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Imed Dami and Harrison Hughes

Grape cv. Valiant was micropropagated in an MS medium with and without 2% (W/V) of polyethylene glycol (PEG, MW 8000). Leaf anatomy of control (in vitro, no PEG), treated (in vitro, PEG), field grown and greenhouse grown plants were compared under light microscopy. Cell size, palisade layer formation, relative intercellular air space and apparent chloroplast number varied between the leaves of control and PEG treated (high osmoticum) plantlets. These leaf characteristics in the high osmoticum medium appeared more similar to the leaves of the greenhouse and field grown plants. Leaves from control plantlets contained cells of larger size, lacked normal palisade layer formation, greater intercellular pore spaces and fewer chloroplasts. Leaves of PEG treated plantlets had smaller cells, a more defined palisade layer, reduced intercellular pore spaces and greater number of chloroplasts. Leaves of greenhouse and field grown plants had small cells, a well-defined palisade layer, least intercellular pore space and greatest number of chloroplasts. These results demonstrate that a high osmoticum medium may be used to induce more normal leaf development.

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Isabelle Lemay, Jean Caron, Martine Dorais, and Steeve Pepin

., 2005 ). Alternatively, measurement of substrate matric potential is a method that has long been available to growers ( Frenz and Lechl, 1981 ; Norrie et al., 1995 ), but the optimal soil water potential used as the basis for initiating irrigation

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Elvia Hernández-Gómez, Luis A. Valdez-Aguilar, Ana M. Castillo-González, María T. Colinas-León, Donita L. Cartmill, Andrew D. Cartmill, and R. Hugo Lira-Saldívar

harvesting fruits that met market quality when ripe (≈50% of fruit exterior had turned red) throughout the study period. Photosynthetic parameters, transpiration rate, and leaf water potential. Photosynthetic rate, g S , transpiration rate (LI-6200; LI

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Moritz Knoche, Eckhard Grimm, and Henrik Jürgen Schlegel

calculated water potential ( ) for mature ‘Sam’ and ‘Samba’ at varying depth. Data for were redrawn from B . The was calculated as the sum of of expressed juice plus the for ‘Sam’ and ‘Samba’, respectively. Note that as a result of the very low

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R.C. Beeson Jr.

Photinia plants produced in 11.4-liter polyethylene containers using a pine bark-based medium were transplanted into a well-drained sand and irrigated on alternate days. Polyethylene barriers were placed under half the root balls at transplanting to limit gravitational water loss. Plant water potential was measured diurnally between irrigations, and root growth was determined at 4-month intervals. Plants with barriers averaged higher cumulative daily water stress than control plants over the year, although predawn and minimum water potentials were similar. Growth index and trunk diameter were similar for the plants over barriers and controls, but the former were taller after 1 year. Plants with barriers had twice the horizontal root growth into the landscape site as control plants, resulting in twice the root mass in the landscape after 1 year.

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Takashi Ikeda, Yukihiro Fujime, Satoshi Terabayashi, and Shuichi Date

Garlic (Allium sativum L.) calli in vitro were evaluated over a range of salt concentrations and by adding mannitol to culture medium with reduced salt to provide equivalent osmoticum. The water potential of the medium ranged from -0.27 to -0.73 MPa under the various salt and osmotic stress conditions. The percent increase in calli was highest in standard Murashige & Skoog (MS) medium and was reduced when MS salts were reduced but the water potential of medium was adjusted to that of standard MS medium by addition of mannitol. The water potential of callus tissue was similar to that of tissue culture media over a 20-fold range (10% to 200%) of MS concentrations. Turgor of callus tissue was not influenced by any stress conditions. These results indicate that the optimum concentration of salt and water status of medium for formation of garlic calli was provided by standard MS medium.

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Kenji Kobashi, Hiroshi Gemma, and Shuichi Iwahori

A water stress treatment was imposed on peach trees [Prunus persica (L.) Batsch `Kansuke Hakuto' (Peach Group)] to elucidate the relationship among sugar accumulation, sugar metabolism, and abscisic acid (ABA) in fruit under water stress. Treatment was carried out on peach trees grown in containers from 8 July 1996 [80 days after full bloom (DAFB)] for 16 days, to achieve a predawn water potential of -0.8 to -1.1 MPa compared to that of -0.4 to -0.6 MPa in control trees. Levels of sorbitol, sucrose, and total sugars, as well as the activity of sorbitol oxidase increased in fruit of water stressed trees under moderate water stress (-0.8 MPa), whereas under severe water stress (-1.1 MPa), no difference between the waterstressed trees and the controls was observed. Water stress also induced an increase in ABA in the fruit. These initial results indicated that water-stress-induced ABA accelerated sugar accumulation in peaches by activating sorbitol metabolism.

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Wouter G. van Doorn and Yke de Witte

Including bacteria in the vase water of cut Gerbera jamesonii Bolus flowers resulted in an increase in scape curvature depending on the concentration of bacteria in the water, cultivar, and season. In the summer, a strain of Pseudomonas aeruginosa or a mixed population of bacterial species, all isolated from the vase water of cut gerbera flowers, resulted in curvature of >90° in `Liesbeth' at 108 cfu/ml and in `Mickey' at 1010 cfu/ml. In winter, the lowest bacterial concentrations that resulted in such bending were 106 and 108 cfu/ml, respectively. `Mickey' showed bending at a lower water potential than `Liesbeth'. Comparison between these results and the bacterial counts in vase water and water at retail shops indicates that frequently observed scape bending is at least partly due to bacteria.

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Tomasz Anisko and Orville M. Lindstrom

The effect of water stress imposed at three dates in late summer and early fall on cold hardiness was examined in Rhododendron L. `Coral Bell', `Hinodegiri', and `Red Ruffle'. The persistence of the water stress-induced cold hardiness was also examined following plant recovery from the stress. Container-grown plants were exposed to three weeks of reduced water supply starting 8 Aug., 29 Aug., or 19 Sept., while control plants were well watered. Cold hardiness of leaves, lower, middle, and upper stems was evaluated with laboratory freeze tests. Reduced water supply independent of time initiated increased cold hardiness by 1 to 4C in the majority of the tested plant parts in the three cultivars. Cold hardiness of all plant parts tested strongly depended on the current water status of the plants as indicated by the stem water potential. In most cases, 3 weeks after rewatering, the cold hardiness of previously water stressed plants did not differ from that of nonstressed plants.