Study On Seed Osmopriming For Alleviation Of Stresses During Post-Germinative Seedling Growth In Wheat

Wheat(Triticum aestivum L.)is the second most important food crop in the world and the most widely grown cereal in temperate environments.Environmental constraints like water and temperature stress frequently effect wheat crop during its critical phases of establishment.Low heritability of the traits and limiting conditions in the process of testing and selection for the development of tolerant genotypes has led to the recognition of priming techniques.Pre-sown seed treatments techniques such as seed osmopriming has been proved to be successful in inducing stress resistance during seed germination.Seed osmopriming is a process of controlled seed imbibition in solution of higher osmotic potential aiming to initiate germination related process under stressful condition without reaching the level of embryo cell elongation and radicle protrusion before which seeds are re-dried back to original moisture level.Though seed priming has been known for over two decades,there has been a dearth of information about possible stress alleviation effects of seed osmopriming during post germinative seedling establishment and growth.The objective of this study was to evaluate the potential of seed osmopriming in alleviation of stress conditions frequently occurring during seedling establishment and early plant growth.Further we intended to elucidate diffusion effects of stress imprints induced by seed osmopriming during normal seed germination and establishment under normal conditions.Initially an experiment was conducted to optimize seed osmopriming protocol for enhanced stress resistance in winter wheat cultivar Yangmai16.For that purpose wheat seeds were osmoprimed under three different polyethylene glycol solutions of 0,-0.3,-0.6 and-0.9 MPa;all under 14,18 and 23? temperatures.We aimed to select seed osmopriming protocol that results in maximum imbibition duration thus longest Phase II of germination process without adversely affecting the seeds.Further re-dried osmoprimed seeds through each combination of osmotic potential and temperature were germination under normal as well as osmo-stress and low temperature stress.Both osmotic potential of the solution and temperature during seed osmopriming had significant effect on seed moisture absorption,percent radicle protrusion as well as on mean seed germination time,starch degradation and antioxidant activity during subsequent germination under normal and stress conditions.From the data acquired osmotic potential of-0.9 MPa together with 180C temperature for 30 h was selected as optimal seed osmopriming protocol for seeds of winter wheat.The potential of selected seed osmopriming protocol for induction of osmo-stress resistance was elucidated in seedlings germinated under normal conditions for 48 h and osmo-stressed for proceeding 7 d.Seed osmopriming mediated improved seedling growth was evident from significantly higher plant biomass and plant height under control conditions when compared to non-osmoprimed controls.As a result of seed osmopriming,under osmo-stress conditions root biomass,root length as well as root surface area increased significantly when compared to seedling from non-osmoprimed seeds.Plants from osmoprimed seeds translocated and accumulated higher level of soluble sugars in roots mainly for osmotic adjustment.In response to osmo-stress,content of proline in the roots of the seedlings from osmoprimed seeds was recorded 30.01%higher than in the roots of the seedlings from non-osmoprimed seeds.Further,higher antioxidant activity and lower membrane damage were responses to osmo-stress as a result of seed osmopriming.From the data we concluded that seed osmopriming induced stress resistance was accompanied with advanced germination,higher osmolytes accumulation and enhanced antioxidant activity.The detailed evaluation of seed osmopriming mediated root growth and antioxidant activity for alleviation of osmo-stress in 12 d old wheat seedlings revealed that higher root elongation equipped the seedlings from osmoprimed seed with the ability to excess remote moisture.After 40 h of osmo-stress increase in root length accounted 87.29%as a result of seed osmopriming and that was twice the increase of that in non-osmoprimed seedlings.Substantial increase in production of root hairs in response to water stress was evident from 29.11%higher root surface area in seedlings from osmoprimed seeds compared to the seedlings from non-osmoprimed seeds.Further,seed osmopriming resulted into reduced accomulation of reactive oxygen species(ROS)under osmo-stress which was evident from 8 to 10%lower content of superoxide radical(O2·-)after 6 h of osmo-stress compared to seedlings from non-osmoprimed seeds.Seed osmopriming resulted into significantly higher activity of superoxide dismultase(SOD)and peroxidase enzymes to reduce ROS accumulation thus reduced malondialdehyde(MDA)concentration by 50%when compared to seedlings from non osmoprimed seeds.Stress imprints induced by seed osmopriming resulted into production of efficient root system to acquire and utilize moisture as well as enhanced antioxidant system more capable of avoiding and/or scavenge the production of ROS generated during osmo-stress.Wheat seedlings at 3 leaf stage grown from both osmoprimed and non-osmoprimed seeds as well as early stress acclimated seedlings grown from non-osmoprimed seeds were osmo-stressed to evaluate the potential of wheat seed osmopriming for induction of osmo-stress resistance and its diffusion effects.Seed osmopriming and early stress acclimation,resulted into significantly higher root biomass and longer total root length under osmo-stress when compared to non-osmoprimed-non-acclimated plants.Plants from osmoprimed seeds maintained higher level of soluble sugar under control conditions and in response to osmo-stress both seed osmopriming and plant stress acclimation resulted into significantly higher content of proline.Improved antioxidant capacity as a result of seed osmopriming and early stress acclimation was evident from relatively higher activity of SOD in the roots recorded 18 h after commencement of osmo-stress.Osmo-stress pretreatment of plant for stress acclimation reduced plant biomass and significantly affected photosynthetic activity along with induction of osmo-stress tolerance.While seed osmopriming induced osmo-stress resistance was accompanied with improved seedling establishment and higher osmolytes accumulation.Stress imprints induced by seed osmopriming were found to be recruited to alleviate chilling stress in 12 d old wheat seedlings.8 h after chilling stress induction,seed osmopriming resulted into significantly reduced accumulation of O2·-and hydrogen peroxide compared to the seedlings arise from non-osmoprimed seeds.Immediately,after the chilling stress the activity of SOD in osmoprimed plants increased which in turn decrease MDA concentration.Plants grown from osmoprimed seeds appeared to be more capable of scavenge the production of ROS generated during chilling stress.Alleviation of chilling stress by seed osmopriming shows stress cross talk ability of seed osmopriming induced stress imprints.Thus seed osmopriming can be considered a reliable and feasible tool to cope with chilling conditions that occur frequently during early seedling establishment of winter wheat.Seed osmopriming mediated stress alleviation effect was found to be a result of response mechanism induced during seed osmopriming treatment.The re-drying of the seeds after osmopriming,short time storage as well as germination and plant establishment under normal condition did not affect the induced memory.Thus,wheat seed osmopriming can be used to induce stress imprints to cope with the event of osmo and chilling stress that occur during early crop growth stages.