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Lijian Liang, Yanming Deng, Xiaobo Sun, Xinping Jia, and Jiale Su

chilling tolerance of anthurium by affecting the phenolic metabolism. It was proposed that NO induction under cold stress played a role in freezing tolerance through proline synthesis ( Zhao et al., 2009 ). As one of the osmotic regulators, proline also

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Shu Hsien Hung, Chun Chi Wang, Sergei Veselinov Ivanov, Vera Alexieva, and Chih Wen Yu

GSSG to regenerate GSH ( Kocsy et al., 2000a , 2000b , 2001 ). Therefore, inhibition of GSH synthesis by a specific inhibitor, BSO, could dramatically decrease the chilling tolerance of mung bean seedlings and maize ( Zea mays L.) ( Kocsy et al

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

LeARG1 and LeARG2 increased in tomato fruit during cold storage; these changes increased the chilling tolerance of fruit ( Zhang et al., 2010 ). CI is a physiological defect of many tropical and subtropical horticultural products that results in

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Mikal E. Saltveit

-shock on chilling-induced injury in excised asparagus tissue, and to use this knowledge to develop a heat-shock treatment that would increase the chilling tolerance of whole asparagus spears. Excised and aged 1-cm segments were initially used for four

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Zhanguo Xin and Paul H. Li

Exogenous proline and ABA can induce chilling tolerance. Whether there is any relationship between the proline and ABA in inducing chilling tolerance is not known. We attempted to elucidate their interrelationship by comparing the time course of proline and ABA induced chilling tolerance and of the uptake of proline and ABA in the cultured cells of maize (Zea mays L. Black Mexican Sweet). The uptake of proline was increasing continually during a 24 h culture at 28°C. However, the proline induced chilling tolerance became significant after 6 h treatment and reached maximum after 12 h. When cells were transferred to a ABA-containing medium the uptake of ABA in the cells reached almost plateau in 2 h period. The ABA induced chilling tolerance was insignificant at 6 h, became significant at 12 h, and reached maximum at 24 h. Although the rate of ABA induced chilling tolerance was slower than the rate of proline induced chilling tolerance, there was no any increase in endogenous free proline in the ABA treated cells. Statistical analysis indicates that there is no interrelationship between proline and ABA in the induction of chilling tolerance in maize. ABA induces specific proteins which may play essential role(s) in the development of chilling tolerance. None of these proteins was observed in proline treated cells. We concluded that the induction mechanisms of chilling tolerance between proline and ABA are independent in maize.

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M.E. Mangrich and M.E. Saltveit

Crops indigenous to the tropics and subtropics and some temperate crops suffer physiological injury when exposed to temperatures <12°C. Heat shock has induced chilling tolerance in a number of sensitive species (e.g., corn, cucumber, and tomato), but not in okra. To study this anomaly, we investigated the chilling sensitivity and heat shock response of a variety of Malvaceous species (i.e., cotton, hibiscus, kenaf, and okra). Seedlings with 8- to 12-mm long radicles were exposed to heat shock temperatures of 40 to 45°C for 2 to 12 minutes. Heat shocks were applied by two methods, floating the seeds in petri dishes on heated water and immersing the seeds in the heated water. The seedlings were held at 20°C for 2 hours after the heat treatments and then chilled at 2.5°C for 3 days. After chilling, seedlings were placed at 25°C for 3 additional days. The growth at 25°C was used as an assessment of chilling injury. Although there was a great deal of variability among the seedlings, a significant number of the okra and kenaf seedlings were more tolerant to chilling after heat shock: (i.e., more growth subsequent to chilling) compared to nonheat-shocked controls. More chilling tolerance was induced by the floating method than the immersion method. The response of cotton seedlings to heat-shock was variable, and the seedlings appeared damaged by even slight heat treatments (i.e., 4 minutes at 40°C). The variability in the capacity of heat-shocks to induce chilling tolerance in seedlings of Malvaceous species will be discussed.

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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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Paul H. Jennings and Ann Fitzpatrick

Four cucumber seed lines obtained from the Inst. of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, Beijing, China, were tested for chilling tolerance. Comparisons were made with `Poinsett 76', a commercially available cultivar from the United States. Seeds germinated at 25°C were exposed to 2°C for time periods up to 108 hr. Root injury was assessed by measuring subsequent root growth at 25°C at 72 hr after the chill. Electrolyte leakage measurements were taken on roots excised immediately after the chill. Total seedling root length and electrolyte leakage studies showed significant tolerance to chilling in the selections from China as compared to `Poinsett 76'. `Poinsett 76' seedling roots began to show stress after 72 hr of chill and were irreversibly damaged, with abortion of root tips, after 96 hr at 2°C. The China seed selections were more tolerant to a 96-hr chill and even at exposure times up to 108 hr only began to approximate chilling effects exhibited by `Poinsett 76' at 72 hr of treatment.

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Paul H. Jennings and Ann Fitzpatrick

Heat shock induction of chilling tolerance in cucumber seedlings is not blocked by inhibitors of protein synthesis. Treatment of germinating seeds with cycloheximide and actinomycin-D, prior to heat shock and chilling, does not block the heat shock induction of chilling tolerance, while the inhibitors alone promote chilling tolerance of seedling roots. To test whether the heat shock effect might be acting on proteases, two protease inhibitors (bestatin and PMSF) were tested for their ability to induce chilling tolerance. Although PMSF slowed germination, it still provided protection against chilling, but bestatin was much more effective.

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Hua Zhang and Paul H. Jennings

Heat shock was applied to 32-h-old cucumber seedlings before chilling at 2.5C. Two cultivars, `Poinsett 76' and `Ashley', with different chilling tolerances, were tested. Using root growth after chilling as a measure of chilling tolerance, three heat shock regimes were found to induce chilling tolerance in both cultivars, with the most effective and uniform induction by heat shock at 40C for 3 h. `Ashley', the more chilling tolerant cultivar, exhibited a greater response to heat shock induction of chilling tolerance than `Poinsett 76'. Protein samples from roots were subjected to SDS-PAGE. Three low molecular weight heat shock proteins accumulated to a greater extent in the protein profile of heat-shocked `Ashley' roots. No such increase was found in the `Poinsett 76' roots. The induction of low molecular weight HSPs are discussed in relation to the heat-shock induction of chilling tolerance.