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Qi Zhang, Liqi Yang and Kevin Rue

524 Mexal, J. Fisher, J.T. Osteryoung, J. Reid, C.P. 1975 Oxygen availability in polyethylene glycol solutions and its implications in plant-water relations Plant Physiol. 55 20 24 Michel, B.E. Kaufmann, M.R. 1973 The osmotic potential of polyethylene

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A. Liptay and N. Zariffa

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.

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Farida Safadi and Harrison Hughes

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.

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Aaron J. Brown

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.

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Masooma Ali-Ahmad and Harrison Hughes

Scanning electron microscopic (SEM) studies and gravimetric analysis of in vitro cultured leaf surfaces showed reduced epicuticular wax (EW) structurally and quantitatively as compared to greenhouse plants. However, leaves of in vitro plantlets subjected to polyethylene glycol-treatment (PEG) showed an increase in quantitative and structural EW which was similar to that of greenhouse plants. Furthermore, leaves initiated during in vitro culture and which persisted, when transferred to the greenhouse, showed an increase in structural wax as well as in amount, 30 days after transplanting in the greenhouse. Similarly, leaves newly-formed in the greenhouse from in vitro cultured plants developed more dense crystalline structure and greater levels of wax than those leaves observed immediately after removal from culture. A correlation between density of structural EW and amount of EW were observed in in vitro cultured, PEG-treated in vitro cultured and greenhouse grown leaves.

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Eucario Mancilla-Álvarez, Marco A. Ramírez-Mosqueda, Samantha Arano-Avalos, Rosalía Núñez-Pastrana and Jericó J. Bello-Bello

retardants such as ancymidol ( El-Dawayati et al, 2012 ; Sarkar et al., 2001 ), and osmoregulators as polyethylene glycol (PEG-800) ( Seesangboon et al., 2018 ). In plant physiology, ancymidol produces a number of effects, including the inhibition of

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Masooma Ali-Abmad and Harrison Hughes

Scanning electron microscopy was used to study stomatal function of grape (Vitis sp. `Valiant') plantlets grown in vitro, polyethylene glycoltreated (PEG) in vitro and greenhouse. Fully open stomata were observed in in vitro grown plants with large aperture (13.5μm) as compared to narrow stomatal opening and small aperture in PEG-treated (4.9pm) and greenhouse grown plants (3.2μm). Furthermore, stomates of persistent leaves initiated during in vitro culture remained fully open with large apertures (12.8μm) two weeks after transplanting in the greenhouse. In contrast, newly-formed leaves produced in the greenhouse from in vitro cultured plants showed narrow stomatal opening with small apertures (3.3μm). In vitro produced leaves exhibited rapid wilting followed by irreversible tissue damage and severe desiccation within three hours of transplantation into the greenhouse. However, PEG-treated plantlets showed a reduced stomatal opening with associated minimal stress when directly transferred into the greenhouse. Thus use of an osmotic agent, PEG, induced more normal stomata1 function as well as improved survival after transfer to the greenhouse.

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Kourosh Vahdati, Naser Lotfi, Bahman Kholdebarin, Darab Hassani, Reza Amiri, Mohammad Reza Mozaffari and Charles Leslie

to simulate drought stress in vitro ( Pandey and Agarwal, 1998 ). Polyethylene glycol molecules (PEG 6000) are osmotically active, inert, nonionic, and virtually impermeable to plant cells and are frequently used to induce water stress and maintain

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Trygve S. Aamlid and Peter J. Landschoot

equivalent osmotic potentials created by SMS extract or polyethylene glycol on germination of perennial ryegrass and Kentucky bluegrass. In Dec. 2005, a new saturated paste extract was made based on the same SMS used in expt. 1. This extract showed an ECe

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Glen A. Murray, Jerry B. Swensen and Gary Beaver

The effect of osmotic priming on onion (Allium cepa L.) seedling emergence was evaluated in the field and in a controlled environment at 15C. Seeds of onion cultivars Bronze Wonder, Challenger, Big Mac, and White Keeper were primed in a solution of 300 g polyethylene glycol 8000/liter for 7 days at 10C 1 to 2 weeks before being planted in Spring 1986 and Summer 1987. Time to 50% of maximum emergence (T) for seedlings from primed seeds averaged 10% to 12% less than for unprimed seeds in both seasons and in laboratory experiments. Maximum emergence was improved 7% by priming in one spring field experiment but not in the summer field experiments or in the laboratory. Differences in T among cultivars in the 1986 experiments were small and significant only in one laboratory experiment. In 1987, cultivar differences in T were significant but not consistent in all experiments. Cultivar T means from laboratory experiments were significantly (P = 0.05) correlated with those for field emergence in three of four experiments, but coefficients were low (r = 0.37 to r = 0.45). Values for maximum emergence in the laboratory were not correlated with maximum emergence in the field. Laboratory emergence tests at 15C were a poor predictor of field emergence. Seed priming may benefit establishment of spring-seeded onions emerging at soil temperatures ≤ 15C more than summer-seeded onions emerging in soils >24C.