Abstract
Seedlings of Lolium multiflorum Lam., Lespedeza stipulacea Maxim., and Buteloua curtipendula (Michx.) Torr. were grown for 48 hours in darkness at constant temperatures of 22°, 27°, 32°, or 37°C either in distilled water or polyethylene glycol 20,000 (PEG) solutions with osmotic potentials of −3.2, −7.7, and −9.8 bars. Redicle growth rate decreased as concentrations of polyethylene glycol increased. Radicle growth was reduced at 32° and negligible at 37° for L. multiflorum. All levels of PEG-induced osmotic stress reduced radicle growth at 22° and 32°, while at 27° only higher levels reduced growth of L. multiflorum. PEG-induced osmotic stress reduced radicle growth of B. curtipendula significantly at all temperatures except 37°, where the lowest level of PEG had an insignificant effect on radicle growth. With L. stipulacea, low levels of PEG-induced osmotic stress did not have a significant effect on radicle growth, but an osmotic stress of −9 bars reduced growth at all temperatures.
( Deng et al., 2014 ). The treatment methods of the samples described above were as follows: ‘Cabernet Sauvignon’ ( V. vinifera ) plants were treated with 120-m m salt [NaCl:CaCl, v/v (10:1)], polyethylene glycol (PEG), cold (5 °C), or unstressed
Abstract
Apple seedlings (Malus domestica Borkh.) were grown in the greenhouse under a range of polyethylene glycol (PEG)-induced osmotic potential stresses up to −7.5 bars. Water use by seedlings (ml water consumed/dm2 leaf area) responded to ambient temperature fluctuations after 4 days in the solution. During the first 4 days after initiation of the stress, no response was obtained indicating that the seedlings were undergoing an “adaptation period.” Plants receiving higher osmotic stresses were less able to respond to ambient temperature fluctuations as measured by transpiration. Transpiration rate decreased as osmotic stress was increased. PEG-induced osmotic water stress and water stress in soil were compared, the latter by letting the soil mass dry out. Comparable transpiration rates from the 2 methods, when plotted, showed that PEG-induced osmotic stresses of −0.5 and −4.0 bar were equivalent to greenhouse potting soil at 75% of field capacity and approaching the wilting point, respectively. It was concluded that the PEG-induced water stress was similar to water stress in soil, thus PEG-induced stress can be used in experiments with apples to study various effects of water stress. Use of a freezing point depression osmometer in determining solution osmotic potentials of PEG-modified solutions is described.
in ‘Summit’ sweet cherry fruit. Microcracks were induced by incubating fruit for 24 h in isotonic PEG 6000 solution. Tonicity was established by water vapor pressure osmometry (VAPRO ® 5520 and 5600; Wescor, Logan, UT) of juice extracted from fruit
Grape cv. Valiant was micropropagated in an MS medium with and without 2% (W/V) of polyethylene glycol (PEG, MW 8000). Leaf anatomy of control (in vitro, no PEG), treated (in vitro, PEG), field grown and greenhouse grown plants were compared under light microscopy. Cell size, palisade layer formation, relative intercellular air space and apparent chloroplast number varied between the leaves of control and PEG treated (high osmoticum) plantlets. These leaf characteristics in the high osmoticum medium appeared more similar to the leaves of the greenhouse and field grown plants. Leaves from control plantlets contained cells of larger size, lacked normal palisade layer formation, greater intercellular pore spaces and fewer chloroplasts. Leaves of PEG treated plantlets had smaller cells, a more defined palisade layer, reduced intercellular pore spaces and greater number of chloroplasts. Leaves of greenhouse and field grown plants had small cells, a well-defined palisade layer, least intercellular pore space and greatest number of chloroplasts. These results demonstrate that a high osmoticum medium may be used to induce more normal leaf development.
Polyethylene glycol (PEG) was evaluated for its influence on hardening of in vitro-propagated `Fern' strawberries (Fragaria ×ananassa) when applied just before transplanting. Strawberries were micropropagated via shoot tips and grown in vitro until roots were well developed. Plantlets were then transferred onto filter paper bridges in liquid medium with 15% (w/v) of PEG-8000. After treatment in the medium for various periods, the plants were compared to the control (no PEG) for water loss from detached leaves, stomatal aperture, and survival rates after transplanting. Leaf epicuticular wax was also quantified. Overall, the in vitro PEG treatment was not successful in significantly increasing hardiness and survivability of the strawberry plants after transplanting from in vitro conditions to a soil medium. Osmotic stress was created, but apparently not for the time needed to increase survival. Further tests are needed to pinpoint the proper exposure time required to increase hardiness and survivability after transplanting plantlets. To increase survival, the time exposed to PEG should be 15, 18, or possibly 21 days.
Detached and intact leaves (first fully expanded leaf from the top) of tobacco (Nicotiana tabaccum L.) plantlets hardened in vitro with 2.0% polyethylene glycol (PEG) showed increased diffusive resistance (r) over those of nonhardened plantlets as measured by a steady state porometer. The leaves of the PEG hardened plants maintained a higher resistance throughout the one hour dessication period in approximately 30% relative humidity although both treatments showed an increase in diffusive resistance after 30 minutes. This indicates that the stomates are functioning in the in vitro tobacco plantlets. The higher (r) in the PEG treated plants may be due to more complete closure of stomates, higher cuticle wax content or a combination of both.
Transient expression of electroporation-mediated DNA uptake was monitored in callus-derived protoplasts of two asparagus (Asparagus offcinalis L.) genotypes by measuring the GUS activity. The level of expression and the viability of the protoplasts were influenced by the voltage and duration of the electric pulse. An increased plasmid DNA concentration and the presence of polyethylene glycol (PEG) in the electroporation medium enhanced the transient expression level. A considerable increase in GUS activity was observed in the presence of both PEG and heat-shock treatments than with PEG treatment alone. An optimal level of GUS activity was obtained after electroporation with a capacitive discharge of 500 V/cm and 94 ms duration. The two genotypes differed in their responses in vitro and also showed variable levels of transient expression. The present technique was suitable to obtain transgenic plants, as histochemical GUS assay revealed GUS activity in the protoplast-derived microcolonies as well as in callus tissues.
Crosses and self's were made among Fragaria × ananassa Duchn. cv. `Douglas' and `Fern' and Fragaria chiloensis (L.) Duchn. Seeds were surface sterilized, germinated and then grown on MS media (no vitamins, sucrose or hormones) with NaCl concentrations of 0 to 0.5% or 0.5% KCl. Polyethylene glycol (PEG), of corresponding water potentials, was used to induce drought stresses. Whole plant dry weights were evaluated after 50 days. Differences in salt tolerance were associated with genotype; progeny involving crosses with F. chiloensis showed greater salt tolerance. Increases in concentration of PEG caused decreased growth. The use of salt containing media may be used to evaluate strawberry seedlings for salt tolerance and, similarly, PEG may be used to evaluate for drought stress in vitro.
Priming tomato (Lycopersicon esculentum Mill) seeds in aerated -0.5 MPa polyethylene glycol (PEG) enhanced the emergence rate and the extent and percentage of embryo radicles protruding partially or completely through the seed endosperm. The radicles' growth, however, was arrested at the seedcoat. The time course of radicle protrusion through the endosperm of seeds in PEG for the first 24 hours paralleled that of seeds germinating in aerated water; however, radicle protrusion continued through the seedcoats of seeds germinating in water. The radicle of the high-vigor PI-341988 tomato line protruded more rapidly through the endosperm than that of the low-vigor ST-24 line.