Cold acclimation in white clover subjected to chilling and frost: Changes in water and carbohydrates status

The effect of cold acclimation on the water status and the fate of carbohydrates was studied in white clover (Trifolium repens L., cv Huia) subjected to chilling and/or freeze-thaw cycles. Treatments were applied in a controlled environment, with a constant photoperiod, for 6 weeks to plants either acclimated or non-acclimated to low temperature.

Cold acclimated plants had a higher concentration of starch in the stolons at the end of the acclimation period than non-acclimated plants (54 vs. 15 mg g⁻¹ DW). During the experiment, the leaves of cold acclimated plants subjected to frosts maintained a higher relative water content (RWC) than did leaves of plants not acclimated for which we observed a strong dehydration of 80%.

Under chilling, cold acclimated plants demonstrated an osmotic adjustment. We showed that only 30–40% of the variation of the osmotic potential was explained by variation in free sugar concentration, suggesting that compounds other than carbohydrates participated in the osmotic regulation.

Chilling increased the carbohydrate content and frost decreased the starch concentration in non-acclimated plants only.

We showed in white clover that the cold acclimation contributed to frost and chilling tolerance by the maintenance of the hydration of tissues. We demonstrated that osmotic adjustment was not completely explain by the accumulation of free sugars.     

Assessment of chilling injury during storage: chlorophyll fluorescence characteristics of chilling-susceptible and triazole-induced chilling tolerant basil leaves

Chlorophyll (Chl) fluorescence analysis by pulse-amplitude modulation (PAM) measurements was performed to assess the extent of chilling injury (CI) in stored sweet basil (Ocimum basilicum L.) leaves. Changes in three photosynthetic characteristics, in relation to visible CI rating, were monitored in leaves following modification of their chilling susceptibility by varying storage temperature and duration in two basil cultivars, or by soil application of triazole. Basil leaves developed severe or moderate visible symptoms of CI after 4 days of storage at 4 or 8 °C, respectively, but remained undamaged when stored at 12 °C. The chilling-dependent changes obtained in the ratios of variable to maximal fluorescence (F_v/F_m), represented chilling sensitivity rather than membrane damage. The photochemical quenching coefficient (qP) was unaffected by low temperatures and did not seem to be correlated with CI. On the other hand, changes in the non-photochemical quenching coefficient (qNP) were positively correlated with the appearance of visual CI symptoms in leaves of the two cultivars at all storage temperatures and durations. Similarly, the chilling-alleviating effect of triazole was accompanied by a corresponding reduction in the chilling-induced decrease of qNP. Therefore, qNP may be associated with an irreversible transition step in the CI process, which precedes the appearance of visual symptoms. As such, changes in qNP may provide a suitable, rapid and non-destructive criterion for estimation of chilling damage in green tissues.     

Effect of short term cold stress on rice seedlings

A method was developed for exposing riceseedlings to low temperatures for shortperiods. These seedlings were from 70F₉ inbred lines derived originallyfrom a hybrid of a salt tolerant cultivar,which provided a source of resistance toabiotic stress, and a non salt tolerantcultivar as the other parent. Seedlingswere grown hydroponically in a warm growthroom then placed in the air above afreezing bath for 6 hours at –0.2 ^°C,–1.0 ^°C or –2.0 ^°C beforereturning them to the growth room for a7–10 day period. Seedling survival in theinbred lines of rice was compared afterexposure to these temperature treatments toidentify the presence of low temperaturetolerance. An average survival of 93%occurred 7days after exposures to –0.2, and–1.0 ^°C and a survival of 35% afteran exposure of –2.0 ^°C. The non-salttolerant parent cultivar was killed byexposure to –2.0 ^°C but the salttolerant parent survived. The effect of lowtemperature exposure was examined in moredetail in lines selected for lowtemperature tolerance and susceptibility.Alterations to the total leaf proteinprofile, including fragmentation ofRubisco, were observed in these lines butno obvious difference was detected betweensusceptible and tolerant individuals.     

Effect of prolonged cold storage on the sensory quality of peach and nectarine

To maintain peach and nectarine quality after harvest, low temperature storage is used. Low temperatures induce physiological disorders in peach, but the effect of cold storage on the sensory quality of the fruit before it is damaged by chilling injury syndrome remains unclear. To evaluate the cold storage effect on the sensory quality two peach cultivars (’Royal Glory’ and ‘Elegant Lady’) and two nectarines (’Ruby Diamond’ and ‘Venus’) were harvested at a standardized firmness level and subjected to quality evaluations and sensory analysis at harvest and after storage at 0 °C for 35 d. For both time points, a supplementary ripening followed such that homogeneous flesh firmness and suitability for consumption was achieved.The fruit segregation through the Durofel firmness (DF), evaluated using a non-destructively method (Durofel device), allowed the formation of a uniform group of fruit in terms of flesh firmness (FF), showing scores between 45.1 and 55.9 N. The average FF in fruit ripened immediately after harvest was 22.9 N and 25.6 N in fruit ripened after cold storage for 35 d.The “acceptability” of fruit is highly correlated with “aroma”, “sweetness”, “juiciness”, “texture” and “flavor”. Only the “acid taste” parameter had no significant correlation with “acceptability” or with the other parameters evaluated.It is possible to conclude that the sensory quality and acceptability of peach and nectarine are characteristic of each cultivar and change, depending on the time elapsed after harvest. In general, it was confirmed that nectarine cultivars have a more consistent quality than peach cultivars.     

Effect of salicylic acid treatment on alleviating postharvest chilling injury of ‘Qingnai’ plum fruit

The effects of salicylic acid (SA) treatment on chilling injury, disease incidence, electrolyte leakage, malondialdehyde (MDA) content, respiration rate and ethylene production, polyphenol oxidase (PPO) and peroxidase (POD) activities, and polyamine (PA) content of ‘Qingnai’ plum fruit were examined. Chilling injury, disease incidence, electrolyte leakage, MDA content, respiration and ethylene production of control fruit increased after about 15-30 days cold storage. Chilling injury promoted PPO and POD activities which were associated with fruit flesh browning. Accompanied by a polyamine content increase, chilling injury was positively correlated with putrescine and spermine contents in control fruit. Suppression of chilling injury by SA was associated with reducing leakage, MDA content, delayed activities of PPO and POD, and enhanced PA accumulation. SA treatment delayed the onset of the climacteric peak of respiration, and also inhibited respiration and ethylene production. The results suggest that SA treatment may be used commercially to control chilling injury in ‘Qingnai’ plum fruit during cold storage.     

间歇加温缓解冷藏甜椒冷害的研究

有关果蔬贮运过程的冷害大多是从恒温贮藏角度加以研究.木文根据东北地区的气候特点,从节省能源、延缓冷害的角度研究了冷藏甜椒对间歇加温的生理反应,并根据贮藏过程中的外观变化分析说明了间歇加温措施的贮藏效果及影响因素.     

烟草乙烯反应突变体的抗冷性及机理分析

为了深入研究乙烯在植物抵抗逆境胁迫中的作用,以烟草为模式植物,利用幼苗对外源乙烯的"三重反应",筛选得到了40多个乙烯不敏感突变体,其中多数突变体具有较强的抗冷性;从中选取4个突变体株系,对它们耐受低温胁迫的生理基础和作用机理进行了分析。结果表明,低温(0℃)胁迫下,烟草乙烯不敏感突变体的电解质渗透率显著低于野生型,而抗氧化酶活性(POD、SOD)以及过氧化氢酶(CAT)活性都高于野生型,说明突变体具有抵抗低温胁迫的优势生理基础。进一步研究发现,低温(0℃)胁迫下,烟草突变体中冷诱导基因Nt CBFs和Nt COR47呈现高水平表达,乙烯信号传导途径中下游基因ERFs的表达也发生显著变化。这些研究为烟草乙烯不敏感突变体株系具有较强的抗冷性提供了直接的分子证据。     

缓慢降温对石榴果实冷害发生及生理变化的影响

对缓慢降温处理后石榴果实在冷害温度下的生理反应进行了研究,旨在为石榴果实采后保鲜提供理论依据。以新疆大籽石榴为试材,研究了0℃低温胁迫及缓慢降温对石榴果实采后生理的影响结果表明,与0℃的低温相比,缓慢降温处理减缓石榴果皮细胞膜透性的升高以及膜脂质过氧化物丙二醛的积累,抑制了多酚氧化酶活性的增加及减少了酚类物质的氧化,明显推迟和减轻石榴果实冷害症状的发生,减轻了果皮的褐变,保持果实品质。     

Growth and development of maize (Zea mays L.) seedlings under chilling conditions in the field

Maize inbred lines of different origins were grown in spring (for 2 years at early and usual sowing dates) in northeastern Switzerland (latitude 47°27′ N; 550 and 720 m a.s.l.) until five to six leaves were fully developed. Averaged over all observation periods, the group of inbred lines used in hybrids for cool temperate regions (CT lines) showed better heterotrophic and autotrophic shoot growth and faster development than the group of lines adapted to warm tropical regions (CS lines). The more efficient autotrophic shoot growth of CT lines was expressed by higher rates of relative growth (RGR) and relative leaf area expansion (RLGR) and was related to a higher net assimilation rate (NAR) and a lower leaf area ratio (LAR). CT lines had better radiation use efficiency (RUE), higher rates of net photosynthesis (P_N), and lower specific leaf area (SLA) than CS lines. The greater RGR and RLGR of CT line Z 7 as compared to the CS line Penjalinan were related to a higher assimilation rate but not to a better use of carbohydrates; in Z 7 the balance between assimilation production and use resulted in a greater accumulation of soluble carbohydrates and starch. Genotypic variability existed for most growth parameters and was greatest for NAR. Growth responses of inbred lines under field conditions in spring were influenced mainly by temperature. Of all parameters, NAR was correlated best with temperature. Under decreasing temperature, RGR, RLGR, the rate of leaf appearances (RLA) and NAR decreased, whereas LAR, leaf area partitioning (LAP), and SLA increased slightly. The soluble carbohydrate content of Z 7 and Penjalinan also increased. RUE showed the best correlation with the daily minimum air temperature. Within the temperature limits of this experiment, no significant interactions were found between inbred line and temperature.     

Overexpression of cold-inducible wheat galactinol synthase confers tolerance to chilling stress in transgenic rice

Galactinol synthase (GolS) is considered to be a key regulator of the biosynthesis of Raffinose family oligosaccharides (RFOs). Accumulation of RFOs has been reported to play a role in protection against abiotic stresses. We identified two cDNAs encoding galactinol synthase from wheat (Triticum aestivum L.), which we designated as TaGolS1 and TaGolS2. Expression of the two TaGolS genes was induced by cold stress but not by drought, heat stress or ABA treatment in wheat. We generated transgenic lines of rice (Oryza sativa L.) constitutively overexpressing TaGolS1 or TaGolS2. These transgenic plants accumulated significantly higher levels of galactinol and raffinose than did wild-type plants and exhibited enhanced cold-stress tolerance. The results demonstrate the involvement of galactinol and raffinose in the development of chilling stress in rice and indicate that the genetic modification of the biosynthesis of RFOs by transformation with GolS genes could be an effective method for enhancing chilling-stress tolerance in rice.     

Characterization of chilling injury in Heliotropium arborescens and Lantana camara cuttings

Simulated low-temperature shipment of Heliotropium arborescens and Lantana camara cuttings inflicted chilling injury, which was manifested in increased ion leakage in both species. Morning-harvested cuttings of both Lantana and Heliotropium were more sensitive to chilling temperatures than noon-harvested cuttings. However, this difference was expressed only during the summer in Lantana, but both in the winter and summer in Heliotropium cuttings. These results suggest that the chilling injury that occurs during shipment might be alleviated in both species by avoidance of early morning picking of cuttings.

Chilling injury in Lantana was associated with increases in reactive oxygen species (ROS) levels and ethylene production rate. On the other hand, in Heliotropium cuttings ROS levels were increased and the ethylene production rate was reduced after storage at all simulated shipment temperatures. Our results may indicate that different mechanisms of chilling injury exist in Lantana and Heliotropium.     

Nitric oxide participates in the regulation of LeCBF1 gene expression and improves cold tolerance in harvested tomato fruit

Nitric oxide (NO) is an important signal molecule involved in numerous plant responses to biotic and abiotic stress. C-repeat/dehydration-responsive element (CRT/DRE)-binding factors (CBFs) play a prominent role in cold response regulation. To investigate the relationship between NO and the CBF pathway during cold stress, tomato (Solanum lycopersicum cv. Lichun) fruit were treated with the NO donor (sodium nitroprusside, SNP) and nitric oxide synthase (NOS) inhibitor (N (omega)-nitro-l-arginine, l-NNA) before storage at 2 °C. Treatment with 0.02 mM SNP decreased the chilling injury (CI) index, whereas l-NNA treatment increased the appearance of chilling symptoms. NO content in fruit following SNP treatment was higher, while malondialdehyde (MDA) content and ion leakage were lower than that in water- and l-NNA-treated fruit. The relative expression of LeCBF1, measured by q-RTPCR, in SNP-treated fruit was higher than that in l-NNA-treated and control fruit after cold storage for 0.5 and 4 h. These results suggest that SNP treatment protects tomatoes from cold injury by inducing NO accumulation and expression of LeCBF1. NOS activity may play a role in NO accumulation associated with cold tolerance.     

Influence of hot water treatment on brown rot of peach and rapid fruit response to heat stress

Recent results on hot water as an alternative treatment open a new perspective in disease incidence reduction. In the present work peach fruit were wounded, inoculated with conidia of Monilinia laxa and 15 min, 3, 6, 12, 24 and 48 h after inoculation treated by dipping in hot water (HT) at 60 °C for 20 s. The effect of heat treatment on some cell wall genes involved in ripening such as β-galactosidase (β-GAL), pectin lyase (PL), polygalacturonase (PG) and pectin methyl esterase (PME), was analyzed by qRT-PCR. The expression levels of defense related genes, phenylalanine ammonia lyase (PAL) and chitinase (CHI), heat stress-related genes such as heat shock proteins 70 and 90 (HSP70, HSP90), and reactive oxygen species (ROS) scavenging genes were also evaluated by qRT-PCR. A 100% disease incidence reduction, as compared to untreated fruit, was obtained by treating 6 and 12 h after inoculation. Moreover, brown rot was inhibited by 85.7% when fruit were heat-treated 48 h after inoculation. The expression levels of cell wall genes (β-GAL, PL, PG and PME) showed a general decrease in HT fruit as compared to the control, whereas PAL, CHI, HSP70 and ROS-scavenging genes increased their expression level in HT samples with respect to the untreated ones. Our results show a curative activity of heat on peach inoculated with M. laxa 48 h before treatment. Each analyzed gene proved to be differentially expressed following heat treatment.     

Expression of ROP/RAC GTPase genes in postharvest loquat fruit in association with senescence and cold regulated lignification

ROP/RAC GTPases regulate various development processes and play important roles in plant defense responses. Recently, lignification or secondary cell wall formation related ROP members were reported in rice, zinnia, cotton and Eucalyptus. The present study aimed to investigate the possible association of loquat ROPs with flesh lignification under different temperatures. Four ROP cDNA fragments, EjROP1.1, EjROP1.2, EjROP2 and EjROP3, were isolated from ‘Luoyangqing’ (LYQ) loquat fruit, and all of them shared over 80% nucleotide identity with known ROPs from other plants. Sequence analysis revealed that EjROP1.1, EjROP2 and EjROP3 might be functional while EjROP1.2, with mutated C-terminal resulted from a 65 bp deletion in the corresponding nucleotide sequence as compared with EjROP1.1, might be dominant-negative and consequently act as a negative regulator of ROP signal transduction. Increase in expression of EjROP1.1, EjROP2 and EjROP3 was observed during first 4 or 6 d of storage at 20 °C and was positively correlated with the increase in flesh firmness. Expression of EjROP1.2 was constantly low under 20 °C but was quickly, within 6 h, induced under 0 °C, and it increased by about 20 times within 24 h. The expression was induced under 5 °C as well but not so strong as that under 0 °C, and transfer of fruit from 5 °C to 0 °C re-stimulated the expression. The possible roles of EjROPs played during senescence and cold regulated lignification was discussed, and the simultaneous increase in the expression of three functional EjROPs and the negative regulator EjROP1.2 was suggested to be important for maintaining a ROP rheostat to protect cells from excessive lignification. To our knowledge, this is the first study on a dominant-negative ROP resulted from a deletion mutation, and a ROP responded to low temperature.     

Diallel analysis of yield components of snap beans exposed to two temperature stress environments

Ten snap beans (Barrier, Brio, Carson, Cornell 502, CT 70, HB 1880, Hystyle, Labrador, Opus and Venture) were selected for differential temperature tolerance and used as parents in a complete diallel mating design. The 45 F₁ hybrid lines (with reciprocals) and parents were screened at 32 C day/28 C night, and in a separate experiment, 16 C day/10 C night, during reproductive development in replicated controlled environments. Variation for yield under temperature treatments was observed among parents and hybrids, with certain hybrids exceeding parental performance. Significant (P 0.0001) general combining ability (GCA), and significant (P 0.05) specific combining ability (SCA) were observed for yield components including pod number, seed number, and seeds per pod. There was evidence that pod number and seeds per pod under temperature stress are under separate genetic control. Reciprocal effects and heterosis were not significant. GCA could not be predicted from parental performance. The breeding line Cornell 502 had the highest GCA under high temperature, and the cultivar Brio had the highest GCA under low temperature. The cross Brio × Venture was high yielding in both temperature treatments. Heat tolerance and chilling tolerance were associated in certain parents and hybrids. However, performance under high and low temperature treatments was not generally correlated in the parents and hybrids, indicating that these traits should be selected separately.     

Climacteric and non-climacteric behavior in melon fruit: 2. Linking climacteric pattern and main postharvest disorders and decay in a set of near-isogenic lines

A set of near-isogenic lines (NILs) of melon (Cucumis melo L.) was used to test the relationship between the climacteric pattern and postharvest disorders at harvest and after 30 days at 8 °C. The NILs contained different chromosome introgressions in the linkage group III from the non-climacteric exotic Korean accession PI 161375 transferred into the genetic background of the non-climacteric Spanish cultivar ‘Piel de Sapo’ (PS). A quantitative trait locus (QTL) in this linkage group induced climacteric behavior in eight NILs accompanied by a peak of ethylene production and fruit dehiscence to different degrees. The cultivar ‘Nicolás’ and one NIL showed a non-climacteric pattern of respiration rate and ethylene production. The climacteric NILs were used to test the relationship between this pattern and postharvest disorders. The reference climacteric lines ‘Fado’ and ‘Védrantais’ were more sensitive to CI and associated Cladosporium rot than the NILs or PS. In general, a more intense climacteric behavior was accompanied by fruit dehiscence, and higher total losses and greater skin scald after storage, than in PS. A higher incidence of chilling injury (CI) in the climacteric NILs was found compared with the non-climacteric ones, although with exceptions (one NIL for CI in the form of scald; the same NIL and one more for pitting). The climacteric onset and netting scald were not related, and CI in the form of skin spots was only found in climacteric NILs and was positively correlated with the maximum peak of ethylene production. Some climacteric NILs did not follow the rule of a higher susceptibility to other disorders and decay after storage compared with PS, such as for example in fruit over-ripening (detected externally or internally), Cladosporium rot at the peduncle and Alternaria rot. Mealiness was independent of climacteric behavior. Three climacteric NILs obtained better flavor scores after storage than PS, although the maximum peak of ethylene production was positively correlated with off-flavor. Genotypic correlation between disorder data and the physiological data of climacteric fruit revealed positive (flavor index) or negative postharvest consequences (skin injuries, rots or off-flavors). At least one QTL can be assigned to most of the quality traits analyzed.