Published and additional data for polyethylene glycol 8000 (PEG), formerly PEG 6000, solution water potentials (Ψ) are compared. Actual bars Ψ over the concentration range of 0 to 0.8 gram PEG per gram H2O and temperature (T) range of 5 to 40°C are best predicted (probably within ± 5%) by this equation: Ψ = 1.29[PEG]2T − 140[PEG]2 − 4.0[PEG]. Although transformable through division by [PEG] to virial equation form, results indicate that the coefficients are not virial. Mannitol (MAN) interacts with PEG to produce Ψ significantly lower than additive. Vapor pressure osmometer (VPO) data for MAN-PEG synergism compared favorably with those from thermocouple hygrometry; and VPO data showing the interactions between PEG and four salts are presented. The synergism of MAN-PEG and of NaCl-PEG are related linearly to the concentration of solute added with PEG.

Evaluation of the water potentials of solutions of polyethylene glycol 8000 both in the absence and presence of other solutes.

A comprehensive investigation was carried out to determine the changes that occurred in water-stressed cucumber (Cucumis sativus L.) in response to melatonin treatment. We examined the potential roles of melatonin during seed germination and root generation and measured its effect on reactive oxygen species (ROS) levels, antioxidant enzyme activities, and photosynthesis. Melatonin alleviated polyethylene glycol induced inhibition of seed germination, with 100 μm melatonin-treated seeds showing the greatest germination rate. Melatonin stimulated root generation and vitality and increased the root:shoot ratio; therefore, melatonin may have an effect on strengthening cucumber roots. Melatonin treatment significantly reduced chlorophyll degradation. Seedlings treated with 100 μm melatonin clearly showed a higher photosynthetic rate, thus reversing the effect of water stress. Furthermore, the ultrastructure of chloroplasts in water-stressed cucumber leaves was maintained after melatonin treatment. The antioxidant levels and activities of the ROS scavenging enzymes, i.e., superoxide dismutase, peroxidase, and catalase, were also increased by melatonin. These results suggest that the adverse effects of water stress can be minimized by the application of melatonin.

Melatonin promotes water‐stress tolerance, lateral root formation, and seed germination in cucumber (Cucumis sativus L.)

Seed treatments are used on many crop seeds for a variety of purposes. The greatest use of seed treatments has been to provide an inexpensive insurance against rotting of planted seeds by soil fungi such as Pythium spp. and Rhizoctonia solani. Seed treatments for many other purposes are being de­ veloped and used. Increasingly, commercial seed treaters are beginning to view seed treatments as a means to substantially increase the value of the seed and to improve plant growth and productivity. Examples of other types of seed treatments are: (a) treatment with systemic chemicals that can translocate into the seed to control deep-seated plant pathogens. Several chemicals also translocate to the above-ground portions of the seedling and protect against foliar diseases; (b) treatment with microor­ ganisms that can proliferate on the seed, transfer to the root and fix N2, enhance uptake of nutrients, protect the subterranean plant portions against attack by soil-inhabiting fungi, and/or increase plant growth; (c) physical treatments that control seedbome pathogens; (d) seed coatings or pellets that can improve seed shape for planting or provide other benefits; (e) physiolog­ ical seed treatments that enhance germination rate and plant performance; and (j) various treatments that affect seed moistUre relationships and result in improved seed storability or performance.

Concepts and Technologies of Selected Seed Treatments

Drought stress is a major factor in reduce growth, development and production of plants. Stress was applied with polyethylene glycol (PEG) 6000 and water potentials were: zero (control), -0.15 (PEG 10%), -0.49 (PEG 20%), -1.03 (PEG 30%) and -1.76 (PEG40%) MPa. The solutes accumulation of two maize (Zea mays L.) cultivars -704 and 301- were determined after drought stress. In our experiments, a higher amount of soluble sugars and a lower amount of starch were found under stress. Soluble sugars concentration increased (from 1.18 to 1.90 times) in roots and shoots of both varieties when the studied varieties were subjected to drought stress, but starch content were significantly (p<0.05) decreased (from 16 to 84%) in both varieties. This suggests that sugars play an important role in Osmotic Adjustment (OA) in maize. The free proline level also increased (from 1.56 to 3.13 times) in response to drought stress and the increase in 704 var. was higher than 301 var. It seems to proline may play a role in minimizing the damage caused by dehydration. Increase of proline content in shoots was higher than roots, but increase of soluble sugar content and decrease of starch content in roots was higher than shoots.

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Drought-induced Accumulation of Soluble Sugars and Proline in Two Maize Varieties

Osmotic pressures (II) of aqueous solutions of polyethylene glycols (PEGs) of average relative molecular weight (M(r)) between 200 and 10,000 were measured using vapor pressure deficit osmometry. The relationships between molarity and II were described with high precision by second order polynomials for each of the PEGs studied. In contrast to previous reports, equivalent weights of different polymers in solution did not generate the same II; low M(r) PEGs generated a higher II than the higher M(r) PEGs. The effect of PEGs upon II represents an interaction between concentration and M(r).

Osmotic Pressure of Aqueous Polyethylene Glycols : Relationship between Molecular Weight and Vapor Pressure Deficit.

Water potential (Psiomega) values were determined for aqueous colloids of four molecular sizes of polyethylene glycol (PEG) using freezing-point depression and vapor-pressure deficit methods. A significant third-order interaction exists between the method used to determine Psiomega, PEG molecular size, and concentration. At low PEG concentrations, freezing-point depression measurements result in higher (less negative) values for Psiomega than do vapor-pressure deficit measurements. The reverse is true at high concentrations. PEG in water does not behave according to van't Hoff's law. Psiomega is related to molality for a given PEG but not linearly. Moreover, Psiomega varies with the molecular size of the PEG. It is suggested that the Psiomega of PEG in water may be controlled primarily by the matric forces of ethylene oxide subunits of the PEG polymer. The term matricum is proposed for PEG in soil-plant-water relation studies.

/pdf/water-potential-of-aqueous-polyethylene-glycol-4p69arwhi6.pdf

Joe R. Goodin

Papers

Water Potential of Aqueous Polyethylene Glycol