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Youssef Rouphael, Mariateresa Cardarelli, Giuseppe Colla, and Elvira Rea

inside the chamber in less than 8 s. An equilibration period of 2 to 3 h was required to obtain stable readings of Ψ w . For osmotic potential (Ψ π ), leaf discs taken from the same leaves were wrapped in aluminum foil and rapidly frozen at –35 °C on dry

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D. Joseph Eakes, Robert P. Wright, and John R. Seller

Leaf water relations and gravimetric water loss as influenced by K rate (25, 75, 150, 300, 450 and 600 ppm) and moisture stress conditioning (MSC - exposing plants to 4 sub-lethal dry down cycles) were determined for salvia (Salvia splendens `Bonfire'). K rate and MSC had a synergistic effect on leaf osmotic potentials. Osmotic potentials at both full and zero turgor decreased with increasing K rate and MSC. Differences between MSC and no-MSC plant osmotic potentials increased as K rate increased. Active osmotic adjustment with increasing K rate and MSC resulted in increased cellular turgor potentials. Both high K rates and MSC reduced plant gravimetric water loss on a unit leaf area basis.

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Yingmei Ma and Emily Merewitz

based on turf color, uniformity, and density. Fig. 2. Leaf osmotic potential of creeping bentgrass ‘PsgSLTZ’ and ‘Penncross’ exposed to salt stress treatment in ( A ) Expt. 1, which was started on 21 Dec. 2013, and ( B ) Expt. 2, which was started on 6

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Suejin Park, Youyoun Moon, and Nicole L. Waterland

treatment, additional sodium-containing chemicals (NaCl, NaNO 3 ) and barium-containing chemicals [BaCl 2 and Ba(NO 3 ) 2 ] were used. As an osmotic control, mannitol was applied. Osmotic potential (ψ S ), instead of chemical concentration, was used to

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Douglas D. Archbold

Maintenance of positive cell turgor is an essential factor in cell, and fruit, expansion. Since apple fruit partition carbohydrates between the starch and soluble pools to maintain turgor, variation among cultivars in this osmoregulatory aspect may play an important role in defining cultivar-specific fruit growth rates. Cultivar-specific apple fruit growth rates were determined over a 6 week period following June drop during 2 seasons. Fruit water relations parameters and carbohydrate levels were also measured. Although cultivar differences were evident, generally, fruit absolute growth rate increased, relative growth rate (RGR) declined, water potential and osmotic potential declined, and turgor potential increased as the season progressed. Soluble carbohydrate levels increased over 6 weeks, while starch levels fluctuated. Soluble carbohydrates contributed 50 to 90% of the osmotic potential. RGR was not correlated to either turgor potential or the relative allocation of carbohydrates between the soluble and starch pools. Thus, although positive turgor was maintained, factors other than turgor per se determine fruit growth rate.

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Robert M. Frymire and Janet C. Cole

Uniform rooted cuttings of pyracantha (Pyracantha coccinea M.J. Roem. 'Lalandei') were potted into 3.8 liter containers in a pine bark:sand medium. Plants were treated with a medium drench at 0.5 mg ai per container, or a foliar spray at 150 mg ai per liter, or no uniconazole. Plants also were exposed to one of three irrigation regimes: nonstressed, stressed or acclimated. Uniconazole had little effect on leaf water potential, osmotic potential, transpiration or leaf conductance. The uniconazole drench treatments reduced plant growth and increased N, Ca, and Mn concentrations in the leaves. Foliar applications had less effect on plant growth and elemental content Acclimated and stressed plants had lower water and osmotic potentials, transpiration rates and leaf conductance than nonstressed plants on the final day of the stress cycle. Acclimated plants had higher levels of N and Mn with lower levels of Zn in the leaves than either stressed of nonstressed plants.

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S.I. Shibairo, M.K. Upadhyaya, and P.M.A. Toivonen

The effect of potassium (K) nutrition on the shelf life of carrots was studied using a hydroponics system involving rockwool slabs as support. Carrots were grown for 192 days under greenhouse conditions and supplied with 0, 0.1, 1.0, 10, and 15 mm of K. Increase in K concentration in the nutrient medium decreased postharvest weight loss. Carrot weight and tissue K content increased and water potential, osmotic potential, and relative solute leakage decreased with increasing K concentration in the nutrient feed. Differences in postharvest weight loss were mainly associated to root weight and relative solute leakage. Root weight correlated negatively and relative solute leakage correlated positively to water loss. Water and osmotic potential also correlated to water loss, but not as strongly as root weight and relative solute leakage. These results suggest that K nutrition influences postharvest weight loss by influencing carrot size and membrane integrity. Effects on cell water and osmotic potential are also important in this regard but to a lesser extent.

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Robert Augé and Ann Stodola

Using psychrometric pressure-volume analysis, root water relations following drought were characterized in Rosa hybrida L. plants colonized by the vesicular-arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith. Measurements were also made on uncolonized plants of similar size and adequate phosphorus nutrition. Under well-watered conditions mycorrhizal colonization resulted in lower solute concentrations in root symplasm, and hence lower root turgors. Following drought, however, mycorrhizal roots maintained greater turgor across a range of tissue hydration. This effect was apparently not due to increased osmotic adjustment (full turgor osmotic potentials were similar in mycorrhizal and nonmycorrhizal roots after drought) or to altered elasticity but to an increased partitioning of water into the symplast. Symplast osmolality at full turgor was equivalent in mycorrhizal and nonmycorrhizal roots but because of higher symplastic water percentages mycorrhizal roots had greater absolute numbers of osmotic (symplastic) solutes. Drought-induced osmotic potential changes were observed only in mycorrhizal roots, where a 0.4 megapascal decrease (relative to well-watered controls) brought full turgor osmotic potential of mycorrhizae to the same level as nonmycorrhizal roots under either moisture treatment.

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Hiroshi Yakushiji, Hiroshi Nonami, Toshio Fukuyama, Sukeyuki Ono, Nobuo Takagi, and Yasushi Hashimoto

The effect of water stress induced to enhance sugar accumulation in Satsuma mandarin (Citrus unshiu Marc.) fruit was investigated. Satsuma mandarin trees were subjected to water stress using mulch cultivation from late August to early December. In mulch treatment, soil was covered with double-layered plastic sheets that prevented rainfall from permeating the soil, but allowed water from soil to evaporate. The water status of soil, fine roots, pericarps, and juice vesicles was determined using the isopiestic psychrometer. As the severity of water stress increased, both water potential and osmotic potential of fine roots and pericarps significantly decreased in plants grown under mulch cultivation compared to well-watered trees. Although water potential and osmotic potential decreased, turgor of both roots and pericarps of the water stressed trees did not decrease under water stress conditions. Because turgor was maintained, osmoregulation occurred in Satsuma mandarin trees in response to water stress. The osmotic potential of juice vesicles in water-stressed fruit gradually decreased, and sugars accumulated in vesicle cells. Concentrations of sucrose, fructose, and glucose increased in fruit sap under water stress, and the acidity in the fruit juice increased. Furthermore, the total sugar content per fruit of water stressed trees was significantly higher than in fruit of well-watered trees. These results suggest that sugar accumulation in Satsuma mandarin fruit was not caused by dehydration under water stress but rather that sugars were accumulated by active osmoregulation in response to water stress. When sugar components in osmoregulated fruit were analyzed, it was found that monosaccharides, i.e., glucose and fructose, were largely responsible for active osmoregulation in fruit under water stress conditions.

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Emma L. Locke*, Cecil Stushnoff, Joyce C. Pennycooke, and Michelle Jones

Salinity, drought and temperature frequently limit crop productivity. Transgenic Petunia ×hybrida cv. Mitchell with altered endogenous raffinose family oligosaccharides (RFO) due to over-expression (sense) or under-expression (antisense) of the tomato α-galactosidase gene show that antisense increases in RFO are associated with greater tolerance to freezing stress (Pennycooke et al., 2003). Because vegetative propagules of these antisense lines rooted and established more quickly than their sense counterparts, we hypothesized that antisense lines would also respond to salinity and wilting stress. Salinity treatment plants were exposed to 50-200 mm NaCl graduated 25 mm every 3 days and held at 200 mm for 13 days. Dry-down treatments were watered to pot capacity, then not watered until the onset of wilting. This was repeated in cycles for 26 days. Data were collected on plant growth, root/shoot ratios, and leaf water potential. Fresh and dry weights in four of the six antisense lines exceeded the wild type and sense lines. Osmotic potential for salinity and dry-down plants was 160% to 220% higher than control plants. Pearson correlations revealed that higher osmotic potential was partially associated with higher fresh weight (r = 0.7214, P = 0.02) and root/shoot ratios (r = -0.7414, P = 0.02) in salinity stressed plants. In the dry-down drought stressed plants, osmotic potential was not associated with fresh weight (r = 0.3364, ns) nor root/shoot ratio (r = -0.0431, ns). Salinity stress reduced root mass compared to control and dry down plants. Sense plants grew slowly and were highly variable.