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Kanogwan Kerdnaimongkol, Anju Bhatia, Robert J. Joly, and William R. Woodson

Diurnal variation in the chilling sensitivity of tomato seedlings was examined. Sensitivity to chilling in tomato seedlings is a response to light and not under the control of a circadian rhythm. Chilling sensitivity is highest in seedlings chilled at the end of the dark period, and these seedlings become more resistant to chilling injury upon exposure to the light. Diurnal variation in chilling sensitivity was associated with changes in catalase and superoxide dismutase activities. The results show an increase in catalase and superoxide dismutase activities at the end of the light period. The recovery of the net photosynthesis rate following chilling was faster in seedlings chilled at the end of the light period. It is suggested that an increase in catalase and superoxide dismutase activities at the end of light period before the chilling plays a role in the resistance to chilling stress in tomato seedlings. Forty-eight hours of 14°C acclimation or hydrogen peroxide pretreatment conferred chilling tolerance to tomato seedlings and were correlated with elevated catalase activity. Acclimated seedlings still exhibited diurnal variation in chilling sensitivity while hydrogen peroxide treated seedlings showed little evidence of a diurnal variation in chilling sensitivity. Transgenic tomato plants expressing an antisense catalase gene were generated. A several-fold decrease in total catalase has been detected in the leaf extracts of transformants. Preliminary analysis of these plants indicated that modification of reactive oxygen species scavenging in plant system can lead to change in oxidative stress tolerance.

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Georges T. Dodds, J. Wyatt Brown, and Pamela M. Ludford

Chilling of mature-green (MG) tomato fruit (Lycopersicon esculentum Mill. and related species) was investigated to determine the effect of chilling stress on surface color during low-temperature storage. Color measurements were made with a tristimulus calorimeter (L, a, b values), and data were analyzed by multivariate analysis of variance and canonical variates analysis. Changes in surface color of MG fruit during chilling were not correlated overall with relative chilling sensitivity of cultivars/lines; however, within standard and cherry types, chilling-tolerant fruit changed surface color more during chilling than chilling-sensitive fruit when fruit were picked early in the season. Early harvests were less chilling-sensitive than late harvests. The number of hours below 15.6C in the 200 hours before harvest was positively correlated with postharvest chilling sensitivity. A high vs. ambient relative humidity during storage did not affect chilling-induced percent change in color. Tobacco mosaic virus resistance led to less and Verticillium albo-strum Reinke & Berthier resistance led to more chilling-induced color change. There was no effect from resistances to Fusarium oxysporum Schlechtend f. sp. lycopersici (Sacc.) W.C. Snyder & H.N. Hans, alternaria stem canker (Alternaria solani Sorauer), anthracnose [Colletotrichun coccodes (Wallr.) S.J. Hughes], root-knot nematode (Meloidogyne hapla Chitwood), Phytophthora infestans (Mont.) deBary, or Stemphylium botryosum f. sp. lycopersici Rotem, Cohen, & Wahl. Our results show harvest date had an effect on chilling-induced changes in surface-color in MG fruit.

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Mary E. Mangrich and Mikal E. Saltveit

Chilling 10-mm cucumber (Cucumis sativus L. `Poinsett 76') radicles at 2.5 °C reduced their subsequent growth during 3 days at 25 °C. The reduction in radicle growth was linear for 1 to 3 days of chilling but then increased substantially until subsequent radicle growth was all but eliminated by 6 days of chilling. Heat shocks of 40 °C applied for 4 to 12 min increased chilling tolerance such that 4 days of chilling caused only a 36% decrease in radicle growth compared to 66% for seedlings not heat shocked, which brought the response in line with the responses of the non-heat-shocked seeds chilled for 1 to 3 days. Eight-minute heat shocks applied before 5 days of chilling resulted in a 45% inhibition of subsequent growth, compared to 82% for chilled non-heat-shocked controls. Heat shocks applied before 3 days of chilling did not result in a significant increase in subsequent growth compared to the non-heat-shocked controls chilled for 3 days. Heat shocks were only able to protect that part of radicle growth that was in excess of the linear decrease in radicle growth. There appears to be two effects of chilling on radicle growth. The first is linear and cannot be affected by heat shocks. The second is much more severe and can be prevented by heat shocks. Seeds were selected for three categories of vigor according to the rate at which their radicles grew to 10 mm. Seeds classified with different vigors neither responded significantly differently to 3 days exposure to 2.5 °C nor did they respond differently to chilling stress following application of heat shocks.

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Yong In Kuk and Ji San Shin

were correlated with a higher percentage of the younger seedlings surviving chilling stress. Paraquat is a quick-acting contact herbicide that immediately kills cells/tissues that get in contact with the herbicide. In a young leaf, however, damaged

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Peiyan Li, Xiaolin Zheng, Md. Golam Ferdous Chowdhury, Kim Cordasco, and Jeffrey K. Brecht

quarantine hot water treatment (QHWT) under chilling stress was further investigated in this study. Materials and Methods Fruit and treatment Expt. 1. Mature green mango fruit ( Mangifera indica L.) cv. Tommy Atkins were harvested from an orchard at the

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Xinhua Zhang, Fujun Li, Nana Ji, Shujun Shao, Dongyang Wang, Ling Li, and Fansheng Cheng

involvement of polyamines and proline in chilling stress responses has been extensively studied. An increase in polyamines or proline levels is correlated with improved cold tolerance in chilling-sensitive plants ( Cao et al., 2012 ; Mirdehghan et al., 2007

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Misael O. Vega-García, Greici López-Espinoza, Jeanett Chávez Ontiveros, José J. Caro-Corrales, Francisco Delgado Vargas, and José A. López-Valenzuela

immediate response to chilling stress in this cultivar. The H 2 O 2 that is not detoxified by enzymes such as APX and CAT could also be decomposed by peroxiredoxins (Prx), thiol-dependent peroxidases that can reduce a wide range of active oxygen species

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Weijie Jiang, Jie Bai, Xueyong Yang, Hongjun Yu, and Yanpeng Liu

). Suboptimal temperatures, which refer to day temperatures less than 20 °C and night temperatures less than 10 °C, are categorized as a chilling stress, one of the major environmental stresses affecting plant development and performance. Many tropical and

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Hui-Juan Zhou, Zheng-Wen Ye, and Ming-Shen Su

). Some authors considered that plants required more energy production under chilling stress ( Lee et al., 2009 ). Anaerobic respiration occurred, leading to the fast breakdown of fruit sugars at a specifically reduced level of O 2 , which was named as the

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Jack E. Staub, Vanessa S. Gordon, Philipp Simon, and Todd C. Wehner

backcross progeny is characterized by their response to chilling stress (5.5 h at 4 °C in 270 µmol·s −2 ·m −2 cool white lighting) at the first true-leaf stage under controlled environmental conditions. These lines provide chilling-tolerant genetic stocks