Reduced Water Potential Research Articles

Insight of PBZ mediated drought amelioration in crop plants.

Water scarcity is a significant environmental limitation to plant productivity as drought-induced crop output losses are likely to outnumber losses from all other factors. In this context, triazole compounds have recently been discovered to act as plant growth regulators and multi-stress protectants such as heat, chilling, drought, waterlogging, heavy metals, etc. Paclobutrazol (PBZ) [(2RS, 3RS)-1-(4-chlorophenyl)- 4, 4-dimethyl-2-(1H-1, 2, 4-trizol-1-yl)-pentan-3-ol)] disrupts the isoprenoid pathway by blocking ent-kaurene synthesis, affecting gibberellic acid (GA) and abscisic acid (ABA) hormone levels. PBZ affects the level of ethylene and cytokinin by interfering with their biosynthesis pathways. Through a variety of physiological responses, PBZ improves plant survival under drought. Some of the documented responses include a decrease in transpiration rate (due to reduced leaf area), higher diffusive resistance, relieving reduction in water potential, greater relative water content, less water use, and increased antioxidant activity. We examined and discussed current findings as well as the prospective application of PBZ in regulating crop growth and ameliorating abiotic stresses in this review. Furthermore, the influence of PBZ on numerous biochemical, physiological, and molecular processes is thoroughly investigated, resulting in increased crop yield.

Combating Salinity Through Natural Plant Extracts Based Biostimulants: A Review.

Enhanced crop growth and yield are the recurring concerns in agricultural field, considering the soaring world population and climate change. Abiotic stresses are one of the major limiting factors for constraining crop production, for several economically important horticultural crops, and contribute to almost 70% of yield gap. Salt stress is one of these unsought abiotic stresses that has become a consistent problem in agriculture over the past few years. Salinity further induces ionic, osmotic, and oxidative stress that result in various metabolic perturbations (including the generation of reactive oxygen, carbonyl, and nitrogen species), reduction in water potential (ψw), distorted membrane potential, membrane injury, altered rates of photosynthesis, leaf senescence, and reduced nitrogen assimilation, among others); thereby provoking a drastic reduction in crop growth and yield. One of the strategies to mitigate salt stress is the use of natural plant extracts (PEs) instead of chemical fertilizers, thus limiting water, soil, and environmental pollution. PEs mainly consist of seeds, roots, shoots, fruits, flowers, and leaves concentrates employed either individually or in mixtures. Since PEs are usually rich in bioactive compounds (e.g., carotenoids, flavonoids, phenolics, etc.), therefore they are effective in regulating redox metabolism, thereby promoting plant growth and yield. However, various factors like plant growth stage, doses applied, application method, soil, and environmental conditions may greatly influence their impact on plants. PEs have been reported to enhance salt tolerance in plants primarily through modulation of signaling signatures and pathways (e.g., Na+, ANNA4, GIPC, SOS3, and SCaBP8 Ca2+ sensors, etc.), and regulation of redox machinery [e.g., superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), non-specific peroxidase (POX), glutathione peroxidase (GPX), peroxiredoxin (Prx), ascorbic acid (AsA), glutathione (GSH), α-tocopherol, etc.]. The current study highlights the role of PEs in terms of their sources, methods of preparation, and mode of action with subsequent physiological changes induced in plants against salinity. However, an explicit mode of action of PEs remains nebulous, which might be explicated utilizing transcriptomics, proteomics, metabolomics, and bioinformatics approaches. Being ecological and economical, PEs might pave the way for ensuring the food security in this challenging era of climate change.

Hydrotime analysis to explore the effect of H2O2−priming in the relationship between water potential (Ψ) and germination rate of Capsicum annuum L. seed under NaCl− and PEG−induced stress

Hydrogen peroxide (H2O2) priming was proved to be effective to boost salt and drought stress tolerance in Capsicum annuum L. Hither, hydrotime (HT) approach, a population−based threshold model−germination dependence on water availability, was introduced to account for the effects of reduced water potential on H2O2−primed seeds in progress toward germination. Pre−optimized H2O2 concentrations (1 and 10 mM for 24 h at 25 °C) were applied. Subsequently, seeds were germinated over a range of water potential (Ψ) (0 to −1.2 MPa) induced by sodium chloride (NaCl) and polyethylene glycol (PEG−6000) at 25 °C. We suggest that H2O2−priming affects differently the three derived items of HT model; induced lower hydrotime constant (θH) thus, revealed more rapid germination particularly evident with PEG, shifted the threshold or base water potential for 50% germination (Ψb(50)) towards a more negative value in NaCl culture, reflected a better salinity tolerance, though, the opposite effect was recorded with PEG, and reduced the standard deviation (σΨb), proved a better uniformity of the germination process for both cultures. Thus, H2O2−priming increased GRg (1/tg) at all Ψ>Ψb(g) which is due to both a lower Ψb(50) and a smaller θH in the primed seeds for NaCl culture and primarily owing to reducing θH with no positive effect on Ψb(50) for PEG culture. A normalized time−scale, for comparing responses, was introduced and confirmed the aforementioned impact. Therefore, the crosstalk between H2O2 molecule and different cell pathways generates a constructive response in accordance with imposed stress.

GIBBERELLIC ACID PRIMING ENHANCES MAIZE SEED GERMINATION UNDER LOW WATER POTENTIAL

<p class="abstrakinggris"><span lang="EN-US">Germination is a portentous yield determining factor that is a challenge in the low water potential environment due to disrupted imbibition. Hormonal seed priming can markedly increase the germination on maize even in such a stressful environment. Therefore, research was aimed to analyze the application of gibberellic acid (GA<sub>3</sub>) priming to maize seeds to minimize the deleterious effects of reduced water potential. GA<sub>3</sub> priming was done at 0, 50, 100, 150, and 200 ppm for 12 hours and subjected to drought levels of 0, 0.15, 0.50, 1.05, and 1.75 MPa by using NaCl solution. Different germination parameters, i.e., germination percentage, mean germination time, germination index, relative water content, seedling vigor index, root length, and shoot length, were determined on the final day of the experiment. The results showed that all germination parameters were adversely influenced by low water potential. Every level of GA<sub>3</sub> priming has hastened all parameters. GA<sub>3</sub> priming at 100 ppm decreased the mean germination time by 35 hours under 1.75 MPa compared to non-primed seeds. GA<sub>3</sub> priming increased the shoot length of maize seedlings with a shoot length of 2.9 cm in non-primed seedlings compared to 6.4 cm in 200 ppm GA<sub>3</sub> priming under 1.05 MPa. GA<sub>3</sub> priming is the best method for the early establishment of maize seedlings in low water potential conditions. As a result, it may be utilized as a low-cost and straightforward approach for establishing maize crops under saline and drought conditions.</span></p>

Sodium nitroprusside application enhances drought tolerance in marjoram herb by promoting chlorophyll biosynthesis and enhancing osmotic adjustment capacity

Sodium nitroprusside (SNP) has a decisive function for mitigating water deficit; nevertheless, the specific roles of SNP on chlorophyll biosynthesis, water relation, and osmotic adjustment in marjoram (Origanum marjorana L., Lamiaceae) have not well been established. To assess the function of SNP in alleviating water stress (50% of field capacity), potted marjoram herbs were subjected to watering regimes (well-watered or water-deficit) with or without SNP concentrations (0, 30, 60 μM). Drought caused a significant reduction in water potential (Ψw), osmotic potential (Ψs), turgor potential (Ψp), relative water content (RWC), photosynthetic pigment, chlorophyllide (chlide)a, chlideb, chlorophyll (chl)a/chlidea, chlb/chlideb, and ions, however increased pheophytina (pheoa), protoporphyrin (Proto), Mg-protoporphyrin (Mg-proto), and protochlorophyllide (pchlide). Conversely, osmotic adjustment (OA) was improved, associated with the hyper-accumulation of osmotic adjustment solutes (OAS) leading to an increase in water saturation deficit (WSD), which induced a decrease in dry matter accumulation and shoot fresh weight. Application of SNP decreased Ψw, Ψs, and Ψp and WSD while maintained higher RWC, comparing the plants devoid of SNP supplementation. Supplementary SNP additionally motivated the energetic buildup of various OAO in drought-affected plants that improved OA aptitude, improved water retention capacity, and increased plant growth. Additionally, SNP application increased chlorophyll, carotenoid, pheoa, chlidea, chlideb, chla/chlidea, chlb/chlideb, and decreased Proto, Mg-proto, pchlide, and ions. The findings of the present study clarified that the SNP application improved drought tolerance of marjoram plants, through maintaining ion homeostasis, enhanced OA capacity, increased OAO accumulation, and stabilized chlorophyll biosynthesis.

SHORT-ROOT1 is critical to cell division and tracheary element development in rice roots.

The exocyst is a key factor in vesicle transport and is involved in cell secretion, cell growth, cell division and other cytological processes in eukaryotes. EXO70 is the key exocyst subunit. We obtained a gene, SHORT-ROOT1 (SR1), through map-based cloning and genetic complementation. SR1 is a conserved protein with an EXO70 domain in plants. SR1 mutation affected the whole root-development process: producing shorter radicles, adventitious roots and lateral roots, and demonstrating abnormal xylem development, resulting in dwarfing and reduced water potential and moisture content. SR1 was largely expressed in the roots, but only in developing root meristems and tracheary elements. The shortness of the sr1 mutant roots was caused by the presence of fewer meristem cells. The insitu histone H4 expression patterns confirmed that cell proliferation during root development was impaired. Tracheary element dysplasia was caused by marked decreases in the inner diameters of and distances between the perforations of adjacent tracheary elements. The membrane transport of sr1 mutants was blocked, affecting cell division in the root apical region and the development of root tracheary elements. The study of SR1 will deepen our understanding of the function of EXO70 genes in Oryza sativa (rice) and guide future studies on the molecular mechanisms involved in plant root development.

Comparative metabolomic analysis of the metabolism pathways under drought stress in alfalfa leaves

Alfalfa (Medicago sativa L.) is a very important forage that is severely threatened by water deficiency. Metabolomic changes under drought stress conditions are largely unknown in alfalfa. Therefore, two alfalfa (Medicago sativa L.) cultivars with contrasting tolerance to drought, namely the drought-tolerant Dryland “DT” and drought-sensitive WL343HQ “DS”, were investigated to identify metabolic responses to drought stress. Both the tolerant and sensitive alfalfa showed significant differences in physiological levels under water-limiting conditions. The drought-tolerant cultivar DT sustained growth despite reduced water potential and photosynthesis, suggesting that the functioning of distinct metabolic pathways contributed to enhance tolerance. There were more differentially expressed metabolites produced by DT compared to DS under drought conditions. In addition, the drought-tolerant DT cultivar accumulated more tryptophanol, homocarnosine, S-adenosylhomocysteine, cytidine and clairol, which may be important metabolites for alfalfa drought tolerance. In addition, 17-Hydroxymethylethisterone with unknown function was a candidate tolerance metabolite, whereas the drought-sensitive cultivar DS produced reduced levels of lipid metabolites and increased levels of biosynthesis of amino acids. Among them, the up-regulated l-Proline, l-Arginine and l-Leucine were evident, supporting the conclusion that DS suffered more severe drought stress. This study provided new insights into the metabolic changes of alfalfa in drought stress conditions.

Anisohydric sugar beet rapidly responds to light to optimize leaf water use efficiency utilizing numerous small stomata.

Under conditions of high transpiration and low soil water availability, the demand for water can exceed supply causing a reduction in water potential and a loss of cell turgor (wilting). Regulation of stomatal aperture mediates the loss of water vapour (gs), which in turn is dependent in part on the anatomical characteristics of stomatal density (SD) and stomatal size (SS). Anisohydric sugar beet (Beta vulgaris) is atypical, exhibiting wilting under high soil water availability. Spinach (Spinacia oleracea) belongs to the same family Chenopodiaceae s.s., but demonstrates a more typical wilting response. To investigate the role of stomatal dynamics in such behaviours, sugar beet and spinach leaves were exposed to step-changes in photosynthetic photon flux density (PPFD) from 250 to 2500 µmol m−2 s−1. Using a four log-logistic function, the maximum rate of stomatal opening was estimated. Concurrent measurements of SD and SS were taken for both species. While sugar beet coupled faster opening with smaller, more numerous stomata, spinach showed the converse. After exposure to drought, maximum gs was reduced in sugar beet but still achieved a similar speed of opening. It is concluded that sugar beet stomata respond rapidly to changes in PPFD with a high rate and magnitude of opening under both non-droughted and droughted conditions. Such a response may contribute to wilting, even under high soil water availability, but enables photosynthesis to be better coupled with increasing PPFD.

Germination response of four Arabian desert grasses to low water potential

Species that can germinate under low water potential are likely to have greater utility for fodder production and restoration in arid habitats. We investigated seed germination response of four native grass species (Panicum acuminatum, Panicum turgidum, Pennisetum divisum and Polypogon monspeliensis) to five osmotic potentials (0, −0.3, −0.6, −0.9 and −1.2 MPa) using polyethylene glycol‐6000 and two light treatments (0, 12 h light per day). All the studied species exhibited high germination (> 77%) at ψ = 0 MPa except P. turgidum (42%). Polypogon monspeliensis seeds did not show any significant reduction in germination from ψ = 0 to −0.3 MPa (90–83%), but all other species did, averaging from 75.8 to 60.5%. At ψ = −0.6 MPa seed germination was reduced to around 20%. Germination of most species was unaffected by light, but P. divisum seeds that germinated in darkness were more tolerant to water deficit. Reduction of water potential to −0.3 MPa inhibited the germination timing for P. acuminatum (ca 1.69 days difference to 50% germination [t50]), P. divisum (ca 1.56 day) and P. monspeliensis (ca 1.14 days). Germination of P. acuminatum and P. monspeliensis were similar after stressful exposure to all osmotic potentials, while for P. divisum there was reduced germination (85% at −0.6 MPa to 58% −1.2 MPa), indicating a dormancy induction. Tolerance to low water potentials, and response after release from these low potentials, indicates the species are adapted to survive in drier environments.

Characterization of Exogenous Nitric Oxide Effect on Crocus sativus Response to Different Irrigation Regimes

Water scarcity is one of the main factors limiting crop production worldwide. The study on response of saffron to irrigation regime showed that one-time irrigation at field capacity of 100% resulted in the greatest number and weight of flower, and dry stigma yield, but weekly irrigation regime at the same conditions prevented flowering process. One-time irrigation regime reduced water potential (Ψw) of plants, while the contents of chlorophylls, carotenoid, anthocyanin, carbohydrates, phenol, amino acid, proline, H2O2, and the activity of antioxidant enzymes in the one-time irrigated plants were higher than in the weekly irrigated plants. The nitric oxide (NO) donor, sodium nitroprusside (SNP), significantly increased photosynthetic and non-photosynthetic pigments, metabolites, and antioxidants in both irrigation regimes, with the highest content in the one-time irrigated plants. The SNP treatment increased the flower yield in the one-time irrigated plants, but it could not induce flowering in the weekly irrigated plants. Collectively, these results demonstrated the importance of irrigation regime in flower induction in saffron. Even though the exogenous SNP improved the performance of saffron, it could not overcome the importance of irrigation frequency regime on flowering process. Overall, the SNP application accompanied with the one-time irrigation regime provided higher flower yield and improved the physiological performance of saffron plant.

A new halothermal time model describes seed germination responses to salinity across both sub- and supra-optimal temperatures

We quantified the seed germination responses of chicory (Cichorium intybus L.; Asteraceae) to heat, water and salt stresses using hydrothermal time (HTT) and halothermal time (HaloTT) models. We extended the HaloTT model based on NaCl concentration to include supra-optimal temperatures. The HTT and HaloTT models enabled quantitative comparison of the effects of reduced water potentials and increased salinity on germination. Below 30 °C, the median threshold water potential permitting germination estimated by the HTT model (− 0.83 MPa) was higher than that estimated by the HaloTT model (− 1.30 MPa, after converting the median threshold NaCl concentration to osmotic potential). Ion uptake into seeds imbibed in salt solutions accounted for an average osmotic adjustment of 36% in the presence of salt stress compared to seeds imbibed in polyethylene glycol solutions. These thresholds became more positive above 30 °C with a common median ceiling temperature of 43 °C. The HaloTT models developed here accurately described germination responses to NaCl concentrations across all temperatures and incorporated both water potential and osmotic adjustment effects. With respect to seed germination, chicory could be considered as a moderately water stress tolerant species and highly tolerant to salt stress.

Resistance of Fritillaria imperialis to freezing stress through gene expression, osmotic adjustment and antioxidants

Plant survival in response to freezing stress depends on the efficient activation of tolerance mechanisms. Fritillaria imperialis exposure to freezing stress enhanced signalling molecules Ca2+ and H2O2 along with overexpression of Ca2+ signalling proteins (Ca2+ dependent protein kinases, CPK), followed by upregulation of NHX1 (Na+/H+ antiporter), LEA (late embryogenesis abundant proteins) and P5CS (1-pyrroline-5-carboxylate synthetase). Overexpression of OsCNGC6 was responsible for high accumulation Ca2+, Na+ and K+. The NHX1 gene product transported Na+ to vacuoles and increased cytosolic K+ content to re-establish ionic homeostasis under stress conditions. The reduced water potential of leaves was due to high accumulation of osmolytes and ions. No changes were observed in relative water content of leaves, which might be correlated with overexpression of the LEA gene, which protects against dehydration. High accumulation of H2O2 under freezing stress was responsible for activation of antioxidant systems involving SOD, phenols, anthocyanins, catalase and ascorbate peroxidase. Photosynthesis, suppressed in freezing-stressed plants, returned to normal levels after termination of freezing stress. Taken together, our findings suggest that Fritillaria efficiently tolerated freezing stress through induction of signalling mechanisms and overexpression of cold stress-responsive genes, and prevention of cold-induced water stress, oxidative stress and photosynthetic damage.

Storage of short-lived seeds of Inga vera subsp. affinis in osmotic medium

AbstractInga vera subsp. affinis (Fabaceae) is a tree species native to riparian forests in Southeast Brazil and is key for the restoration of deforested areas. The species produce seeds that are highly recalcitrant. Extreme sensitivity to desiccation as well as vivipary are commonly observed in mature seeds, which also tend towards polyembryony. Past research has shown that typical strategies to store seeds are inapplicable to Inga vera as viability is completely lost when seeds are either dried to around 28% water content (wet basis) or stored at 5°C for a few weeks. Here, we examine the feasibility of storing the seeds under hydrated conditions but at reduced water potential. Freshly collected seeds were kept under conventional storage conditions (plastic bags in cold chamber, 5°C) and in polyethylene glycol (PEG) solutions (−1.6 and −2.4 MPa) at 10°C. Seed germination was assessed after various intervals of time, until all seeds had lost viability. Before storage, seeds attained 100% germination and produced an average of 1.8 normal seedlings per seed (due to polyembryony). Storage in PEG at −1.6 MPa maintained 90% germination (radicle protrusion) and one normal seedling per seed on average for more than 200 d. Osmotic storage likely slowed down metabolism within the seed and hence consumption of food reserves. The storage time achieved has practical applications for in situ restoration, but cannot address ex situ germplasm conservation. Extending shelf life for an additional 6 months allows tree nurseries to optimize the production of seedlings so that they can be planted during the wet season.

Impacts on growth, water relations and nutritional composition of basil plants submitted to irrigation with saline and wastewater

The effect of the application of reclaimed water and saline water on physiological parameters in Ocimum basilicum L. plants were studied to evaluate their adaptability to irrigation with saline water, as well as to evaluate the applicability of wastewater as a source for irrigation. Plants of O. basilicum grown under greenhouse conditions were submitted to different irrigation treatments: control (deionized water 3.10–6 dS m−1), deionized water supplemented with 15 mM NaCl (1.70 dS m−1), deionized water supplemented with 30 mM NaCl (2.46 dS m−1) and ozonized reclaimed water (0.709 dS m−1). The results show that reclaimed water did not promote reduction in water potential of leaf. Likewise, growth-related parameters were not affected by the application of this treatment. The analysis of nutrients composition in the vegetal tissues verified a marked effect of the Na + exclusion in the root tissues. It did not happen occurred in the roots with the same proportion as in the foliar tissues. Considering the results, the ozonized reclaimed water (0.709 dS m−1) can be an alternative for irrigation of O. basilicum L., if it is properly managed.

Role of H2O2 on photosynthetic characteristics of soybean genotypes under low water input

Soybean is subjected to abiotic stresses that immensely affect its productivity during its lifespan and threaten food security globally. Recent research recommends that chemical substances could be applied to plants as an alternative to traditional agriculture to better abide abiotic stresses. Hydrogen peroxide (H2O2) is a potential agent that can serve for this purpose. Up to today, responses of exogenous H2O2 on photosynthetic machinery in plants exposed to drought is poorly investigated. Therefore, the effects of exogenous low dose H2O2 on plant chlorophyll fluorescence in two soy bean genotypes (Glycine max L. Merrill), 537 (tolerant) and 520 (susceptible), under drought were evaluated. Drought which we had found significantly reduced water potential of leaves and photosynthetic pigment concentration in two genotypes, did not cause change in Fv/Fm and ΦPSII of tolerant genotype, contrarily subsided qP and ETR values. However, Fv/Fm, ΦPSII, qP and ETR failed in susceptible genotypes under drought. Increases in NPQ were determined under stress in both genotypes. Exogenous H2O2 mitigated the drought-induced impairment in photosystem II efficiency in both genotypes. This data indicates that low dose H2O2 further enhanced the tolerance to drought via regulation of the photochemical process in both genotypes.

Effect of reduced water potential on seed germination of a forest tree: a hydrotime approach

Abstract: Hydrotime (θH) models provide information on seed tolerance to low water potential and time to germination under different conditions. Here it was evaluated the capacity of graphic and probit model to describe germination parameters and germination times (t) in a tropical legume (Peltophorum dubium). Germination tests were conducted under reduced water potentials (polyethylene glycol solutions from 0 to -1.2 MPa) at 25 °C. Regression lines were applied to investigate the relationship between germination rates (1/t) and water potential for different germination percentages (fractions 10, 30, 50 and 70%). Those regressions were used in the graphic model to calculate θH (1/slope) and determine the base water potential (Ψb) as the point which the line intercepts the x-axis (G% = 0). In the probit model, germination percentages were transformed to probit units and plotted against Ψb-values to describe germination response under a single regression line. Values for θH varied from 1.8 to 2.0 MPa day in both models, and Ψb showed a normal distribution, as presupposed by the probit model. Predicted germination times (t10 and t50) mostly fell within observed times, thus showing biological relevance of the models to describe the effects of water potential on seed germination.

Physiological acclimation of a grass species occurs during sustained but not repeated drought events

Climate change is predicted to result in more variable and extreme precipitation regimes, with potentially longer periods between precipitation events. However, the effects of multiple, sequential drought events on ecosystems and potential acclimation, particularly in grasslands, is poorly understood. In this study, we tested if two simulated drought regimes, (i) sustained drought (soil moisture content reduced from 75 to 25 % field capacity over 14 days and maintained for 29 days) and (ii) repeated drought (two cycles of a reduction to 25 % field capacity, reached after 22 days and 15 days, separated by a rewatering event to 75 % field capacity for 5 days), differentially influence fourteen key physiological responses in the model grass species (Brachypodium distachyon). In addition, we aimed to determine whether plants may acclimate differently to sustained and/or repeated drought events. B. distachyon exhibited plasticity in response to drought, exhibiting two distinct drought resistance responses to the two watering regimes. Plants exposed to sustained drought exhibited early reductions in photosynthesis, stomatal conductance and water potential (43 %, 42 % and 37 %, respectively). However, plants showed physiological acclimation and recovery in these parameters after an additional 3–21 days, but had a ∼50 % lower shoot biomass than well-watered plants. These data demonstrate a conservative, albeit plastic, response to soil water deficit. In contrast, plants exposed to repeated drought responded opportunistically whereby greater fluctuations in photosynthesis, stomatal conductance and water potential (reductions of up to 62 %, 71 % and 90 %, respectively) were closely related to drought and rewatering events. Since plants exposed to repeated drought had a greater reduction in water potential and faster reductions in relative photosynthesis in the second drought event compared to the initial drought event, this may indicate a lack of acclimation under this drought regime. Our results provide evidence for differential responses of B. distachyon to drought and rewatering events, which are dependent on the drought regime (sustained or repeated) and must be carefully considered when interpreting experimental data.

Directional breeding of high oil content peanut variety Yuhua 9 by in vitro mutagenesis and screening

Leaf water potential of peanut subjected to drought stress is positively related to the oil content of peanut kernels. The aim of this study was to directly screen the high oil mutants of peanut and create the new peanut varieties using hydroxyproline as water potential regulator. In vitro mutagenesis was carried out with the embryonic leaflets of peanut variety Huayu 20 as explants and pingyangmycin as a mutagen added into the somatic embryo formation medium. The formed somatic embryos were successively transferred to somatic embryo germination and selection medium containing 6 mmol/L hydroxyproline (at -2.079 MPa water potential ) to induce regeneration and directionally screen high oil content mutants. After that, these plantlets were grafted and transplanted to the experimental field and 132 high oil mutants with oil content over 55% were obtained from the offspring of regenerated plants. Finally, among them, the oil contents of 27 lines were higher than 58% and of 2 lines were higher than 60%. A new peanut variety Yuhua 9 with high yield and oil content was bred from the regenerated plant progenies combining the pedigree breeding method. The yield was 14.0% higher than that of the control cultivar in the testing new peanut varieties of Liaoning province, and also it has passed the national registration of non-major crop varieties. Yuhua 9 with an oil content of 61.05%, which was 11.55 percentage points higher than that of the parent Huayu 20, was the peanut cultivar with the highest oil content in the world. The result showed that it was an effective way for directional breeding of high oil peanut varieties by means of the three-step technique including in vitro mutagenesis, directional screening by reducing water potential in medium and pedigree selection of regenerated plant progenies.

Improving water use efficiency by changing hydraulic and stomatal characteristics in soybean exposed to drought: the involvement of nitric oxide.

A variety of cellular responses is needed to ensure the plants survival during drought, but little is known about the signaling mechanisms involved in this process. Soybean cultivars (EMBRAPA 48 and BR 16, tolerant and sensitive to drought, respectively) were exposed to the following treatments: control conditions (plants in field capacity), drought (20% of available water in the soil), sodium nitroprusside (SNP) treatment (plants irrigated and treated with 100-µM SNP [SNP-nitric oxide (NO) donor molecule], and Drought + SNP (plants subjected to drought and SNP treatment). Plants remained in these conditions until the reproductive stage and were evaluated for physiological (photosynthetic pigments, chlorophyll a fluorescence and gas exchange rates), hydraulic (water potential, osmotic potential and leaf hydraulic conductivity) and morpho-anatomical traits (biomass, venation density and stomatal characterization). Exposure to water deficit considerably reduced water potential in both cultivars and resulted in decrease in photosynthesis and biomass accumulation. The addition of the NO donor attenuated these damaging effects of water deficit and increased the tolerance index of both cultivars. The results showed that NO was able to reduce plant's water loss, while maintaining their biomass production through alteration in stomatal characteristics, hydraulic conductivity and the biomass distribution pattern. These hydraulic and morpho-anatomical alterations allowed the plants to obtain, transport and lose less water to the atmosphere, even in water deficit conditions.

Multiple abiotic stress, nitrate availability and the growth of wheat

In the field, wheat experiences a combination of physical and nutrient stresses. There has been a tendency to study root impedance and water stress in separation and less is known about how they might interact. In this study, we investigated the effect of root impedance on the growth of three wheat varieties (Cadenza, Xi19 and Battalion) at different levels of nitrate availability, from 0–20 mM nitrate, in sand culture. This model system allows soil strength to be increased while maintaining adequate water availability. In a separate pot experiment, we grew the same wheat varieties in a loamy sand where soil was allowed to dry sufficiently to both reduce water potential and increase root impedance. This pot experiment also had a range of nitrate availabilities 0–20 mM nitrate. Once the seedlings were established we limited water supply to apply a matric potential of approximately −200 kPa to the roots. Soil drying increased the penetrometer resistance from approximately 300 kPa to more than 1 MPa. There were differences between the two experimental systems; growth was smaller in the soil-based experiment compared to the sand culture. However, the effects of the experimental treatment, root impedance or water withholding, relative to the control were comparable. Our data confirmed that leaf elongation in Cadenza (carrying the tall Rht allele) was the most sensitive to root impedance. Leaf stunting occurred irrespective of nitrate availability. Leaf elongation in the Xi19 and Battalion (carrying the semi-dwarf Rht allele) was less sensitive to root impedance and drought than Candenza. We suggest that the critical stress in a pot experiment where the soil was allowed to dry to approximately −200 kPa was root impedance and not water availability.