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Yajun Chen, Jingjin Yu, and Bingru Huang

for 6 h at 23 °C. Leaf samples were then blotted dry and immediately weighed for determination of TW. Samples were then dried in an oven at 80 °C for 72 h and weighed again for DW ( Bagatta et al., 2008 ). Leaf osmotic potential (ψ S ) was measured at

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Robert Savé, Josep Peñuelas, Oriol Marfà, and Lydia Serrano

Field-grown strawberry (Fragaria × annanasa Duch. cv. Chandler) plants were subjected to two irrigation regimes from Nov. 1989 to July 1990 to evaluate the physiological and morphological effects of mild water stress. Irrigation was applied when soil matric potential reached -10 and-70 kPa for the wet and dry treatments, respectively. During the spring, these regimes did not promote significant changes in plant water relations, transpiration rates, plant morphology, or canopy architecture. However, during the summer, after several stress cycles, significant differences between treatments were observed. Pressure-volume curves of dry-treatment plants indicated that leaf osmotic potentials, measured at full and zero turgor, decreased 0.2 to 0.4 MPa. This decrease in osmotic potential also was accompanied by a 50% increase in the modulus of elasticity for these water-stressed plants compared to well-watered plants. Dry-treatment plants also showed stress avoidance mechanisms in changes of whole-plant morphology and canopy architecture, from monolayer to polylayer leaf distribution and leaf orientation from south to north. Despite what would appear to be useful drought-resistance strategies, there was significantly lower fruit production by plants grown under the dry treatment.

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Pedro Perdomo, James A. Murphy, and Gerald A. Berkowitz

Understanding the factors influencing the performance of Kentucky bluegrass (Poa pratensis L.) cultivars under summer stress is necessary for developing criteria for identifying resistant germplasm. The objectives of this study were to evaluate two Kentucky bluegrass cultivars for leaf water (ψl) and osmotic potential (ψπ), stomatal resistance (Rs), leaf: air temperature differential (ΔT) and determine the relationship of these parameters to drought and heat tolerance. Stress-resistant (`Midnight') and susceptible (`Nugget') cultivars were evaluated in a field study during 1993 and 1994 under moisture-limiting conditions. Leaf water potential for `Nugget' was higher than for `Midnight' in 1993 and similar in 1994. `Midnight' had lower ψπ than `Nugget' during the evaluation period in 1994. `Midnight' maintained more open stomata (lower Rs) and lower ΔT than `Nugget' at the end of the dry down period when `Nugget' was showing visual signs of stress. `Midnight' and `Nugget' had similar root weight at the 0- to 45-cm depth zone in 1994. Lower basal osmotic potential (i.e., higher solute concentration) may be the physiological mechanism allowing larger stomatal aperture in `Midnight'. Greater transpirational cooling in `Midnight' relative to `Nugget' was correlated with higher turf quality for `Midnight'.

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Nanqing Liu, Yixin Shen, and Bingru Huang

during drought and recovery for colonial bentgrass, creeping bentgrass, and velvet bentgrass J. Amer. Soc. Hort. Sci. 131 484 490 Fu, J. Huang, B. Fry, J. 2010 Osmotic potential, sucrose level, and activity of sucrose metabolic enzymes in tall fescue in

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Agnes A. Flores-Nimedez, Paul H. Li, and Charles C. Shin

GLK-8903, an experimental product whose main ingredient is produced by hydrogenation of a primary alcohol extracted from plants, showed significant potential in protecting bean (Phaseolus vulgaris L.) plants from chilling injury. The GLK-8903 protection mechanism was assessed by examining several physiological and biochemical responses. The decline in leaf water potential and the increase in osmotic potential caused by chilling exposure to 4C (day/night) were minimized by the application of GLK-8903. Chilling causes an increase in electrolyte leakage, an indication of chilling injury of the plasma membrane. Increased electrolyte leakage was reduced significantly in the GLK-8903-treated plants during chilling. This minimized leakage may be due to less damage of the plasma membrane. Plasmolysis and deplasmolysis studies of the epidermal cells suggest that GLK-8903 is able to reduce the plasma membrane perturbation in the chilling environment, as evident by: 1) the lower permeability coefficient to urea at 4C, and 2) the swelling of protoplasts in the cells of untreated tissues after chilling exposure with no swelling of the protoplast being observed in the GLK-8903-treated cells. Malondialdehyde (MDA), a product of lipid peroxidation, increased more in untreated controls than in treated plants exposed to 4C. Plasma membrane ATPase activity decreased less in GLK-8903-treated plants than in untreated controls after 3 days at 4C. The mechanism of GLK-8903-alleviated chilling injury is discussed.

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Stan D. Wullschleger and Derrick M. Oosterhuis

Growth-chamber studies were conducted to examine the ability of seven vegetable crops-`Blue Lake' bean (Phaseolus vulgaris L.), `Detroit Dark Red' beet (Beta vulgaris L.), `Burgundy' okra (Abelmoschus esculentus (Moench), `Little Marvel' pea (Pisum sativum L.), `California Wonder' bell pepper (Capsicum annuum L.), `New Zealand' spinach (Spinacia oleracea L.), and `Beefsteak' tomato (Lycopersicon esculentum Mill.)–to adjust osmotically in response to water-deficit stress. Water stress was imposed by withholding water for 3 days, and the adjustment of leaf and root osmotic potentials upon relief of the stress and rehydration were monitored with thermocouple psychrometers. Despite similar reductions in leaf water potential and stomata1 conductance among the species studied, crop-specific differences were observed in leaf and root osmotic adjustment. Leaf osmotic adjustment was observed for bean, pepper, and tomato following water-deficit stress. Root osmotic adjustment was significant in bean, okra, pea, and tomato. Furthermore, differences in leaf and root osmotic adjustment were also observed among five tomato cultivars. Leaf osmotic adjustment was not associated with the maintenance of leaf growth following water-deficit stress, since leaf expansion of water-stressed bean and pepper, two species capable of osmotic adjustment, was similar to that of spinach, which exhibited no leaf osmotic adjustment.

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Thomas E. Marler and Yasmina Zozor

Leaf gas exchange, chlorophyll fluorescence, water relations, and mineral nutrient relations responses of Annona squamosa seedlings to mild salinity were studied in sand culture in five experiments during 1990, 1991, and 1993. Trees were irrigated with a complete nutrient solution (control) or with this solution amended to 3 or 6 dS·m-1 with sea salt. Inhibition of net CO2 assimilation, stomatal conductance of CO2, and transpiration was apparent within 2 weeks of initiating salinity treatments, and gas exchange continued to decline until day 30 to 35. The diurnal pattern of leaf gas exchange was not altered by increased salinity. Salinity reduced CO2, light energy, and water-use efficiencies. Salinity sometimes reduced the ratio of variable to maximum fluorescence below that of the control, and this response was highly dependent on the ambient light conditions that preceded the measurements. Dark respiration was unaffected by salinity stress. Root zone salinity of 3 dS·m-1 administered for 52 days did not influence foliar sodium concentration or the ratio of sodium to potassium, but increased chloride concentration and decreased nitrogen concentration. The sodium response indicated that some form of exclusion or compartmentation occurred. Salinity reduced osmotic potential of root tissue but did not influence foliar osmotic or predawn xylem potential. These results indicate that A. squamosa is sensitive to salinity stress, and that the responses to salinity are consistent with other salt-sensitive woody perennial species.

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Smita Barkataky, Robert C. Ebel, Kelly T. Morgan, and Keri Dansereau

water potential measured using a pressure chamber (Model 3005 plant water status console; Soil Moisture Equipment Corporation, Santa Barbara, CA). Osmotic potential. Ψ π was measured in the first experiment. Immediately after measuring Ψ stem , a 7-mm

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Thomas G. Ranney, Nina L. Bassuk, and Thomas H. Whitlow

Abbreviations: Ψ π , osmotic potential; Ψ π,sat , osmotic potential at full turgor. 1 Present address: North Carolina State Univ., Dept. of Horticultural Science, Mountain Horticultural Crops Research and Extension Center, 2016 Fanning Bridge Road

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Robert M. Augé, Ann J.W. Stodola, and Brian D. Pennell

water content at the turgor loss point; RWC 0 , relative water content; RWC, relative water content at the turgor 1 0ss point; Ψ, water potential; Ψ π , osmotic potential; Ψ π 100 , osmotic potential at full turgor; Ψ π o , osmotic potential at the