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Jingjing Yin, Nina L. Bassuk, Madeline W. Olberg, and Taryn L. Bauerle

is referred to as “transplant shock,” in which a plant shows less shoot growth, smaller “scorched” new leaves, and a general lack of vigor ( Watson and Himelick, 1983 ). Root hydraulic conductance describes the ability of roots to take up water from a

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L.S. Chang, A.F. Iezzoni, G.C. Adams, and F.W. Ewers

Abbreviations: K h , hydraulic conductance per pressure gradient. 1 Dept. of Horticulture. Current address: National Taiwan Univ., Taipei, Taiwan, R.O.C. 2 Dept. of Horticulture. 3 Dept. of Botany and Plant Pathology. Acknowledgement is made to the

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Lesley A. Judd, Brian E. Jackson, William C. Fonteno, and Jean-Christophe Domec

and hydraulic conductance (reciprocal of hydraulic resistance) ( Passioura and Munns, 1984 ; Ramos and Kaufmann, 1979 ; Rieger and Litvin, 1999 ). Hydraulic conductance ( K r ) is a measure of the efficiency of bulk flow through plant shoots or roots

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Manuel G. Astacio and Marc W. van Iersel

to flooding, which decreases both leaf and root hydraulic conductance with root water flux decreasing to 50% of the pre-stress level within 8 h ( Bradford and Hsiao, 1982 ). Bradford and Hsiao (1982) concluded that stomatal closure, along with

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Hiroshi Wada, Mari Iwaya-Inoue, Mitsuru Akita, and Hiroshi Nonami

Two cultivars of tulip (Tulipa gesneriana L.) were used to check the effect of trehalose-feeding on longevity of vase life. `Oxford' plants were grown from bulbs, and trehalose-fed cut flowers were compared with the intact plants grown in pots. `Pink Diamond' flowers were obtained commercially as cut flowers from the market, and trehalose-feeding was examined by using only flower parts. In both cultivars of plants, it was confirmed that trehalose-feeding enhanced longevity of the vase life significantly at room temperature. Additionally, mechanisms of prolonging the vase life with trehalose-fed flowers were studied by comparing the water status in the zone of elongation of tulip tepals when their growth rates were modified with different treatments. In the elongating region of tulip tepals, cell elongation rates were linearly correlated to sizes of the growth-induced water potential regardless of treatments. It was found that trehalose-feeding reduced the hydraulic conductance, resulting in a decrease in cell elongation rates. Also, trehalose helped to maintain turgor of tepal cells for longer periods. Furthermore, trehalose enhanced pigmentation in tepals, and thus, trehalose is believed to have had a role in altering the metabolism in elongating cells and in reducing hydraulic conductivity in membranes.

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Albert H. Markhart III and Barbara Smit

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Wouter G. van Doom and René R.J. Perik

Stems of cut rose flowers (Rosa hybrids L., cvs. Sonia, Ilona, Polka, and Frisco) were held in a sodium hypochlorite solution and then placed in distilled water or in a buffer at pH 6.0. After 2 days, many bacteria were found in the basal end of the stems, even when the number of bacteria in the water was below the detection limit. The hydraulic conductance of 5-cm stem segments was reduced whenever the number of bacteria exceeded =106 cfu/g fresh weight. Adding HQC or a buffer at pH 3.0 limited the number of bacteria in stems. Hydraulic conductance of the stems held in these solutions for 2 days was as in stems of freshly harvested flowers. Thus, HQC and low pH prevent vascular blockage by reducing the number of bacteria in the stems. No evidence was found for the hypothesis that HQC and low pH inhibit a stem-induced vascular blockage.

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Patricia R. Knight, J. Roger Harris, and Jody K. Fanelli

Root severance during field harvesting alters the water status of a tree, resulting in water stress and reduced post-transplant growth. Two experiments, using Acer rubrum L. (red maple), determined the influence of root severance at harvest on sap flow and xylem embolism. Trees 1.5–1.8 m tall (4 years old) were utilized in the first experiment, and trees 1.2–1.5 m tall (2 years old) were utilized in the second. Sap flow sensors were installed on the 4-year-old trees prior to root severance and remained on the trees until 1 week after harvest. Within 1 day after root severance sap flow was reduced and remained lower than nontransplanted (control) trees for the remainder of the experiment. Leaf stomatal conductance (Cs) of transplanted trees 1 week after root severance was lower than that of control trees, but leaf water potentials (ψ) were similar. In the second experiment, sap flow was reduced relative to control trees within 2 h after root severance. Although Cs was reduced 4 hours after root severance, ψ was not. Embolism increased within 24 hours of root severance. These results indicate that root severance quickly induces increased levels of embolism, which is associated with reduced sap flow.

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Gretchen B. North and Evan A. Baker

region in dry soil. In addition, hydraulic conductance (a root's capacity to absorb and transport water) is higher for segments of older roots from the wet soil compartment than it is for younger segments from dry soil ( North and Nobel, 2000 ). An

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Aidan D. Farrell, Sarah Evelyn, Adrian M. Lennon, and Pathmanathan Umaharan

in hydraulic conductance and RWC of the stem apparently resulting from cavitation. Our conclusion does not support the previous suggestion that water stress in the anthurium spathe is the result of occlusion at the base of the peduncle ( Elibox and