Responses of Lowland, Upland and Aerobic Rice Genotypes to Water Limitation During Different Phases

Rice yield reduction due to water limitation depends on its severity and duration and on the phenological stage of its occurrence.We exposed three contrasting rice genotypes,IR64,UPLRi7 and Apo(adapted to lowland,upland and aerobic conditions,respectively),to three water regimes(puddle,100%and 60%field capacity)in pots during the vegetative(GSI),flowering(GSII)and grain filling(GSIII)stages.Stress at all the three stages significantly reduced yield especially in lowland genotype IR64.Effect of water limitation was more severe at GSII than at the other two stages.Stress at GSI stage reduced both source activity(leaf area and photosynthetic rate)and sink capacity(tiller number or panicle number per pot).When stress was imposed at GSII,spikelet fertility was most affected in all the three genotypes.In both GSII and GSIII,although leaf area was constant in all the three water regimes,estimated relative whole-plant photosynthesis was strongly associated with yield reduction.Reduced photosynthesis due to stress at any given stage was found to have direct impact on yield.Compared to the other genotypes,Apo had deeper roots and maintained a better water relation,thus,higher carbon gain and spikelet viability,and ultimately,higher biomass and productivity under water-limited conditions.Therefore,screening for these stage-dependent adaptive mechanisms is crucial in breeding for sustained rice production under water limitation.

A Simple and Rapid Oxidative Stress Screening Method of Small Molecules for Functional Studies of Transcription Factor

Structure-assisted reverse chemical discovery approaches are becoming attractive due to target based screening.However,Small molecules(SMs)identified by reverse chemical genetic approach require robust phenotyping assays to study the plant responses.We optimized a screening method in rice seedlings using methyl viologen(MV)induced oxidative stress under high light conditions.This method was suitable for studying the efficacy of SM targeting oxidative stress related genes.Structure-assisted drug designing approach was used to identify SM targeting DREB2A transcription factor(TF).Rice seedlings treated with pronetalol showed susceptible phenotype when exposed to oxidative stress.Pronetalol inhibited the DREB2A activity and suppressed the expression of its target LEA7 and HSFA3 genes under oxidative stress.The assay is quite simple and robust and can be expanded to high throughput screening method for functional validation of TF.

Acquired Traits Contribute More to Drought Tolerance in Wheat Than in Rice

Drought tolerance is governed by constitutive and acquired traits.Combining them has relevance for sustaining crop productivity under drought.Mild levels of stress induce specific mechanisms that protect metabolism when stress becomes severe.Here,we report a comparative assessment of“acquired drought tolerance(ADT)”traits in two rice cultivars,IR64(drought susceptible)and Apo(tolerant),and a drought-tolerant wheat cultivar,Weebill.Young seedlings were exposed to progressive concentrations of methyl viologen(MV),a stress inducer,before transferring to a severe concentration.“Induced”seedlings showed higher tolerance and recovery growth than seedlings exposed directly to severe stress.A novel phenomic platform with an automated irrigation system was used for precisely imposing soil moisture stress to capture ADT traits during the vegetative stage.Gradual progression of drought was achieved through a software-controlled automated irrigation facility.This facility allowed the maintenance of the same level of soil moisture irrespective of differences in transpiration,and hence,this platform provided the most appropriate method to assess ADT traits.Total biomass decreased more in IR64 than in Apo.The wheat cultivar showed lower levels of damage and higher recovery growth even compared to Apo.Expression of ROS-scavenging enzymes and drought-responsive genes was significantly higher in Apo than in IR64,but differences were only marginal between Apo and Weebill.The wheat cultivar showed significantly higher stomatal conductance,carbon gain,and biomass than the rice cultivars,under drought.These differences in ADT traits between cultivars as well as between species can be utilised for improving drought tolerance in crop plants.