osmotic potential
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Abstract The genetic potentials of eight species of Achillea (A. millefolium, A. fillipendulla, A. biebersteinii, A. nobilis, A. eriophora), Matricaria (M. ricotita), and Anthemis (An. haussknechtii and An. tinctoria) under drought conditions during the seedling stage were measured. Non-ionic water-soluble polymer polyethylene glycol (PEG, molecular weight 6000) was used to simulate water stress at five osmotic potential levels (0, –0.3, –0.6, –0.9, and –1.2 MPa). An acceptable threshold value for germination was osmotic potential –0.6 MPa, and the modest osmotic potential was –1.2 MPa for studied taxa. Seedlings of germinated at two control and osmotic potential –0.6 MPa (as an acceptable threshold value for germination) treatments were sowed in a field under rainfed conditions. Genetic differentiation of control plants (CP) versus early selected plants (ESP, germinated at osmotic potential –0.6 MPa) was studied using morphological, physiological, and molecular (ISSR) markers. No significant differences were observed between morphological traits of CP and ESP in all species, however, days to full flowering shortened in ESP. The physiological results demonstrate that under rainfed conditions, the ESP, in a quick response, collect osmolytes and amplify the activity of antioxidative enzymes to survive drought. The genetic relationship in the group of genotypes, that ISSR marker set it out, is affiliated to taxon even though AMOVA showed a partial differentiation between CP and ESP groups (21%). It was concluded that the selection of tolerating individuals at the seedling stage represents a likely positive strategy to have higher drought tolerance feature in plants under rainfed conditions.

The success of mine site restoration programs in arid and semi-arid areas poses a significant challenge and requires the use of high-quality seedlings capable of tolerating heavy metal stresses. The effect of ectomycorrhizal fungi on different physiological traits was investigated in Pinus halepensis seedlings grown in soil contaminated with heavy metals (Pb-Zn-Cd). Ectomycorrhizal (M) and non-ectomycorrhizal (NM) seedlings were subjected to heavy metals stress (C: contaminated, NC: control or non-contaminated) soils conditions for 12 months. Gas exchange, chlorophyll fluorescence, water relations parameters derived from pressure–volume curves and electrolyte leakage were evaluated at 4, 8 and 12 months. Ectomycorrhizal symbiosis promoted stronger resistance to heavy metals and improved gas exchange parameters and water-use efficiency compared to the non-ectomycorrhizal seedlings. The decrease in leaf osmotic potentials (Ψπ100: osmotic potential at saturation and Ψπ0: osmotic potential with loss of turgor) was higher for M-C seedling than NM-C ones, indicating that the ectomycorrhizal symbiosis promotes cellular osmotic adjustment and protects leaf membrane cell against leakage induced by Pb, Zn and Cd. Our results suggest that the use of ectomycorrhizal symbiosis is among the promising practices to improve the morphophysiological quality of seedlings produced in forest nurseries, their performance and their tolerance to multi-heavy metal stresses.

Conyza sumatrensis (Retz.) E. H. Walker is an obnoxious weed, emerging as an invasive species globally. Seed germination biology of four populations of the species stemming from arid, semi-arid, temperate, and humid regions was determined in this study. Seed germination was recorded under six different environmental cues (i.e., light/dark periods, constant and alternating day and night temperatures, pH, salinity, and osmotic potential levels) in separate experiment for each cue. Populations were main factor, whereas levels of each environmental cue were considered as sub-factor. The impact of seed burial depths on seedling emergence was inferred in a greenhouse pot experiment. Seed germination was recorded daily and four germination indices, i.e., seed germination percentage, mean germination time, time to reach 50% germination, and mean daily germination were computed. Tested populations and levels of different environmental cues had significant impact on various seed germination indices. Overall, seeds stemming from arid and semi-arid regions had higher seed germination potential under stressful and benign environmental conditions compared to temperate and humid populations. Seed of all populations required a definite light period for germination and 12 hours alternating light and dark period resulted in the highest seed germination. Seed germination of all populations occurred under 5–30°C constant and all tested alternate day and night temperatures. However, the highest seed germination was recorded under 20°C. Seeds of arid and semi-arid populations exhibited higher germination under increased temperature, salinity and osmotic potential levels indicating that maternal environment strongly affected germination traits of the tested populations. The highest seed germination of the tested populations was noted under neutral pH, while higher and lower pH than neutral had negative impact on seed germination. Arid and semi-arid populations exhibited higher seed germination under increased pH compared to temperate and humid populations. Seed burial depth had a significant effect on the seedling emergence of all tested populations. An initial increase was noted in seedling emergence percentage with increasing soil depth. However, a steep decline was recorded after 2 cm seed burial depth. These results indicate that maternal environment strongly mediates germination traits of different populations. Lower emergence from >4 cm seed burial depth warrants that deep burial of seeds and subsequent zero or minimum soil disturbance could aid the management of the species in agricultural habitats. However, management strategies should be developed for other habitats to halt the spread of the species.

AbstractBelonging to the Brazilian flora, the species Hancornia speciosa (Gomes), known as mangabeira, has bioactive compounds of interest, such as flavonoids, xanthones, and proanthocyanidins. The objective of this study was to determine how the supplementation of sugars in culture medium affects the osmotic potential of the medium, as well as its influence on cell growth and on the concentration of phenolic compounds. For this purpose, after 90 days of subculture, 20 mL aliquots of the cultures were added to flasks containing 20 mL of medium with different sugars (glucose, fructose, sucrose, mannitol, and sorbitol) under a 16-h photoperiod with a spectral range between 400 and 700 nm of photosynthetically active radiation (45–55 μmol m−2 s−1) in a shaker at 110 rpm. After 30 days, the pH, electrical conductivity, osmotic potential, biomass accumulation, and concentrations of phenolic compounds were evaluated. Regardless of their concentration in the medium, the sugars sorbitol and mannitol provided more unfavorable conditions for water absorption at the cellular level, reducing the water potential of the medium. Sucrose favored greater water absorption and biomass accumulation. Among the various sugar concentrations, 3% (30 g/L) sucrose or glucose improved the accumulation of fresh and dry cell weight and the production of polyphenols such as chlorogenic acid, epicatechin, rosmarinic acid, hesperidin, rutin, and quercetin. In addition, they resulted in a higher osmotic potential of the medium and larger cells than other carbon sources. Despite the differences in cell size, no culture conditions compromised cell survival.

This work deals with the assessment of physiological and biochemical responses to salt stress, as well as the regulation of the expression of the K+/Na+ transporter gene-TaHKT1;5 of two Triticum aestivum L. genotypes with contrasting tolerance. According to the observations, salinity stress caused lipid peroxidation; accumulation of soluble sugars and proline; decreased osmotic potential, Fv/Fm value, and K+/Na+ ratio; and increased the activity of antioxidant enzymes in both genotypes. In the salt-tolerant genotype, the activity of enzymes, the amounts of soluble sugars and proline were higher, the osmotic potential and the lipid peroxidation were lower than in the sensitive one, and the Fv/Fm value remained unchanged. A comparison of the accumulation of Na+ and K+ ions in the roots and leaves showed that the Na+ content in the leaves is lower. The selective transport of K+ ions from roots to leaves was more efficient in the salt-tolerant genotype Mirbashir-128; consequently, the K+/Na+ ratio in the leaves and roots of this genotype was higher compared with the sensitive Fatima genotype. The semi-quantitative RT-PCR expression experiments on TaHKT1;5 indicated that this gene was not expressed in the leaf of the wheat genotypes. Under salt stress, the expression level of the TaHKT1;5 gene increased in the root tissues of the salt-sensitive genotype, while it decreased in the salt-tolerant wheat genotype. The results obtained suggest that the ion status and salt tolerance of the wheat genotypes are related to the TaHKT1;5 gene activity.

Aims: The aim of this study was to investigate the effect of iso-osmotic potentials of drought and salinity on physiological parameters of grass pea seedlingsas well as to compare varietal responses. Study Design: Completely randomized design. Place and Duration of Study: In the years 2017-2018 and 2018-2019, laboratory research on grass pea varieties BK-14 and Pratik was conducted in the Department of Plant Physiology, Bidhan Chandra Krishi Viswavidyalaya, Nadia, West Bengal, India. Methodology: The effect of iso-osmotic potential of salinity and drought stress was studied using NaCl (50, 100 and 200 mM ) and PEG 6000 (10, 12 and 18%) solutions with -0.2, -0.4, and -0.8 MPa osmotic potential, and the experiment was carried out in sand culture using modified Hoagland solution under diffused light, at about 80±1% relative humidity (R.H.) and a temperature of 22±1oC. Data on different physiological and biochemical parameters were recorded after ten days of seedling growth in sand culture. Statistical analysis was performed on the mean data in all cases following completely randomized design (CRD) by application of INDOSTAT version 7.1 software. Results: The germination of grass pea seeds was more severely affected by drought stress than salinity. Both stresses had a negative impact on most of the parameters studied except for leaf proline and sugar The impact became  more pronounced as the severity of the stress increased. The highest intensity of drought stress was found to be more detrimental to leaf protein and relative water content in BK 14, while Pratik was more drastically affected by the highest level of salinity. Drought was found to have a significant negative impact on leaf starch in both the grass pea varieties. The highest concentration of PEG led to a remarkable increase in leaf proline. Conclusion: The mild to moderate levels (-0.2 and -0.4 MPa)  of stress did not produce much severe effects on the grass pea seedlings, but the highest intensity of stress with an osmotic potential of -0.8 MPa mostly produced drastic effects. There were varietal differences in response to two abiotic stresses. In general, drought stress was found to cause more negative effects on seedling than iso-osmotic potential of salinity stress.

Background: Salinity and drought are the major abiotic stresses and both can cause osmotic imbalances. Drought stress directly results in osmotic stress whereas salinity problem firstly disrupts the water balance and eventually induces ion toxicity which results in cyto-toxicity, metabolic impairment, nutrient imbalance and finally poor crop growth and yield. The co-ordinated up-regulation or constitutive expression of antioxidative system in plants is the main defense in plant against these stresses and thus the present experiment was undertaken to study the antioxidant responses under drought and salinity stress at seedling stage in ricebean (Bidhan 1). Methods: For studying the effect of iso-osmotic potential of salinity and drought stress solutions of NaCl and PEG 6000 with -0.2 MPa (50mM NaCl and 10% PEG), -0.4 MPa (100 mM NaCl and 12% PEG) and -0.8 MPa (200mM NaCl and 18% PEG) osmotic potential were used. The experiment was done in the laboratory of Department Plant Physiology, Bidhan Chandra Krishi Viswavidyalaya (BCKV), Mohanpur, Nadia and West Bengal in the year 2017-18 and 2018-19. Result: Under moderate to high intensity of osmotic stresses the leaf proline content decreased. The mild and medium stress treatments induced much higher activity of GPOX and APX in the leaf which then decreased somewhat as the intensity of stress increased. The experiment showed that drought stress was found to produce more drastic effects on seedling growth in ricebean as compared to the salinity stress at iso-osmotic potentials.