DIA-based quantitative proteomic analysis on porcine meat quality at different chilling rates

The objective of this study was to evaluate the effects of chilling rate on porcine meat quality from the perspective of proteome using data independent acquisition(DIA)-based quantitative proteomic strategy. M. longissimus thoracis et lumborum(n = 9) was assigned randomly to the control group(3.72 ℃/h), very fast chilling-Ⅰ group(VFC-Ⅰ, 9.31℃/h) and VFC-Ⅱ group(14.43 ℃/h). The DIA was used to analyze the difference in proteins under different chilling rates. Results showed that tenderness was improved significantly in meat at the chilling rate of 14.43 ℃/h. Seventy-nine differential abundant proteins(fold change > 1.5, P < 0.05), including 46 up-regulated and 33 down-regulated proteins, were identified and mainly involved in carbon metabolism, pyruvate metabolism and proteasome pathways. These pathways indicated that VFC delayed cell metabolism and glycolysis by down-regulating the expression of metabolic enzymes. The tenderness was improved by up-regulating the expression of proteasome and m-calpain.

Research Progress and Outlook of Low Temperature Chilling Injury in Northeast China

Focused on the major agro-meteorological disaster in northeast China area—low temperature chilling injury,the research progresses of low temperature chilling injury in northeast China were reviewed systematically.The basic concepts which included the connotation and extension of chilling damage,the circulation characteristics and effect factors which formed summer low temperature in northeast China,the prediction,forecast and defense of low temperature chilling injury were summarized and done the outlook.

Effect of Polyamine Priming on Chilling Tolerance of Lolium perenne during Seed Imbibition

[Objective] This study aimed to investigate the effect of potyamine priming on physiological and biochemical variations of Lolium perenne embryos and seed germination. [Method] With annual Lolium perenne （Diamond T and Grazing-8000） as experimental materials, after priming with 0.5 mmol/L putrescine （Put）, spermidine （Spd） and spermine （Spm） for 24 h and chilling imbibition at 5 ℃ for 12, 24, 36 and 48 h, the effect of Put, Spd and Spm priming on chilling tolerance and germination ability of annual Lolium perenne seeds during imbibition was investigated. [Result] Put, Spd and Spm priming improved the activities of peroxidase （POD）, catalase （CAT）, superoxide dismutase （SOD） and ascorbate peroxidase （APX） and content of soluble protein content under low temperature stress, significantly in-creased the germination rate, and shortened the average germination duration. After chilling imbibition for 48 h, compared with the control, the average germination rate of annual Lolium perenne seeds was improved by 15.5% and 12.0% after Put, Spd and Spm priming, and the average germination duration was shortened by 1.21 and 1.14 d. During seed imbibition, the chilling tolerance of Grazing-8000 was stronger than that of Diamond T. Overall, Put, Spd and Spm treatment could increase the chilling tolerance of annual Lolium perenne seeds during imbibition, and improve the germination ability of seeds under low temperature stress. [Conclusion] Results of this study provided theoretical basis for the application of seed priming technology in the production of annual ryegrass.

Analysis and Evaluation Indicator Selection of Chilling Tolerance of Different Cotton Genotypes

[Objectivc] This study aimed to investigate the chilling tolerance of seedlings of different cotton genotypes and screen appropriate indicators for assess- ing chilling tolerance, to establish reliable mathematical evaluation model for chilling tolerance of cotton, thus providing theoretical basis for breeding and promoting new chilling-tolerant cotton germplasms and large-scale evaluation of chilling tolerance of cotton varieties. [Method] Fifteen cotton varieties （lines） were used as experimental materials. The photosynthetic gas exchange parameters, chlorophyll fluorescence ki- netic parameters, chlorophyll content, relative soluble sugar content, malonaldehyde content, relative proiine content, relative conductivity and other 12 physiological indi- cators of seedling leaves under low temperature treatment （5 ℃, 12 h） and recovery treatment （25 ℃. 24 h） were determined; based on the chilling tolerance coefficient （CTC） of various individual indicators, the comprehensive evaluation of chilling toler- ance was conducled by using principal component analysis, hierarchical cluster anal- ysis and stepwise regression analysis. [Result] The results showed that the 12 indi- vidual physiological indicators could be classified into 7 independent comprehensive components by principal component analysis; 15 cotton varieties （lines） were clus- tered into three categories by using membership function method and hierarchical cluster analysis; the mathematical model for evaluating chilling tolerance of cotton seedlings was established： D =0.275 -0.244Fo1 ＋0.206Fv/Fm1＋0.326g,%-0.056SS ＋ 0.225MDA＋O.O38REC （FF=0.995）, and the evaluation accuracy of the equation was higher than 94.25%,0. Six identification indicators closely related to chilling tolerance were screened, including Fo,, Fv/Fm1, Seedling leaves of cotton varieties （lines） gs2, SS, MDA, and REC. [Conclusion] with high chilling tolerance are less dam- aged under low temperature stress, and are able to maintain relatively high photo- synthetic electron transport capacity and high stomatal conductance after recovery treatment, which is contributed to gas exchange and recovery of photosynthetic ca- pacity. Determination of the six indicators under the same stress condition can be adopted for rapid identification and prediction of the chilling tolerance of other cotton varieties, which provides basis for the breeding, promotion, identification and screen- ing of chilling tolerant germplasms.

AtpH Is a Chilling-Repressed Gene in Rice

A chilling-repressed cDNA fragment was cloned from rice ( Oryza sativa L.) seedlings by reverse transcription-polymerase chain reaction (RT-PCR) differential display. Database comparison of the cDNA sequence is identical to atpH encoded by rice chloroplast genome. Northern hybridization showed that its RNA transcript was reduced greatly on the first day and fully inhibited after 2 d of chilling treatment.

Study on Chilling Requirement of Different Fruit Branch of a Sweet Cherry Cultivar ‘Hongmanao'

With ＇Hongmanao＇, a sweet cherry cultivar from central Shanxi Province, as the experimental material, the chilling requirements of different types of fruit branches （including mixed fruit branch, long fruit branch, medium fruit branch, short fruit branch and blossom fruit branch） were studied by the 0-7.2 ℃ model in a solar greenhouse during 2012-2013. In the greenhouse, the fruit branches of ＇Hongmanao＇ were cultured in water in a thermostatic environment. The results showed that the chilling requirement of leaf buds of ＇Hongmanao＇ was lower than that of its flower buds; and the chilling requirements of the five types of fruit branches ranked as blossom fruit branch＇s〈short fruit branch＇s〈medium fruit branch＇s〈long fruit branch＇s〈mixed fruit branch＇s,

Effect of Delay Chilling on μ-calpain Activities and the Tenderness of Bovine M. longissimus

μ-calpain activities and shear force values of bovine M. longissimus from Chinese Yellow crossbred bulls were analyzed,and the effect of delay chilling on μ-calpain activities and the tenderness of beef during postmortem aging were studied. The results showed that delay chilling significantly improved μ-calpain activities (P<0.05) and enhanced the tenderness of bovine M. longissimus during earlier aging periods compared with conventional chilling. But in later aging periods,delay chilling weakened the effect on the tenderness of beef because of premature consumption of μ-calpain. The experiment results confirmed that delay chilling improved the rate of postmortem aging of beef and remarkably enhanced the tenderness of beef through the effect of delay chilling on μ-calpain activities.

Methyl Jasmonate Reduces Chilling Injury and Maintains Postharvest Quality in Peaches

Zhaohui peaches(Prunus persica Batsch)were treated with 0(CK), 1, 10 or 100 μmol L-1 methyl jasmonate(MeJA)vapor at 20℃ for 24 h before stored at 0℃ for 35 d. The untreated fruits showed chilling injury(CD symptoms after 4 wk of storage, as indicated by increased fruit firmness and reduced ex-tractable juice, which is referred as leatheriness. Treatment with 1 and 10 μmol L-1 MeJA promoted normal ripening and softening, maintained higher levels of extractable juice, titratable acidity, pectinesterase(PE)and polygalacturonase(PC)activities, inhibited increases in fruit fresh weight loss, decay incidence, electrolyte leakage and MDA content, and improved color development, thereby preventing chilling injury symptoms development and maintaining edible quality. MeJA treatment also delayed the climacteric rise in respiratory rate, but promoted ethylene production during the later period of cold storage, suggesting that ethylene may involve in CI development of peaches. These results indicate that 1 and 10 μmol L-1 MeJA treatments could be used to reduce CI development and decay incidence in peaches.

Water relations and an expression analysis of plasma membrane intrinsic proteins in sensitive and tolerant rice during chilling and recovery

A symptom of chilling injury is development of water deficit in shoots, resulting from an imbalance of water transport and transpiration. In this work, two rice varieties （Oryza sativa L. var. Wasetoitsu and Somewake） seedlings were chilled at 7 ℃, followed by recovery at 28 ℃. Based on the growth phenotype and electrolyte leakage tests, Somewake was shown to be a chilling-tolerant variety, and Wasetoitsu a chilling-sensitive one. The chilling stress reduced markedly the relative water content （RWC） of leaves, accumulative transpiration and osmotic root hydraulic conductivity （Lp） in both varieties. But when retumed to 28 ℃, the water relation balance of Somewake recovered better. The mRNA expression profile of all the 11 plasma membrane intrinsic proteins （PIPs）, a subgroup of aquaporins, was subsequently determined by real-time reverse transcription （RT）-PCR with TaqMan-minor grove binder （MGB） probes derived from rice var. Nipponbare during chilling treatment and recovery. Most of the PIP genes was down-regulated at the low temperature, and recovered at the warm temperature. The relative expression of some PIPs in both Somewake and Wasetoitsu decreased in parallel during the chilling. However during the recovery, the relative expression of OsPIP1;1, OsPIP2;1, OsPIP2;7 in shoots and OsPIP1：1, OsPIP2：1 in roots were significantly higher in Somewake than Wasetoitsu. This supports the role of PIPs in re-establishing water balance after chilling conditions. We discuss the diversified roles played by members of the aquaporin PIP subfamily in plant chilling tolerance depending on aquaporin isoforms, plant tissue and the stage of chilling duration.

Melatonin treatment induces chilling tolerance by regulating the contents of polyamine,γ-aminobutyric acid,and proline in cucumber fruit

The mechanism of melatonin(MT)induced chilling tolerance in harvested cucumber fruit was investigated at commercial maturity.In this study,cucumber fruits were treated with 100μmol L^(-1) MT at 4℃ and 90% relative humidity for 15 d of storage.In comparison with the control,cucumber treatment with MT resulted in reduced chilling injury(CI),decreased electrolyte leakage and enhanced firmness.The fruits treated with MT showed higher chlorophyll contents in storage conditions with suppressed chlorophyllase enzyme activity.MT treatment increased arginine decarboxylase(ADC)and ornithine decarboxylase(ODC)enzyme activities.Moreover,enhanced expression of the Cucumis sativus ADC(CsADC)and C.sativus ODC(CsODC)genes resulted in the accumulation of polyamine contents.Similarly,proline levels exhibited higher levels among treated fruits.Meanwhile,the proline synthesizing enzymes △1-pyrroline-5-carboxylate syntheses(P5CS)and ornithine aminotransferase(OAT)were significantly increased,while a catabolic enzyme of proline dehydrogenase(PDH)activity was inhibited by treatment.In addition,MT induced expression of C.sativus OAT(CsOAT)and C.sativus P5CS(CsP5CS)genes.Cucumber fruits treated with MT also exhibited higher γ-aminobutyric acid(GABA)content by enhanced GABA transaminase(GABA-T)and glutamate decarboxylase(GAD)enzyme activities and a higher C.sativus GAD(CsGAD)gene expression.To sum up,the results show that MT treatment enhanced chilling tolerance,which was associated with the regulation of polyamines,as well as proline and γ-aminobutyric acid.

Photosynthesis, chilling acclimation and the response of antioxidant enzymes to chilling stress in mulberry seedlings

This study investigates the effects of cold-acclimation in conferring chilling tolerance in seedlings of the mulberry(Morus alba) variety ‘Qiuyu’. Changes in photosynthesis and antioxidant enzymes in chilling acclimatized(CA), and non-acclimatized(NA) seedlings were recorded during chilling stress(3 °C) and a recovery period(25 °C) each for 3 days. The results showed that CA plants had higher net photosynthetic rates(P_n), stomatal conductance(G_s), and maximum photochemical efficiency of photosystem Ⅱ(F_v/F_m) in response to chilling stress compared to NA. The seedlings maintained the same trends during the recovery stage. The responses of Q_A reduction degree (1-q_P) and prime electronic transfer rates(F_o) were lower in acclimatized than in non-acclimatized seedlings. Low-temperature acclimation and chilling stress also caused an increase in leaf proline and soluble sugar contents. Leaf malondialdehyde levels were significantly lower while ascorbate peroxidase(APX) activity was significantly higher in acclimatized seedlings, suggesting that elevated osmolytes and APX confer resistance to chilling temperatures. In this study on the response of mulberry seedlings to chilling stress, we also looked at the recovery process. The response to chilling determines whether mulberry leaves can survive under cold temperatures, while the recovery process determines whether photosynthesis can recover as soon as possible to avoid any secondary damage.

Response of leaf photosynthetic characteristics of Syringa oblata and Syringa reticulata var.mandshurica to chilling stress

Syringa species not only have good ornamental properties but also play an important role in the landscaping and environmental purification of cities.To investigate the chilling stress resistance of Syringa oblata Lindl.and Syringa reticulata var.mandshurica and provide theoretical grounds for the practical cultivation of Syringa species,in vitro leaves were used to study photosynthetic gas exchange parameters and chlorophyll fluorescence parameters.After nine hours of chilling,decreasing rates of net photosynthesis,stomatal conductance,and transpiration in S.reticulata var.mandshurica leaves were significantly greater than that of the S.oblata,while intercellular CO2 concentrations in S.oblata leaves were higher than those in S.reticulata var.mandshurica.The quantum yield of PSII reaction center(APSII)declined in S.reticulata and light capture efficiency(Fv 0/Fm 0)was stable.However,reduction percentages of Fv 0/Fm 0,APSII,and Fv/Fm in S.oblata were significant higher than those of S.reticulata var.mandshurica.After nine hours of chilling,the relative variable fluorescence of VJ and VI of S.oblata increased and the increasing rate of VJ was greater than VI.In contrast,the change of VJ and VI in S.reticulata var.mandshurica leaves was relatively small.This suggests that chilling primarily damaged the electron transport process of QA to QB at the receptor site of the PSII reaction center.Photosynthetic capacity of S.oblata was more sensitive to chilling stress compared to S.reticulate var.mandshurica,which the limitations were mainly due to non-stomatal factors such as the decrease in electron transport efficiency,activity in the PSII reaction center,and the destruction of the photodamage defense system.

Accumulated chilling hours during endodormancy impact blooming and fruit shape development in peach(Prunus persica L.)

Winter chill is essential for the growth and development of deciduous species. To understand the relationship between accumulated chilling hours during endodormancy and blooming and fruit shape development, we controlled chilling hours and investigated their effects on blooming date and fruit shape of peaches. The results showed that the number of days to full bloom date and the heat requirement for blooming were negatively correlated with accumulated chilling hours. Accumulated chilling hours were significantly negatively correlated with fruit shape index and fruit tip lengths, suggesting that the number of chilling hours affect the fruit shape development. Fewer accumulated chilling hours may be the major reason for longer fruit shape and protruding fruit tips. In conclusion, our results indicate specifically that decreased winter chilling hours can delay the bloom date and may lead to aberrant fruit shape development in peaches. Our study provides preliminary insights into the response of temperate fruit species to global climate change.

Exogenous melatonin improves the chilling tolerance and preharvest fruit shelf life in eggplant by affecting ROS-and senescence-related processes

Low temperature is the most common abiotic stress factors during the eggplant cultivation in solar greenhouses.Melatonin plays important roles in plant resistance to low temperature.However,the role of melatonin in regulating chilling tolerance and extending the preharvest shelf life of eggplant fruits is still unknown.In this study,we investigated the effects of exogenous melatonin on eggplant plants and fruits in response to low temperature.Under simulated low-temperature conditions,exogenous melatonin significantly relieved the chilling symptoms of seedlings by reducing reactive oxygen species (ROS) and malondialdehyde (MDA) levels and relative leakage rates.These reductions were caused by higher superoxide dismutase (SOD) and catalase (CAT) activities and increased endogenous polyamine and melatonin levels compared with those in untreated seedlings.Notably,the expression levels of SOD,CAT1/2,and polyamine synthesis genes (ADC and ODC) were also increased by 100μmol·L~(-1)melatonin,as well as those of genes involved in melatonin synthesis (TDC,T5H,SNAT,ASMT,and COMT) and cold regulation (COR1,CBFa/b,and ZAT2/6/12).To further investigate the effects of melatonin on eggplant leaves and fruits under natural low temperature conditions,100μmol·L~(-1)melatonin was sprayed on the functional leaves at three days before commodity maturation.Melatonin significantly alleviated chilling injury in the leaves and pericarp and extended the preharvest shelf life of the fruit by increasing the expression of COR1,CBF,ZAT2/6/12,and API5 and decreasing the expression of senescence-related genes (NCED1/2 and SAG12).Therefore,100μmol·L~(-1)melatonin improved chilling tolerance and fruit shelf life by upregulating ZAT2/6/12 to affect ROS-and senescence-related processes,which provides a reference for alleviating cold stress and extending the preharvest fruit shelf life in eggplant.

Effects of Exogenous Silicon on the Activities of Antioxidant Enzymes and Lipid Peroxidation in Chilling-Stressed Cucumber Leaves

In order to increase vegetable productivity by improving environmental conditions, this article investigates the effects of exogenous silicon on the activities of major antioxidant enzymes and on lipid peroxidation under chilling stress, and it examines whether silicon-induced chilling tolerance is mediated by an increase in antioxidant activity. Cucumis sativus cv. Jinchun 4 was hydroponically cultivated to the two-leaf stage, at which point seedlings were watered with different concentrations of silicon (0, 0.1 and 1 mmol L^-1) and separately exposed to normal (25/18℃) or chilling (15/8℃) temperatures for six days under low light (100μmol m^-2 s^-9. Data were collected from the second leaves on the percentage of withering and the levels of endogenous silicon, malondialdehyde (MDA), hydrogen peroxide (H202), superoxide radical (O2^.-), superoxide dismutase (SOD, EC 1.15.1.1), glutathione peroxidase (GSH-Px, EC 1.11.1.9), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), glutathione reductase (GR, EC 1.6.4.2), reduced glutathione (GSH) and ascorbate (AsA). Compared to normal temperatures, chilling resulted in partially withered leaves and increased MDA content. When 0.1 or 1 mmol L^-1 exogenous silicon was combined with chilling, the withering of the cucumber leaves was reduced relative to the original chilling treatment, while the endogenous silicon content was increased, antioxidants such as SOD, GSH-Px, APX, MDHAR, GR, GSH, and AsA were more active, and the levels of H2O2, O2^.-, and MDA were lower. We propose that exogenous silicon leads to greater deposition of endogenous silicon and thereby increases antioxidant activities and reduces lipid peroxidation induced by chilling.

Impact of chilling accumulation and hydrogen cyanamide on floral organ development of sweet cherry in a warm region

The microscopic investigation of the floral development of sweet cherry（Prunus avium L. cv. Hongdeng） from a warm winter climate（Shanghai） and cold winter climate（Tai＇an, Shandong Province, China） was conducted to explore the reason of low fruit set. The effect of hydrogen cyanamide（HCN） on floral development under warm winter conditions was also investigated. Trees grown in Shanghai with insufficient chilling accumulation exhibited little difference in the progression of microspore development compared to trees in Tai＇an that accumulated adequate chilling, but showed substantial delays in ovule and embryo sac development. The growth of nucelli did not proceed beyond the macrospore mother cell and macrospore stages with abortion rates of 13, 15 and 45% by 6, 3 and 0 d before full bloom, respectively. These abnormalities in the ovule and embryo sac in the Shanghai-grown trees were eliminated by HCN application. These results suggest that chilling regulates the development of female floral organs in winter dormancy; therefore, insufficient chilling accumulation, causing abnormality of the female floral organs, restricts the cultivation of sweet cherry in warm winter regions. Interestingly, HCN application, which decreased the chilling requirements for Hongdeng, may be a potential strategy for sweet cherry cultivation in warm winter regions.

Thermal-responsive genetic and epigenetic regulation of DAM cluster controlling dormancy and chilling requirement in peach floral buds

The Dormancy-associated MADS-box(DAM)gene cluster in peach serves as a key regulatory hub on which the seasonal temperatures act and orchestrate dormancy onset and exit,chilling response and floral bud developmental pace.Yet,how different temperature regimes interact with and regulate the six linked DAM genes remains unclear.Here,we demonstrate that chilling downregulates DAM1 and DAM3–6 in dormant floral buds with distinct patterns and identify DAM4 as the most abundantly expressed one.We reveal multiple epigenetic events,with tri-methyl histone H3 lysine 27(H3K27me3)induced by chilling specifically in DAM1 and DAM5,a 21-nt sRNA in DAM3 and a ncRNA induced in DAM4.Such induction is inversely correlated with downregulation of their cognate DAMs.We also show that the six DAMs were hypermethylated,associating with the production of 24-nt sRNAs.Hence,the chilling-responsive dynamic of the different epigenetic elements and their interactions likely define distinct expression abundance and downregulation pattern of each DAM.We further show that the expression of the five DAMs remains steadily unchanged or continuously downregulated at the ensuing warm temperature after chilling,and this state of regulation correlates with robust increase of sRNA expression,H3K27me3 and CHH methylation,which is particularly pronounced in DAM4.Such robust increase of repressive epigenetic marks may irreversibly reinforce the chillingimposed repression of DAMs to ensure flower-developmental programming free from any residual DAM inhibition.Taken together,we reveal novel information about genetic and epigenetic regulation of the DAM cluster in peach,which will be of fundamental significance in understanding of the regulatory mechanisms underlying chilling requirement and dormancy release,and of practical application for improvement of plasticity of flower time and bud break in fruit trees to adapt changing climates.

Higher Chilling-Tolerance of Grafted-Cucumber Seedling Leaves upon Exposure to Chilling Stress

The roots of figleaf gourd （Cucurbita ficifolia, as rootstock） could improve the resistance of cucumber plants （Cucumis sativus L. cv. Jinyan 4, as scion） to low temperature. In this experiment, the root activity and photosynthetic activity of photosystems in the own-rooted and grafted-cucumber plants were studied at chilling temperature （4℃） under low irradiance （100 μmol m^2 s^-1 PFD）. Compared with dark adaptation seedlings, the chlorophyll a fluorescence transient curve and the oxidizable P700 （P700＋） of both the own-rooted and grafted seedlings decreased, and PS2 and PS1 of the own-rooted seedling leaves were more inhibited than that of grafted ones at the end of chilling stress. The reduced triphenyltetrazolium chloride （TTC）, which was used to reflect the root activity, kept stable in grafted seedling roots at the end of chilling stress, while it decreased noticeably in the own-rooted seedling roots. These results implied that the root system activity of the grafted seedling roots was higher than that of the own-rooted ones. Superoxide dismutase （SOD） activity was higher in both the grafted seedling roots and leaves than that in own-rooted seedlings at both room temperature and chilling temperature. Upon exposure to chilling stress, the malondialdehyde （MDA） content, which reflects the degree of lipid peroxidation, increased markedly in the own-rooted seedling roots and leaves and kept stable in the grafted-cucumber seedlings.

Reduction of Chilling Injury and Ultrastructural Damage in Cherry Tomato Fruits After Hot Water Treatment

The effects of hot water treatment in alleviating chilling injury and reducing ultrastructural damage of mature-green cherry tomatoes （Lycopersicun esculentum cv. cerasiform Alef） were investigated. Mature-green cherry tomato fruits were treated in water at 40℃ or 45℃ for 5 min or 15 min, and then stored at 5℃ for 19 days followed by ripening at 20℃. Water treatment at 40℃ for 15 min increased tolerance of cherry tomato fruits to chilling stress, indicating as low outbreak of skin lesion, high color a＊ value, and low electrolyte leakage. Treated fruits showed typical climacteric respiration and developed normal red color with chlorophyll degradation and lycopene accumulation during ripening, while fruits without treatment failed to develop red color and suffered skin lesion. After 19 days of chilling, heated fruits showed the conversion of chloroplast to chromoplast with the disappearance of thylakoids. Mitochondria and other cell organelles were not adversely affected in treated fruits. However, ultrastructures in pericarp cells in control fruits severely damaged with extensive disorganization of cytoplasm, swelled chloroplasts, distorted and unstacked thylakoids. Chloroplast was the first and most severely impacted organelle by chilling stress. Hot water treatment （40℃ for 15 min） before storage alleviated chilling injury in cherry tomato fruits. The results suggest that chilling injury is related with the damage of cell structure under chilling stress.

Responses of Antioxidant Enzymes to Chilling Stress in Tobacco Seedlings

Chilling is one of the major abiotic stresses limiting yield and quality of many important crops. For better understanding of chilling stress responses in tobacco （Nicotiana tabacum）, growth rate and antioxidant enzymes of seedlings in 2 tobacco cultivars, viz., MSk326 （chilling sensitive variety） and Honghuadajinyuan （HHDJY, chilling tolerant variety） at chilling temperature （5℃） were studied. The results showed that the relative growth rate in chilling period to that in recovery period was significantly higher in roots than that in shoots for both cultivars, suggesting that shoots growth was more easily affected by chilling stress. Chilling stress increased peroxidase （POD） activity and reduced superoxide dismutase （SOD） activity in shoots of HHDJY, and catalase （CAT） activity was little affected. In the roots of HHDJY, chilling stress increased SOD and CAT activities, and had little effect on POD activity. For MSk326, chilling treatment increased SOD activity in shoots and declined CAT activity in roots. MDA concentration in both varieties was increased under the chilling stress, while it was decreased after seedlings were recovered growth for 4 d at normal temperature （25℃）. It showed that tobacco seedlings might have the capacity of recovering from chilling injury for a short term, The relationship between the growth rate and antioxidant enzyme activity was analyzed by stepwise regression. It was found that there was a close relationship between relative growth rate of tobacco seedlings and CAT activity under chilling stress condition and regression equations containing CAT could be used in predicting seedling growth rate of tobacco under chilling stress condition.