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Gayle Volk, Virgil Esensee, and Harrison Hughes

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.

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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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Jennifer A. Ehrenberger* and Adelheid R. Kuehnle

A hybridization strategy for certain coloration could be developed based on accurate histological information of parental material together with the knowledge of heritability of color and color intensity. A sample of 12 Anthurium species and hybrids were histologically examined for pigmentation in spathes using a new method employing vacuum infiltration of spathe tissue with polyethylene glycol (PEG) prior to cross-sectioning. PEG infiltration displaces intercellular air spaces between cells. This method greatly improved the clarity of the cross sections and consequently improved observations of spatial localization of anthocyanins and chloroplasts. This infiltration method accurately identified the spatial localization of pigments for future breeding reference, notably among Anthurium species.

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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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Zhongchun Wang and Gary W. Stutte

Previous results showed that active sorbitol accumulation occurs under water stress. We tested the hypotheses that sorbitol accumulation is due to reduced sorbitol export from leaves or from increased synthesis of glucose to sorbitol. To test the hypotheses, 230 μl 14C-sucrose was introduced through the stems to detached `Jonathan' apple shoots which had either water stress or no stress. Following uptake of 14C-sucrose, 0% or 10% PEG was applied to shoots for 24 hours. The results showed that 73% of 14C-sucrose in non-stressed leaves was broken down within 1 hour and 44% was recovered in sorbitol. PEG initially stimulated the breakdown of 14C-sucrose to glucose and fructose, but further conversion to sorbitol was reduced. However, the percentage of 14C-sorbitol in mature leaves increased gradually in 10% PEG until it exceeded that of control at 24 hours. In contrast to mature leaves, young leaves and stems showed significantly less sorbitol under 10% PEG 24 hours after treatment. These results supported the hypothesis that sorbitol accumulation under water stress was due to the reduced sorbitol transport.

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Stephanie E. Burnett, Svoboda V. Pennisi, Paul A. Thomas, and Marc W. van Iersel

Polyethylene glycol 8000 (PEG-8000) was applied to a soilless growing medium at the concentrations of 0, 15, 20, 30, 42, or 50 g·L-1 to impose controlled drought. Salvia (Salvia splendens F. Sellow. ex Roem & Shult.) seeds were planted in the growing medium to determine if controlled drought affects morphology and anatomy of salvia. Polyethylene glycol decreased emergence percentage and delayed emergence up to 5 days. Stem elongation of salvia treated with the five lowest concentrations was reduced up to 35% (21 days after seeding), and salvia were a maximum of 53% shorter and the canopy was 20% more narrow compared to nontreated seedlings 70 days after seeding. These morphological changes were attributed to PEG-8000 mediated reduction in leaf water potential (Ψw). The growing medium Ψw ranged from -0.29 to -0.85 MPa in PEG-8000 treated plants, and plant height was positively correlated with Ψw 21 days after seeding. Stem diameter of PEG-treated seedlings was reduced up to 0.4 mm mainly due to reductions in vascular cross-sectional area. Xylem cross-sectional area decreased more than stem and phloem cross-sectional area. Polyethylene glycol 8000 reduced vessel element number, but not diameter.

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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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Leigh E. Towill

Papaya shoot tips, obtained either from seedlings or from in vitro plants, survived liquid nitrogen (-196°C) exposure using a vitrification procedure. Vitrification is a technically simple method but requires large concentrations of cryoprotectants. These were added in two steps, first slow addition of dimethylsulfoxide (DMSO) and PEG-8000, and subsequent fast addition of ethylene glycol (PG). The final concentration before cooling was 40% EG, 7.8% DMSO, and 10% PEG-8000. Both rapid cooling and rapid warming rates were required. Differential scanning calorimetry (DSC) was used to determine that the external solution vitrified upon cooling. It could not be demonstrated by DSC that cells within the shoot-tip vitrified, but since both DMSO and EG rapidly permeate plant cells, vitrification within the cells seems a likely explanation for retention of viability.

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M. Khademi, D. S. Koranski, and P. T. Karlovich

NaCl, KNO3 (0.3, 0.4, 0.5M), KH2P O4 (0.4, 0.5, 0.6M), and PEG 8000 (320 to 370 g/L with the increment of 10g/L) were used for priming Petunia `Ultra White' seeds for three to six days. Seeds were germinated in a growth chamber at 25C. Germination was recorded for seven days and the number of acceptable seedlings (seedlings with open cotyledon and normal root) was counted on the day seven. KH2P O4 at 0.6M was the best salt treatment. Rate of germination was improved by salt priming but the number of acceptable seedlings was lower than the control. Addition of GA (5 ppm) to the salt treatment was not effective. More abnormal seedlings were observed when seeds were primed in aerated salt solutions than when primed in petri dishes. Aerated PEG at 325 g/L for three days and 365 g/L for six days gave the best results. Priming in PEG improved percent of germination, rate of germination, and number of acceptable seedling as compared to control. Primed seeds lost some of the advantages of priming during 24hr air drying (22C), however quality was maintained when dried at 10C. Drying primed seed in 80% R.H. was not effective.

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M. Khademi, D. S. Koranski, and P. T. Karlovich

NaCl, KNO3 (0.3, 0.4, 0.5M), KH2P O4 (0.4, 0.5, 0.6M), and PEG 8000 (320 to 370 g/L with the increment of 10g/L) were used for priming Petunia `Ultra White' seeds for three to six days. Seeds were germinated in a growth chamber at 25C. Germination was recorded for seven days and the number of acceptable seedlings (seedlings with open cotyledon and normal root) was counted on the day seven. KH2P O4 at 0.6M was the best salt treatment. Rate of germination was improved by salt priming but the number of acceptable seedlings was lower than the control. Addition of GA (5 ppm) to the salt treatment was not effective. More abnormal seedlings were observed when seeds were primed in aerated salt solutions than when primed in petri dishes. Aerated PEG at 325 g/L for three days and 365 g/L for six days gave the best results. Priming in PEG improved percent of germination, rate of germination, and number of acceptable seedling as compared to control. Primed seeds lost some of the advantages of priming during 24hr air drying (22C), however quality was maintained when dried at 10C. Drying primed seed in 80% R.H. was not effective.