESIS & SIGNALING UNDER HEAT & DROUGHT STRESS IN RICE
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Date
2017
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DIVISION OF PLANT PHYSIOLOGY ICAR-INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
Rice (OryzasativaL.) is the most important food crop and grown mainly in tropical
and subtropical zones.Under current climate change scenarioheat and drought stress
have been reported to affect rice productivity. To address the challenges posed by
climate change, identifying true sources of heat and drought tolerance and finding
reliable ways to ameliorate the effect of these stresses is the need of hour. The present
investigation was conducted to test the potential role of polyamines (PAs) and
jasmonic acid (JA) in ameliorating the impact of drought and heat stress at anthesis
stage in rice. The study was planned with ten genotypes namely N-22, N-L-44,
SahbhagiDhan, CR-262-4, Anjali, Vandana, IR-64, PB-1, Swarna and PS-5, raised
under normal environment and exposed to drought and heat stresses at anthesisduring
2013-14. Before exposure to stress (at booting stage), the plants were pre-treated with
phytohormones JA (1mM) and PAs (a mixture of Put, Spd and Spm with 0.5 mM
concentration of each). All the ten genotypes showed reduction in pollen viability (PV),
spikelet fertility (SF) and panicle grain weight (PGW) under both the stresses. Four
genotypes Swarna, IR-64, PB-1 and PS-5 showed more reductions in above traits and
were considered most sensitive to both the stresses. SahbhagiDhan, Vandana, Anjali and
CR-262-4 were found moderately tolerant to stress compared to others. N-22 and NL-44
showed least reductions under stress in panicle grain weight and considered as
tolerant types. Exogenous application of the PAs and JA showed marginal
improvement in PV, SF and PGW.During 2014-2015, four genotypes from above viz.
N-22, N-L-44, Swarna and PS-5 were selected based on their performance under
above stresses and used for physiological, biochemical and molecular traits like
RWC, MSI, H2O2, TBARS, SOD, endogenous level of hormones (PAs and JA) and
relative expression of genes involved in synthesis and signalling of these hormones.
In general, RWC and MSI decreased and H2O2, TBARS and SOD increased under
stress in all genotypes. Reduction in RWC and MSI and increase in H2O2, TBARS
were more in sensitive genotypes (Swarna and PS-5) compared to tolerant types (N22
and N-L-44). SOD activity increased more in tolerant genotypes. PV, SF and
panicle grain weight gave almost similar results like previous year i.e. all the three
traits decreased significantly under both the stresses. Exogenous application of JA and
PAs did not show any ameliorative effect on any of the parameters under both the
stresses. Under drought condition Put contentof tolerant genotypes N-22 and N-L-44
increased significantly (179.3% and 193.5% respectively), whereas, in Swarna and
PS-5 increased by 171.9% and 94.1% respectively. Under heat stress condition
increase in Put level was not significant. Under drought condition JA contentof
tolerant genotypes N-22 and N-L-44 increased by 57.3% and 85.7%, respectively,
whereas, the sensitive genotypes Swarna and PS-5 shown an increase of 42% and
32.7%, respectively. Under heat stress conditionsthere was no significant change in
JA levels. Similar trend was observed for relative expression of genes involved in
synthesis and signalling of PAs (samdc, adc-1, adc-2 and myb-8) and JA (aos, aoc,
opr, coi-1, rsOspr-10 and jaz). This indicates that both PAs and JA may have
important role in drought stress alleviation. However, exogenous application of JA
and PAs did not show any appreciable changes. One of the reason for insignificant
effect of exogenous application of phytohormones could be the lower concentrations
applied. Functional validation of Osjazgene was done in Arabidopsis plant. OE-JAZ
transgenic plant showed more expression of Osjazgene compared to WT (Wild Type)
plants under stress. Osjazis a repressor of JA signalling and we found that OE-JAZ
transgenic linesshowed less increase in endogenous level of JA compared to WT
under drought conditions. Findings of this study conclude that pre-treatment with 0.5
mM concentration of PAs and 1.0 mM concentration of JA was not effective to
ameliorate the effects of drought and heat stress effect on PV, SF and PGW. But both
the growth regulators lowered the level of oxidative stress induced by drought and
heat stress, but the magnitude of impact was not effective to show changes in PV, SF
and PGW. It indicates that the changes in the endogenous level of PAs and JA due to
application of both the growth regulators were less than the threshold levels required
to ameliorate the effect of heat and drought stress. The study may be further
undertaken in future with different and higher concentrations of phyto-hormones
which could enhance the endogenous levels up to reach the threshold levels for their
amelioration effects under heat and drought stress in rice
Description
t-9560
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