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James Q. Garner Jr. and Thammasak Thongket

Proline content, leaf water potential (LWP), and leaf diffusive resistance (LDR) were determined for eight sweetpotato genotypes underwater stress conditions. Changes in fatty acid compositions of leaf polar lipids were determined in two sweetpotato genotypes during declining soil moisture. Proline did not accumulate and LWP did not decrease until soil moisture dropped below 10%, but LDR increased as soil moisture decreased. Genotypic differences in proline accumulation and LWP were found. Changes in fatty acid compositions occurred more in glycolipids than in phospholipids. Fatty acid changes were more pronouned in genotype MS20-2 than in “Vardaman”

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Yoel Bar, Akiva Apelbaum, Uzi Kafkafi, and Raphael Goren

A study was conducted to elucidate the effects of chloride in the irrigation water on growth and development of two citrus rootstocks. `Cleopatra' mandarin (Citrus reshni Hort. ex Tan) is salt tolerant and `Troyer' citrange (Poncirus Citrus sinensis) is salt sensitive. Increasing chloride from 2 to 48 mm in the irrigation water resulted in increased leaf chloride levels, more severe damage of the leaves, and reduced branch growth. High chloride in the irrigation water also caused increased putrescine (PUT) and decreased spermine (SPM) contents of the leaves. These effects were slight in `Cleopatra' but highly apparent in `Troyer'. The symptoms caused by high chloride were associated with high PUT and low SPM levels in the leaves. PUT may be involved in the development of chloride toxic symptoms, and SPM may protect or have no effect on chloride plant injury. The leaf polyamine profiles of `Troyer' and `Cleopatra' under nonstress chloride conditions were different. In `Troyer' leaves, PUT level was 9-fold higher than in `Cleopatra'; in `Cleopatra' leaves, SPM level was 25-fold higher than in `Troyer'. Nitrate supplement to saline water reduced chloride accumulation in the leaves and reduced the increase in PUT. The possible connection between ethylene production and PUT and SPM levels in the leaves of stressed plants is discussed.

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Chuhe Chen, J. Scott Cameron, and Ann Marie VanDerZanden

170 ORAL SESSION 46 (Abstr. 325-330) Berries: Stress

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S.M. Lutfor Rahman, Eiji Nawata, and Tetsuo Sakuratani

Effects of water stress at different plant ages on SOD activities were studied in two tomato cultivars. Water stress treatment decreased the leaf water potential in all stages, but reduction of leaf water potential was more rapid and pronounced in KF than TM at all DSLs (days of seedlings). After withdrawal of water stress treatment, stressed plants of TM increased leaf water potential to the values of control level in all DSLs, but in KF, leaf water potential of stressed plants were much lower than that of control plants. Effects of water stress on relative water content (RWC) of leaves at 20 DSL showed a similar tendency to that on leaf water potential. The SOD activities in both cultivars showed significant increase by water stress treatment at all DSLs, but the increase of SOD by water stress was larger in TM than in KF. This tendency was observed at all DSLs. The results may indicate that SOD activities play an important role in drought tolerance of tomato at various plant ages and suggest a possible use of SOD activities as a criterion for tomato drought tolerance.

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Mengmeng Gu, James Robbins, Curt Rom, and Hyun-Sug Choi

Poster Session 28—Stress Physiology 29 July 2006, 1:15–2:00 p.m.

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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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D.J. Garrot Jr., M.W. Kilby, D.D. Fangmeier, and S.H. Husman

192 ORAL SESSION (Abstr. 754-761) FRUIT CROPS: STRESS PHYSIOLOGY

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Molla Md. Nuruddin, Chandra A. Madramootoo, and Georges T. Dodds

Tomatoes (Lycopersicon esculentum Mill. cv. Sunstart) were grown in a greenhouse during Summer 1999 and again in Winter 2000. Two available soil water (ASW) deficit thresholds, 65% and 80%, at which plants were irrigated to field capacity were factorially combined with five irrigation timing patterns: 1) no water stress; 2) stress throughout the entire growing season; 3) stress during first cluster flowering and fruit set 4) stress during first cluster fruit growth; and 5) stress during first cluster fruit ripening. Crop yields, water use efficiency, as well as maximum and minimum equatorial fruit diameters and fruit height were measured. Quality parameters of soluble solids, pH, and fruit color were also measured. Water stress throughout the growing season significantly reduced yield and fruit size, but plants stressed only during flowering showed fewer but bigger fruit than completely non-stressed plants. Consequently, on a weight basis the stressed at flowering and nonstressed plants had similar yields. Nonstressed and flowering-stressed fruit showed lower soluble solids and a lighter color of red ripe fruit than the other stress treatments. No significant differences in yield or quality were found between the two stress levels (65% vs. 80% ASW depletion before irrigation). Water stress only during flowering resulted in better yields and quality than stress at other specific developmental stages or at all times, but equal or poorer yields and water use efficiency than nonstressed plants.

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Terence L. Robinson and Bruce H. Barritt

Abbreviations: ABA, abscisic acid; c, t-ABA, cis, trans-abscisic acid; LPI, leaf plastochron index; PI, plastochron index age; ψ P , leaf turgor pressure; ψ S , leaf osmotic potential; ψ W , leaf water potential; t , t-ABA, trans, trans

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

To understand the relationship between preharvest water stress and postharvest weight loss, carrot cultivars Eagle and Paramount were grown in muck soil in 6-L pots (eight carrots per pot) in a greenhouse at the Univ. of British Columbia. The plants were watered to field capacity every second day for 4 months before receiving 100, 75, 50, and 25% field capacity water stress treatments, henceforth referred to as low, medium, high, and severe water stress, respectively. Postharvest weight loss of carrots was monitored at 13°C and 32% relative humidity. Carrot weight loss increased with duration of storage in all treatments. It was low in the low-water-stressed and high in severely water-stressed carrots for both cultivars. Root crown diameter, weight, water, and osmotic potential decreased, and specific surface area and relative solute leakage increased with increasing preharvest water stress. Water potential followed by relative solute leakage were the variables that affected weight loss the most. The results show that carrots adjust to water stress by lowering water and osmotic potential. Preharvest water stress lowers membrane integrity of carrot roots making them lose more moisture during storage.