Osmotic potential (it.) of aqueous solutions of polyethylene glycol 6000 (PEG-6000) was curvilinearly related to concentration. At given concentrations, AI. increased linearly with temperature. The effects of concentration and temperature on ,1. of PEG-6000 solutions differ from those for most salts and sugars and apparently are related to structural changes in the PEG polymer. Measurements of t'. with thermocouple psychrometers are more negative than those with a vapor pressure osmometer, with the psychrometer probably giving the more nearly correct i1, for bulk solutions. An empirical equation permits calculation of A1, from known concentrations of PEG-6000 over a temperature range of 15 to 35 C. Viscometery and gravimetric analysis are convenient methods by which the concentrations of PEG-6000 solutions may be measured.The use of polyethylene glycol to adjust osmotic potential (s,) requires accurate knowledge of the effect of PEG2 on if. The calculation of i, from freezing point depression is unsatisfactory (9). Thermocouple psychrometry (9,11,13,(19)(20)(21) and vapor pressure osmometry (7,12,17) have been employed; however concentrations used to achieve f, values frequently have not been given (7,(11)(12)(13)(14)17) or were reported graphically (4,9,(19)(20)(21)

ABSTRACrPdsahd aW additiona data for e glycol O0 (PEG),formerly PEG 6000, s o water potentals (9) are cm e Actual bs 9 oa the c rup of 0 to 08 grm PEG per grm H20and tpere (7) (5). That either approach is better statistically was not apparent (5) so both forms were used for each data set. All analyses were by the GLM procedure of SAS. Parameters with coefficients not significantly different from zero were eliminated and the new model analyzed.RESULTS AND DISCUSSION PEG Aloe. Most available measurements of 9 for PEG solutions have been made at or below 0.4 g PEG/g H20 and at 25°C. The points in Figure I represent

Data required to prepare solutions with desired solute potentials at any temperature from 0 to 40°C are scattered, often have inappropriate units, and usually require involved calculation or are not available. We wished to prepare a program so that anyone could obtain pertinent information simply. Adequate published data could be found only for mannitol, PEG 8000, NaCl, KCl, and sucrose, with water displacement by mannitol and PEG 8000 having to be measured. The program sends tabular output to the screen and it may be written in a disk file, making observation of relationships and preparation of graphical representation simple. A sequence of data may be generated over temperature, concentration, or potential ranges by specifying an initial value, interval size, and number of intervals. Values are given for temperature, water density, molal and molar concentrations, g solute g−1 water, osmotic coefficient, g and mL water displaced g−1 solute, solute potential (MPa), and g solute and g water needed for a requested volume of solution.

Summary. Cotton plants, Gossypiunt hirsutum L. were grown in a growth room under incident radiation levels of 65, 35, and 17 Langleys per hour to determine the effects of vapor pressure deficits (VPD's) of 2, 9, and 17 mm Hg at high soil water potential, and the effects of decreasing soil water potential and reirrigation on transpiration, leaf temperatture, stomatal activity, photosynthesis, and respiration at a VPD of 9 mm Hg.Transpiration was positively correlated with radiation level, air VPD and soil water potential. Reirrigation following stress led to slow recovery, which may be related to root damage occurring during stress. Leaf water potential decreased with, but not as fast as, soil water potential.Leaf temperature was usually positively correlated with light intensity and negatively correlated with transpiration, air VPD, and soil water. At high soil water, leaf temperatures ranged from a fraction of 1 to a few degrees above ambient, except at medium and low light and a VPD of 19 mm Hg when they were slightly below ambient, probably because of increased transpirational cooling. During low soil water leaf temperatures as high as 3.4°above ambient were recorded. Reirrigation reduced leaf temperature before appreciably increasing transpiration. The upper leaf surface tended to be warmer than the lower at the beginning of the day and when soil water was adequate; otherwise there was little difference or the lower surface was warmer. This pattern seemed to reflect transpiration cooling and leaf position effects.Although stomata were more numerous in the lower than the upper epidermis, most of the time a greater percentage of the upper were open. With sufficient soil water present, stomata opened with light and closed with darkness. Fewer stomata opened under low than high light intensity and under even moderate, as compared with high soil water. It required several days following reirrigation for stomata to regain original activity levels.Apparent photosynthesis of cotton leaves occasionally oscillated with variable amplittude and freqtlency. When soil water was adequate, photosynthesis was nearly proportional to light intensity, with some indication of higher rates at higher VPD's. As soil water decreased, photosynthesis first increased and then markedly decreased. Following reirrigation, photosynthesis rapidly recovered.Respiration was slowed moderately by decreasing soil water but increased before watering. Respiration slowed with increasing leaf age only oIn leaves that were previously tinder high light intensity.Mlost micrometeorological studies presently deal lems involved has been presented by Collis-George xvith changes in the whole or segments of pastures, (11). With the foregoing in mind, these stuidies rangelands, forests, or ctultivated crops. In any of patterned after earlier stuidies on corn (29)

Two cultivars of soybean (Glycine max [L.] Merr.) were grown in solution with up to 100 millimolar NaCl. Leaf solute potential was -1.1 to -1.2 megapascals in both cultivars without NaCl. At 100 millimolar NaCI leaf solute potential was -3.1 to -3.5 megapascals in Bragg and -1.7 megapascals in Ransom. The decrease in solute potential was essentially proportional to the concentration of NaCl. In both salt susceptible Bragg and salt semitolerant Ransom, leaf proline was no more than 0.4 micromole per gram fresh weight at or below 20 millimolar NaCI. At 40 and 60 millimolar NaCI, Bragg leaf proline levels were near 1.2 and 1.9 micromoles per gram fresh weight, respectively. Proline did not exceed 0.5 micromole per gram fresh weight in Ransom even at 100 millimolar NaCI. Proline accumulated in Bragg only after stress was severe enough to induce injury; therefore proline accumulation is not a sensitive indicator of salt stress in soybean plants.With the solute potential of a nutrient solution (about -0.07 MPa) being decreased nearly 0.05 MPa for each 10 mm increase in NaCI, leaves of plants growing in solutions with added NaCl would be expected to respond with lower solute potentials (6,10 soybean for up to 7 d exposure to one concentration (75 mM) of NaCl in solution culture. They also measured plant transpiration and the Cl-, Na', ABA, and cytokinin contents of plant parts.The present study was undertaken to clarify the relationships among salt tolerance, leaf solute potential, and the capacity to accumulate proline in two cultivars of soybean, salt sensitive Bragg and salt semitolerant Ransom. Our results will be compared with those of Roeb et al. Treatments. After 7 d in jars, salinity treatments were begun by adding NaCl to the basal nutrient solution. Three levels, 0, 10, and 100 mM constituted a first experiment. Stepwise additions were used to reach 100 mM with reduced osmotic shock. The first two steps were 10 mM d-'; others were 20 mm d-'. Each treatment was replicated six times. Plants were randomly distributed, with positions changed daily. The third (mature) and sixth (young) leaves, counting from the first trifoliate leaf, were harvested 14 d after beginning treatment. Because of results obtained, 0 and intermediate levels of 20, 40, and 60 mm NaCl were used in a second experiment. The only other difference was that all steps were 20 mM d-'. Plants were exposed to final levels of 10, 20, 40, 60, or

ABSTRACIA practal gude to cutg the manItol (MAN) am t requred to achieve the daeied water potential (') of polyethy glycoV dextran (PEG/DEX) queous two-hase systems for prot t purifcati s prnted he lem l generated equati 9 -305IPEGI21MANI + 0.741PEG1IMANI Aqueous two-phase polymer systems for partitioning biological materials were introduced more than two decades ago (1, and references therein). Purification of cells, organelles, and macromolecules using these systems has gained wide acceptance. The most commonly used system is formed when polyethylene glycol and dextran are dissolved in water. Above certain critical concentrations (4), an upper PEG2-rich phase and a lower DEX-rich phase separate. Biological materials fractionate into one of these phases or collect at the interface depending on density and on hydrophobic and/or electrical properties of the particles. Ions enhance electrical phenomena. Some ions (e.g. HP042-) distribute asymmetrically between the phases (6) creating a modest potential (e.g. 7). In 1973, Kanai and Edwards (8)

No abstract

totropically inactive green light was used as necessary. On the 5th day a 10-mm section was cut from each hypocotyl, beginning 2 mm below the top of the hook.Sections to be stirred were cut into an empty dish before being transferred into a 50-ml Erlenmeyer flask containing 20 ml of water or solution. The flask was stoppered and clamped in a horizontal position to a vertical wheel, which was rotated at 12 rpm.Sections to be held in saturated air were cut onto plastic screening placed over wet filter paper in the bottom of a small Petri dish and covered with a lid lined with wet filter paper. The small dish was placed inside a larger one.Growth regulator solutions, with GA7 substituted for GA., contained ,/M IAA, 0.1 mm GA7, 0.1 mi CoCl,, and 10 mM KCl (10). Length differences were tested for significance as indicated previously (10).An earlier report (10) indicated that elongation of cucumber hypocotyl sections in growth regulator solution was suppressed more by Carbowax 6000 than by mannitol at equivalent water potentials. Carbowax 6000 and mannitol reduced respiration comparably. Pretreatment with mannitol reduced subsequent growth more than pretreatment with Carbowax 6000. Packer (12) extended comparisons between mannitol and Carbowax 6000. She suggested, but did not show, that boundary layers might cause the differences in elongation noted for mannitol and Carbowax solutions at equivalent water potentials. She also reported extensive data confirming more rapid deterioration of sections in mannitol than in isotonic Carbowax.In the work reported here, growth media containing osmotica were stirred to determine whether reduction of boundary layers would largely eliminate differences in growth responses to the two osmotica. The observation of different shrinkage in hypertonic Carbowax from that in hypertonic mannitol stimulated additional experimentation directed toward explaining this difference. During exposure to any osmoticum, deterioration of the ability of sections to elongate might reflect side effects rather than water potential effects of the osmoticum; therefore, a means of suppressing growth without introducing osmotica, inhibitors, anaerobic conditions, or lowered temperature was sought. Suppressing growth by holding sections in saturated air was chosen as a standard for comparison in estimating possible deleterious effects of exposure to Carbowax and mannitol. MATERIALS AND METHODSAsgrow Vigorpak cucumber (Cucumis sativus L. Marketer) seedlings were grown in sand in a 25 C darkroom. Pho- RESULTSIn growth regulator solution, stirring largely eliminated the differences between Carbowax and mannitol (Fig. 1); however, the small differences at -4, -5, -6, -8, -9, and -10 bars were significant at the 1% level. In the absence of growth regulators, stirring eliminated differences except at potentials below -6 bars (Fig. 2). Hypertonic solutions of mannitol caused greater length reductions than comparable solutions of Carbowax 6000.Stirring, itself, affected elongation. Comparison of previous results (10) wi...