MPa Polyethylene Glycol Research Articles

Solute contributions to osmotic adjustment in leaf segments of wheat (Triticum aestivum L.) exposed to polyethylene glycol-induced water deficit

ABSTRACT This study examined osmotic adjustment (OA) and solutes accumulated in leaf segments of wheat cultivar Hartog exposed to polyethylene glycol (PEG)-induced water deficit (WD) in laboratory experiments. Additional 10 mM K+ or Na+ added to basal solution with PEG −0.5 MPa enhanced leaf OA by up to 100%. Omission of nitrogen from the basal solution suppressed the expression of OA in leaf segments, but the addition of 10 mM NO3 – increased leaf OA by up to 81%. K+ and glycinebetaine were not accumulated in leaf segments exposed to WD under PEG −0.5 MPa during 48 h, but Na+, Cl−, proline and total soluble sugars accounted for up to 21, 20, 7 and 40% of OA, respectively. Total soluble sugars were the largest contributor to OA and may also contribute to membrane stability. Further data are needed on accumulation of leaf NO3 − and glycinebetaine in response to increasing nitrogen supply, and on which other inorganic and organic solutes may also contribute to OA under PEG-induced WD. Laboratory experiments with leaf segments exposed to WD under −0.5 MPa PEG, and with 10 mM K+, Na+ or NO3 − added to the basal solution, could provide an effective and rapid pre-screen of diverse germplasm sources for OA expression. Selected genotypes should then be validated by exposure to soil WD for agronomic evaluation, and for OA expression under field WD.

Impact of seed priming on germination performance of fresh and aged seeds of Canola

Priming fresh and naturally aged canola seeds with different substances and observing the seed germination properties are involved in this work. Fresh seeds and aged seeds of canola cv. “süzer” were treated with distilled water, -0.8 MPa polyethylene glycol (PEG) 6000 and 50 mM thiamine for 8 hours. Storage of canola seeds showed the loss of germination capacity compared to fresh seeds. Present findings indicate that priming can improve germination and germination speed both in fresh and aged seeds of canola. Germination percentage increased in aged seeds with distilled water priming and thiamine priming. Mean germination times were lower in the primed seeds. Seedling growth didn’t improve with priming in both ages. It was concluded that germination performance improvement of aged seeds is possible with suitable priming.

Effects of osmopriming and storage temperature on the seed quality of Salvia przewalskii Maxim.

Salvia przewalskii Maxim. is an important Asian medicinal plant. The aim of the study was to investigate the reaction of seeds of this species to the priming and storage temperature. The germination, vigour and health of seeds were determined for untreated and osmoprimed diaspores, after harvest and 12 months of storage at 4 and 16°C. The seeds were primed in the polyethylene glycol (PEG) water solution with an osmotic potential of –0.8 and –1.1 MPa. It has been found that osmopriming of non-stored and stored seeds strongly reduced the time of germination. One-year storage of seeds both at 4 and 16°C caused statistically significant increase of the total number of germinating seeds, germination energy and capacity. The highest germination rate was found at the seeds stored at 16°C and primed with –0.8 MPa PEG solution.

Germination responses of two key mountain tree species to single and combined fire-related stresses: does elevational origin matter?

Since climate change is expected to increase fire activity and drought stress in forests across the globe, studying seed resistance to heat stress and drought is imperative to predict future mountain forest regeneration scenarios. Here, stress co-occurrence and among population variation in stress resistance are key elements to consider. We hypothesized that i) increasing heat/osmotic stress intensity decreases germination performance; ii) seeds from higher elevations (i.e. cooler and wetter climatic conditions) exhibit lower resistance to heat/osmotic stress showing a stronger decline in germination performance as compared to seeds from lower elevations (i.e. warmer and drier climatic conditions); and that iii) elevational differences in seed stress resistance vary depending on whether stresses are applied alone or in combination. We exposed seeds from Polylepis australis and Escallonia cordobensis from low (1200 – 1400 m), mid (1650 – 1800 m) and high (2000 – 2200 m) elevational origins to different heat (control, 75, 105 °C) and osmotic (0, -0.3, -0.6 MPa polyethylene glycol) stress intensities. Germination performance decreased with increasing heat/osmotic stress intensity and clear differences among elevational origins were observed. In both species low-mid elevation seeds showed lowest performances but exhibited slightly higher stress resistance than high elevation seeds; yet the nature of these responses was species-specific. Our results demonstrate that germination response to a combination of heat stress and drought is different from the response to each of these stresses applied individually. Therefore, understanding how interactions of climate change with fire events can influence germination timing and success in mountain trees requires considering the effect of multiple stressors on seed physiology. Our findings also highlight the potential population-specific and species-specific responses, which could be used as guidance for ongoing restoration plans.

Seed Viability and RNA Extraction Methods of Erythrina velutina Under Drought Stress

Abiotic stress caused by rigorous environmental conditions, such as drought, has negative effects on seeds. The species from arid and semiarid areas have mechanisms to maintain seed viability. In this study, the analyses of physical and physiological quality of the seeds of Erythrina velutina and their response to drought stress and RNA extraction methods were carried out. The seeds were collected from mother trees in two different provenances of natural occurrences of the species. The physical quality, viability, and vigor of the seeds were evaluated by morphometric parameters, germination, and electrical conductivity tests. The seeds were submitted to drought stress conditions for 0, 24, 48, and 72 hours on -0.8 MPa polyethylene glycol solution. To evaluate the viable RNA extraction method, the seed embryos were used for the extraction of this molecule and with an assessment of quantity and quality. The seeds from Pernambuco that were harvested in 2008 were bigger and presented lower vigor when in comparison to seeds that were harvested from Sergipe in 2012. The seeds under drought stress conditions presented null germination for all the treatments. After the drought stress, they were germinated on a paper substrate moistened with water, with better responses from the Lot Sergipe, 2012. The imbibition of seeds in the solution for 24 hours provides an increase in germination for less vigorous seeds, being indicated as a pre-germinative treatment. The RNA quality obtained by using a commercial extraction kit has better results, providing materials without contaminants when compared to the TRIzol method.

Nitric Oxide Signal, Nitrogen Metabolism, and Water Balance Affected by γ-Aminobutyric Acid (GABA) in Relation to Enhanced Tolerance to Water Stress in Creeping Bentgrass.

γ-Aminobutyric acid (GABA) plays an important role in regulating stress tolerance in plants. Purposes of this study was to determine the effect of an exogenous supply of GABA on tolerance to water stress in creeping bentgrass (Agrostis stolonifera), and further reveal the GABA-induced key mechanisms related to water balance, nitrogen (N) metabolism and nitric oxide (NO) production in response to water stress. Plants were pretreated with or without 0.5 mM GABA solution in the roots for 3 days, and then subjected to water stress induced by −0.52 MPa polyethylene glycol 6000 for 12 days. The results showed that water stress caused leaf water deficit, chlorophyll (Chl) loss, oxidative damage (increases in superoxide anion, hydrogen peroxide, malondialdehyde, and protein carbonyl content), N insufficiency, and metabolic disturbance. However, the exogenous addition of GABA significantly increased endogenous GABA content, osmotic adjustment and antioxidant enzyme activities (superoxide dismutase, catalase, dehydroascorbate reductase, glutathione reductase and monodehydroascorbate reductase), followed by effectively alleviating water stress damage, including declines in oxidative damage, photoinhibition, and water and Chl loss. GABA supply not only provided more available N, but also affected N metabolism through activating nitrite reductase and glutamine synthetase activities under water stress. The supply of GABA did not increase glutamate content and glutamate decarboxylase activity, but enhanced glutamate dehydrogenase activity, which might indicate that GABA promoted the conversion and utilization of glutamate for maintaining Chl synthesis and tricarboxylic acid cycle when creeping bentgrass underwent water stress. In addition, GABA-induced NO production, depending on nitrate reductase and NO-associated protein pathways, could be associated with the enhancement of antioxidant defense. Current findings reveal the critical role of GABA in regulating signal transduction and metabolic homeostasis in plants under water-limited condition.

Germination responses of Lycium humile, an extreme halophytic Solanaceae: understanding its distribution in saline mudflats of the southern Puna

Although knowledge about halophytic Solanaceae is scarce, it is known that several species within genus Lycium tolerate salinity. Lycium humile grows in highly saline soils in mudflats near saline Andean lakes. This study evaluated the germination responses of L. humile under different scarification methods, photoperiods, temperatures and saline conditions and, simultaneously, tested seedling survival under different iso-osmotic conditions. Dormancy and germination were found to be regulated by interactions with different factors, with the highest germination percentages being obtained by immersion in sulfuric acid, with a temperature of 25 °C and a temperature regime of 5/25 °C, under which seeds were neutrally photoblastic. As osmotic potential of saline solutions decreased, germination also decreased drastically but the seedling survival percentage was higher than 30 % at 600 mM NaCl. No seeds germinated in any of the polyethylene glycol (PEG) solutions and no seedling survival was observed from -1.2 MPa PEG solutions. More than 90 % of seeds incubated in NaCl were able to recover germination after being transferred to distilled water, independently of NaCl treatments. We concluded that the effects of extreme environmental conditions on germination responses and seed tolerance to salinity may determine the occurrence and restricted distribution of L. humile.

Factors controlling seed dormancy and germination response of Brachypodium hybridum growing in the hot arid mountains of the Arabian Desert

Seed dormancy and germination have been studied in the genetic model Brachypodium species complex in cooler, moist higher latitudes. Studying environmental factors in arid mountains affecting dormancy and germination in Brachypodium complex could determine the factors controlling these processes. This study assesses the impacts of temperature during seed maturation, seed after-ripening, drought, photoperiod, and thermoperiod on final germination and germination rate index of B. hybridum in the Arabian Desert. Seeds were germinated under dark or light conditions and under different ratios of red:far-red light, with three diurnal thermoperiods. The final germination percentage was significantly greater at 15/25 °C and 20/30 °C than at 25/35 °C and in light rather than in darkness. Seeds that reached maturity at 15/25 °C attained greater germination rates and faster germination than those that reached maturity at 20/30 °C. One-year after-ripening enhanced the final germination percentage and reduced photoperiod requirements. Light quality did not affect final germination percentage. The seeds tolerated drought of up to –0.8 MPa polyethylene glycol. The tolerance of B. hybridum seeds produced at higher thermoperiods to moderate levels of osmotic stress and their higher dormancy indicate that this species has the potential to survive the projected global warming in its native and introduced ranges.

Drought tolerance during germination depends on light and temperature of incubation in Salsola imbricata, a desert shrub of Arabian deserts

Plant recruitment in desert ecosystems is rare and highly unpredictable due to unfavourable conditions inhibiting germination events. Few studies addressed the impacts of water deficiency, temperature and light on germination of desert shrubs. Here, we assessed the impact of simulated drought (osmotic stress) as simulated by polyethylene glycol (PEG), light and temperature of incubation on seed germination of Salsola imbricata, a leaf succulent perennial shrub of the arid Arabian deserts. Fresh seeds were germinated in different osmotic potentials (0 up to -2.2 MPa PEG) at three temperatures and in two light regimes. In distilled water, germination was significantly greater at higher than at lower temperatures when seeds germinated in light, but the reverse was true in darkness. Both final germination and germination rate index (GRI) decreased gradually with the increase in osmotic stress, but the reduction was more pronounced at higher, compared to lower temperatures. Final germination and GRI decreased from around 70% and 49, respectively, in distilled water at both low and high temperatures to 44% and 39 in -1.4 MPa at low temperatures, but to 5% and 26, respectively, at higher temperatures. At higher temperatures, germination was significantly reduced in darkness, compared to light conditions, for most tested osmotic potentials. Most non-germinated seeds in PEG solutions recovered their germination when transferred to distilled water, indicating positive osmopriming effect for PEG. The temperature specific adaptation to lower osmotic potentials explains the ability of S. imbricata seeds to germinate early in seasons with little rainfalls.

Drought tolerance in alfalfa (Medicago sativa L.) varieties is associated with enhanced antioxidative protection and declined lipid peroxidation

Drought stress is considered the most adverse factor restricting plant survival, growth, and productivity. The identification of the key adaptive mechanisms to drought stress is essential to enhance the drought resistance of plants. In this study, differential responses of three alfalfa varieties to drought, including Medicago sativa L. cv. Longzhong (drought-tolerant), Longdong (moderate drought-tolerant), and Gannong No. 3 (drought-sensitive), were comparatively studied at morphological, physio-biochemical, and transcriptional levels after a 12-day period of drought stress simulated by −1.2 MPa polyethylene glycol (PEG-6000). The results showed that prolonged drought stress dramatically decreased growth and photosynthetic capacity of three alfalfa varieties while it increased the accumulation of malondialdehyde (MDA), reactive oxygen species (ROS), osmolytes and antioxidants including reduced ascorbate and glutathione, ascorbate peroxidase (APX) activities, and gene expression of antioxidative enzymes (MsCu/Zn-SOD, MsFeSOD, MtPOD, MsGPX, MsAPX, MsMDAR, MtDHAR, and MsGR). Nine days of treatment and some key traits, including the maximum quantum yield of photosystem II (Fv/Fm), the levels of MDA, O2−, and H2O2, the redox states of ascorbate and glutathione, APX activity, and the transcript levels of MsFeSOD, MsGR, and MsMDAR, might contribute to differentiating the drought stress tolerance in alfalfa. Overall, drought-tolerant Longzhong showed the highest water retention, photosynthetic performance, and osmoregulation capacity, the lowest lipid peroxidation, and the highest antioxidant enzyme activities and gene expression, which were mainly involved in the ascorbate-glutathione cycle to maintain the balance between the generation and scavenging of intracellular ROS. These findings highlight that enhanced antioxidative protection and declined lipid peroxidation play an important role in alfalfa tolerance against drought.

Influence of salinity and drought stresses on seed germination and seedling growth characteristics in sesame (Sesamum indicum L.)

In the present study, the potential for salt and drought tolerance of sesame genotypes were assessed. Seeds of three registered cultivars (Golmarmara, Muganli-57 and Uzun) were treated to seven levels (0, 25, 50, 75, 100, 150 and 200 mM) of NaCl to determine salinity influence on seeds. The drought condition was provided by Polyethylene glycol (PEG) induced water deficit. Seeds were germinated under stress of aqueous PEG solutions mixed to create water potentials of -2, -4, -6, -8 and -10 MPa. Effects of these abiotic stresses were assessed with the use of germination rate and early seedling growth traits which were root and shoot length, root fresh and dry weight, shoot fresh and dry weight. There is no germination at -8 and -10 MPa PEG applications for all the cultivars. Increasing concentrations of PEG from -2 to -6 MPa drastically reduced root length and the lowest value was recorded at -6 MPa. The cultivar, The treatment of different NaCl levels showed that increasing salt stress significantly decreased germination rate and seedling growth traits. The traits of the germination rate, root fresh weight and shoot dry weight were less affected at lower levels of salinity. However the concentration of >150 mM NaCI drastically reduced all the studied traits. The overall results suggest that germination and seedling growth traits were strongly inhibited by > -6 MPa PEG and 150 mM NaCl levels therefore lower concentrations should take into consideration for sustainable sesame production.

Drying and reduction in sensitivity to desiccation of seeds of Alibertia edulis: the influence of fruit ripening stage.

The intense environmental degradation in tropical regions suitable for agriculture has decreased native forest populations of plants with important fruits and medicinal properties. Alibertia edulis is a native tree from the Brazilian Cerrado. Knowledge about the effects of drying and storage on the physiological behavior of its seeds may aid in its sustainable exploitation and conservation. The goal of the present study was to determine which fruit ripening stage results in A. edulis seeds with higher tolerance to desiccation, and to investigate the effectiveness of polyethylene glycol (PEG) induced osmotic stress in combination with abscisic acid (ABA) in increasing seed desiccation tolerance during storage. Seeds were dried in activated silica gel (fast) or under ambient conditions (slow). Seeds originating from mid-ripe or fully ripe fruits exhibited better physiological performance than those obtained from green fruits. Slow drying resulted in seeds with high physiological potential. Seeds may be stored for up to 180 days without losing viability when treated with -0.73 MPa PEG without ABA.

Physiological and Proteomic Responses of Contrasting Alfalfa (Medicago sativa L.) Varieties to PEG-Induced Osmotic Stress.

Drought severely limits global plant distribution and agricultural production. Elucidating the physiological and molecular mechanisms governing alfalfa stress responses will contribute to the improvement of drought tolerance in leguminous crops. In this study, the physiological and proteomic responses of two alfalfa (Medicago sativa L.) varieties contrasting in drought tolerance, Longzhong (drought-tolerant) and Gannong No. 3 (drought-sensitive), were comparatively assayed when seedlings were exposed to -1.2 MPa polyethylene glycol (PEG-6000) treatments for 15 days. The results showed that the levels of proline, malondialdehyde (MDA), hydrogen peroxide (H2O2), hydroxyl free radical (OH•) and superoxide anion free radical (O2•-) in both varieties were significantly increased, while the root activity, the superoxide dismutase (SOD) and glutathione reductase (GR) activities, and the ratios of reduced/oxidized ascorbate (AsA/DHA) and reduced/oxidized glutathione (GSH/GSSG) were significantly decreased. The soluble protein and soluble sugar contents, the total antioxidant capability (T-AOC) and the activities of peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) first increased and then decreased with the increase in treatment days. Under osmotic stress, Longzhong exhibited lower levels of MDA, H2O2, OH• and O2•- but higher levels of SOD, CAT, APX, T-AOC and ratios of AsA/DHA and GSH/GSSG compared with Gannong No.3. Using isobaric tags for relative and absolute quantification (iTRAQ), 142 differentially accumulated proteins (DAPs) were identified from two alfalfa varieties, including 52 proteins (34 up-regulated and 18 down-regulated) in Longzhong, 71 proteins (28 up-regulated and 43 down-regulated) in Gannong No. 3, and 19 proteins (13 up-regulated and 6 down-regulated) shared by both varieties. Most of these DAPs were involved in stress and defense, protein metabolism, transmembrane transport, signal transduction, as well as cell wall and cytoskeleton metabolism. In conclusion, the stronger drought-tolerance of Longzhong was attributed to its higher osmotic adjustment capacity, greater ability to orchestrate its enzymatic and non-enzymatic antioxidant systems and thus avoid great oxidative damage in comparison to Gannong No. 3. Moreover, the involvement of other pathways, including carbohydrate metabolism, ROS detoxification, secondary metabolism, protein processing, ion and water transport, signal transduction, and cell wall adjustment, are important mechanisms for conferring drought tolerance in alfalfa.

EFFECT OF WATER STRESS AND CONTAMINATED WATER ON SEED GERMINATION TRAITS AND EARLY GROWTH IN MAIZE (Zea mays)

Irrigation is an increasingly important practice for sustainable agriculture. Water reuse as refined or non-refined wastewater can help agroecosystem productivity. Contaminated water may influence seed germination. Two experiments as laboratory and pot were carried out to assess impact of different levels of laundry detergent and water stress on seed germination and early growth in maize. At the laboratory experiment, seeds were treated with solutions of 0, -0.01, -0.09, -0.6 MPa polyethylene glycol 6000 and iso-osmotic concentration of laundry detergent. The pot experiment included different doses of laundry detergent (20, 2, 0.2 and 0 grams per litre) and two irrigation intervals (1 and 2-day irrigation interval). Results showed that -0.6 MPa osmotic potential reduced maize seed germination percentage, caulicle length, radicle length, seedling weight and seed vigor. 20 and 2 grams per litre of laundry detergent reduced plant height, leaf number per plant, leaf area, stem weight and leaf weight. 20 grams per litre of detergent increased specific leaf weight and reduced total biomass. The results show that irrigating maize by contaminated water with laundry detergent at high dose is not recommended.

Seed priming with cysteine modulates the growth and metabolic activity of wheat plants under salinity and osmotic stresses at early stages of growth

Wheat seeds were pretreated with 0.01 µM cysteine for 24 h and then exposed to salinity (300 mM NaCl) or osmotic (1.8 MPa polyethylene glycol) stress for 2 weeks. The results showed that salinity stress reduced the growth of seedlings and increased the oxidative damages. Salinity increased the proline and soluble sugar content. Salinity response could be attributed to more ion toxicity than dehydration effect, as dehydration due to PEG showed little response. According to the results of this investigation pretreatment of seed with cysteine can be used as a method to ameliorate salinity induced damages in plants. It can be concluded that the maximum effect of cysteine on salinity stress was to alleviate the oxidative damages through the increase in activity of antioxidant enzymes, glutathione content, and decrease the ion toxicity through increase in K+/Na+ ratio and inhibition of Na+ uptake. However this aspect requires further confirmation.

Comparison of the distribution of mineral nutrients and active substances in dehydration- and salinity-stressed Aloe vera L.

ABSTRACTChanges in growth and distribution of inorganic mineral elements and organic active substances in seedlings of A. vera were examined under treatments of −0.44 and −0.88 MPa polyethylene glycol 6000 (PEG) and corresponding isosmotic sodium chloride (NaCl). All stress treatments inhibited plant growth, with NaCl severely inhibiting the growth of the seedlings than PEG. However, leaf biomass did not change significantly. The nitrogen concentration under PEG was maintained higher than that under NaCl. Salinity caused more severe ionic imbalance than dehydration. However, when the concentration of NaCl was increased, ion homeostasis was maintained. Stressors induced an increase in aloin concentration in leaves, especially in young leaves. Polysaccharide concentrations in leaves did not change under dehydration. However, the polysaccharide concentration decreased in the middle and base leaves under NaCl. A. vera exhibited high adaptability to suitable osmotic stress, which increases its main active ingredients in leaves.

Physiological Studies on Six Wheat (Triticum Aestivum l.) Genotypes for Drought Stress Tolerance at Seedling Stage

Screening of drought tolerant varieties of wheat are important for ameliorating productivity of water scarce areas. Six wheat genotypes including two local checks were evaluated for drought tolerance against different osmotic stress levels induced by Polyethylene Glycol (PEG)6000. Experiment was set in completely randomized design (CRD) with three replicates and four treatments [0, -0.5 MPa, -0.75 MPa and -1.0 MPa PEG concentrations]. Wheat genotypes Khirman and Chakwal-86 were employed as check varieties. Four test genotypes evaluated were SD-621, SD-222, NIA Saarang and 22-03. Data were recorded on various seedling parameters such as germination percentage, germination index, shoot length, root length, fresh and dry weight of shoot and root, chlorophyll contents (a and b) and ionic contents (K+ and Ca2+, and K+ /Ca2+ ratio). No seedling survived at -1.0 MPa osmotic stresses. Best results were illustrated by wheat genotypes SD-222 and SD-621 with 98.89% and 96.7% germination at -0.5MPa and -0.75MPa osmotic stress, respectively. NIA Saarang and genotype 22-03 also exhibited better results at moisture stress. Reduction in chlorophyll and ionic contents was occurred with rise in water deficit in all genotypes. These findings appreciate the future use of these genotypes for obtaining high yield in water sparse areas.

Survival strategies of Ammopiptanthus mongolicus and Zygophyllum xanthoxylon in saline and drought environments, northwest China

Ammopiptanthus mongolicus and Zygophyllum xanthoxylon are typical plants in the West Ordos National Natural Reserve of Inner Mongolia, China. The populations of A. mongolicus had few young individuals and senesced. However, Z. xanthoxylon was growing well in the habitat of A. mongolicus. In addition, there is little information to compare their seed germination and seedling growth under combined salt and drought environments. In order to exploring the reason for the actuality, a study was conducted to quantify the interactive effects of salinity and drought stresses on seed germination and seedling growth of A. mongolicus and Z. xanthoxylon and then to compare the survival strategies of both shrubs. The experiment consisted of seven gradient concentrations of salinity (0, 0.3, 0.6, 0.9, 1.2, 1.5 and 1.8 % NaCl) in each of the six drought stress levels (0, −0.2, −0.4, −0.8, −1.6 and −2.0 MPa polyethylene glycol). As expected, combined salinity and drought stresses had significant (P < 0.05) interactive effects on seed germination of the two tested shrubs. There was significant decrease in these indices, in response to increased salt and/or drought stresses. The higher germination rate and shorter germination duration were detected for A. mongolicus, which may lead to the loss of seed bank. In addition, the radicle length of A. mongolicus (0–2.3 cm) was shorter than that of Z. xanthoxylon (0–14.6 cm), indicating less resistance of seedlings to the volatile conditions in the surface of arid soil. The stepwise regression analysis showed that salinity was the dominant influencing factor and followed by drought in seed germination and seedling growth under salt–drought mixed stress.

NO is involved in spermidine-induced drought tolerance in white clover via activation of antioxidant enzymes and genes.

Nitric oxide (NO), a key signaling molecule, can be induced by polyamines (PAs), which play an important role in improving drought tolerance in plants. This study was to further investigate the role of NO in spermidine (Spd)-induced drought tolerance associated with antioxidant defense in leaves of white clover (Trifolium repens) under drought stress induced by -0.3MPa polyethylene glycol (PEG-6000) solution. A hydroponic growth method was used for cultivating plants in a controlled growth chamber for 30-33days until the second leaves were fully expanded. Two relative independent experiments were carried out in our study. One is that exogenous application of Spd or an NO donor (sodium nitroprusside (SNP)) significantly improved drought tolerance in whole plants, as demonstrated by better phenotypic appearance, increased relative water content (RWC), and decreased electrolyte leakage (EL) and malondialdehyde (MDA) content in leaves as compared to untreated plants. For another detached leaf experiment, PEG induced an increase in the generation of NO in cells and significantly improved activities of nitrate reductase (NR) and nitric oxide synthase (NOS). These responses could be blocked by pre-treatment with a Spd biosynthetic inhibitor, dicyclohexyl amine (DCHA), and then reversed by application of exogenous Spd. Meanwhile, PEG induced up-regulation of activities and gene transcript levels of corresponding antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) to varying degrees, while these effects were partially blocked by pre-treatment with DCHA, the scavenger of NO, the inhibitors of NR or NOS. In addition, Spd-induced antioxidant enzyme activities and gene expression also could be effectively inhibited by an NO scavenger as well as inhibitors of NR and NOS. These findings suggest that both Spd and NO can enhance drought tolerance. Spd was involved in drought stress-activated NR and NOS pathways associated with NO release, which mediated antioxidant defense and thus contributed to drought tolerance in white clover.

Deciphering priming-induced improvement of rapeseed (Brassica napus L.) germination through an integrated transcriptomic and proteomic approach

Rape seeds primed with −1.2MPa polyethylene glycol 6000 showed improved germination performance. To better understand the beneficial effect of osmopriming on seed germination, a global expression profiling method was used to compare, for the first time, transcriptomic and proteomic data for osmoprimed seeds at the crucial phases of priming procedure (soaking, drying), whole priming process and subsequent germination. Brassica napus was used here as a model to dissect the process of osmopriming into its essential components.A total number of 952 genes and 75 proteins were affected during the main phases of priming and post-priming germination. Transcription was not coordinately associated with translation resulting in a limited correspondence between mRNAs level and protein abundance. Soaking, drying and final germination of primed seeds triggered distinct specific pathways since only a minority of genes and proteins were involved in all phases of osmopriming while a vast majority was involved in only one single phase. A particular attention was paid to genes and proteins involved in the transcription, translation, reserve mobilization, water uptake, cell cycle and oxidative stress processes.