Low Non-freezing Temperatures Research Articles

Low frequency of the wild-type freezing-tolerance LsCBF7 allele among lettuce population suggests a negative selection during domestication and breeding.

Sustainable winter production in lettuce requires freezing tolerant varieties. This study identified a wild-type allele of LsCBF7 that could contribute to freezing tolerance improvement in lettuce. Lettuce is one of the most consumed vegetables globally. While ideally grown in 13-21°C, its cultivation extends into winter in milder climates. However, occasional freezing temperatures can significantly reduce yields. Therefore, the development of freezing-tolerant lettuce varieties has become a long-term goal of lettuce breeding programs. Despite its significance, our understanding of freezing tolerance in lettuce remains limited. Plants have evolved a coping mechanism against freezing, known as cold acclimation, whereby they can increase freezing tolerance when pre-exposed to low nonfreezing temperatures. The CBF pathway is well-known for its central role in cold acclimation. Previously, we identified 14CBFgenes in lettuce and discovered that one of them, LsCBF7, had a loss-of-function mutation. In this study, we uncovered that accessions from colder regions carried the wild-type allele ofLsCBF7and this allele likely contributed to increased freezing tolerance, with 14% of the lettuce population carrying this allele. Interestingly, in wild lettuce (L. serriola) that is considered a progenitor of cultivated lettuce, this wild-type allele was much more common, with a frequency of 90%. This finding suggests that this wild-type allele may have undergone negative selection during the domestication or breeding of lettuce. Our data strongly indicate that this allele could be linked to early bolting, an undesirable trait in lettuce, which may have driven the negative selection. While this wild-type allele shows promise for improving freezing tolerance in lettuce, it is crucial to decouple it from the early bolting trait to fully harness its potential in lettuce breeding.

Challenges in sunflower breeding for cold tolerance

Introduction. Sunflower is grown as an oilseed crop worldwide. For sunflower production, it is vital to have cold-tolerant hybrids. An appropriate method to assess cold tolerance is a prerequisite for successful breeding of cold-tolerant sunflower.
 Purpose and Objectives. To evaluate cold tolerance of sunflower in the laboratory and its tolerance in the field, to identify promising combinations, to assess the capacity of a laboratory test to predict tolerance of sunflower in the field and to verify relationships of cold tolerance with ripeness group and yield.
 Materials and Methods. Sunflower was grown in compliance with standard farming techniques. In total, 192 F1 hybrids were obtained. The lines and hybrids were screened for ability to germinate at above-zero low temperature by laboratory test. The field tolerance at the initial stages of plant growth was determined with a 9-point scale. Relationships between the investigated parameters were analyzed by linear regression.
 Results and Discussion. The highest field tolerance at the initial stages of plant growth was recorded for Kh4713V, Skh777А and Skh808А lines. However, they only conferred tolerance to some of their hybrids. On the other hand, several hybrids were fairly tolerant in the field though the tolerance scores of their parental lines ranged 1 to 5 points. There was no relationship between the ‘emergence – anthesis’ period and cold tolerance. A great degree of uncertainty is associated with predicting field tolerance of sunflower from its cold tolerance assessed by laboratory test. This laboratory test cannot be used to predict field tolerance of either lines or hybrids. There was a strong positive correlation between the field tolerance and seed yield in the lines, but the correlation coefficient for the hybrids indicated no significant correlation between these parameters.
 Conclusions. At non-freezing low temperatures, the yield of the inbred sunflower lines was positively correlated with the field tolerance score at the early stages of plant growth and development. There was no significant difference in responses of early- and medium-ripening sunflower genotypes to cold exposure. Lakhanov’s cold germination test is not appropriate for evaluation of field tolerance in sunflower lines and hybrids.

Optimized differential thermal analysis sheds light on the effect of temperature on peach floral bud cold hardiness and transition from endo- to ecodormancy

The greatest threat to profitable peach production is cold damage to reproductive tissues. To better understand and mitigate cold damage in peach accurate and efficient assessment of floral bud cold hardiness (Hc) is critical. Differential thermal analysis (DTA) was optimized for efficient and precise detection of low-temperature exotherms (LTE) created by the freezing of supercooled intracellular water in peach floral primordia to determine Hc weekly during the dormant season. DTA-estimated lethal temperatures (LT) were validated against the standard oxidative browning method (OB) and in situ field damage following three freezing events. Chilling (0–7.2 °C) accumulation tracked throughout the dormant season to determine DTA-related changes across dormancy phase transitions. LTEs showed rapid acclimation of ‘Redhaven’ peach floral buds following the first frost of the dormant season (Tmin=−6.8 °C on November 18, 2016) and maintained similar Hc levels for 45 days through maximum Hc (LT50 =−23.9 °C recorded on January 9, 2017) and until the accumulation of 868 chilling hours was reached. Following this milestone, a significant 55% loss of LTEs upon the accumulation of the first growing degree day (Tbase=7 °C) was recoded on February 7, 2017. An LTE recovery approach, pre-exposing buds to a non-freezing low temperature (−2°C) for a period of 12 h, more than doubled the number of LTEs detected for another 27 days extending DTA use for LT prediction. The results presented herein confirm that the use of DTA is efficient and accurate to determine Hc in peach floral buds, and suggest that the LTE loss in early spring may be a signature response related to the shift from endo- into ecodormancy following two environmental temperature cues, chilling satisfaction and the first heat accumulation post chilling satisfaction.

Non-photochemical quenching in natural accessions of Arabidopsis thaliana during cold acclimation

Cold acclimation, initiated by non-freezing low temperatures and light, is a natural strategy for increasing plant survival even at sub-zero temperatures. However, it remains unclear how the non-photochemical quenching processes, which are crucial for excessive light energy dissipation, are modulated during cold acclimation. We compared the effects of two weeks of acclimation to sub-optimal temperatures, at 10 °C (AC10) and 4 °C (AC4), with non-acclimated (NAC) Arabidopsis thaliana natural accessions grown at 21 °C, on their growth (rosette area), biochemistry (chlorophylls and epidermal flavonols), and physiology (CO2 assimilation rate, and quantum yields of photochemical and non-photochemical quenching processes). AC10 reduced rosette area in all (six) accessions, while chlorophylls and CO2 assimilation rate (Asat) decreased only in three accessions and it had no effect on maximum quantum yield (Fv/Fm). However, AC4 significantly decreased rosette area, chlorophylls, and Fv/Fm, in all accessions. Both AC10 and AC4 treatments increased the accumulation of epidermal flavonols in all accessions. In AC4 accessions, we found an increase in additional non-regulatory NPQ, Φf,d, and a decrease in the fraction of excitation energy used by PSII photochemistry, ΦPSII. A similar irradiance resulted in a marginal difference in regulatory NPQ, Φnpq, among NAC and AC10 or AC4 plants; however, AC10 plants have more energy-dependent fastest NPQ, ΦqE, whereas AC4 predominates state transition quenching, ΦqT. These variations in dissipation of absorbed light energy, when combined with reduced chlorophylls and accumulated flavonols, help to reduce the risk of photoinhibition in plants during cold periods. These findings provide new insights into how suboptimal temperature acclimation affects the regulation of NPQ molecular mechanisms in Arabidopsis thaliana natural accessions.

Contemplation on wheat vernalization.

Vernalization is a period of low non-freezing temperatures, which provides the competence to flower. This mechanism ensures that plants sown before winter develop reproductive organs in more favourable conditions during spring. Such an evolutionary mechanism has evolved in both monocot and eudicot plants. Studies in monocots, represented by temperate cereals like wheat and barley, have identified and proposed the VERNALIZATION1 (VRN1) gene as a key player in the vernalization response. VRN1 belongs to MADS-box transcription factors and is expressed in the leaves and the apical meristem, where it subsequently promotes flowering. Despite substantial research advancement in the last two decades, there are still gaps in our understanding of the vernalization mechanism. Here we summarise the present knowledge of wheat vernalization. We discuss VRN1 allelic variation, review vernalization models, talk VRN1 copy number variation and devernalization phenomenon. Finally, we suggest possible future directions of the vernalization research in wheat.

Temperature is an important driver for cold acclimation in garden roses

Low non-freezing temperatures and short days are two main environmental factors that can independently or collectively initiate cold acclimation in temperate perennials. Freezing temperatures are required for the full development of mid-winter cold hardiness. In the present study, six rose genotypes with different cold hardiness levels were selected to investigate cold acclimation under both long and short photoperiods to reveal the role of temperature and day length on cold acclimation of roses. A five-week short-day treatment at 20/18 °C did not induce cold acclimation in any of the genotypes. Cold hardiness levels (LT50 values) increased significantly at low non-freezing temperatures (2 °C) and freezing temperatures (-5 °C) irrespective of the photoperiod for all genotypes. The more cold-hardy ‘Dagmar Hastrup’ and ‘John Cabot’ responded strongly, achieving lower LT50 values under low non-freezing temperatures. Low non-freezing temperatures/freezing temperatures but not short days promoted the degradation of starch and the accumulation in sucrose, hexoses, and raffinose. Short days alone induced RhDHN5 in ‘Yesterday’, ‘Abraham Darby’, and Rosa wichurana. However, the expression of RhDHN5 was up-regulated significantly by low non-freezing temperatures in all genotypes. The up-regulation of RhBAM3 by lowering the temperature (low non-freezing temperatures and/or freezing temperatures) is genotype-independent. Freezing temperatures had a prominent role in accelerating the expression of RhGolS2 in all genotypes. The up-regulation of RhRS2 and RhRS6 is mainly induced by low non-freezing temperatures and freezing temperatures, respectively, but transcript levels for both were less pronounced than those for RhGolS2. Stem dehydration during cold acclimation was only found for ‘Chandos Beauty’ under long days and R. wichurana under short day length. R. wichurana was insufficiently acclimated to withstand freezing temperatures under short day length. This study clearly shows that the main factors triggering cold acclimation in roses in 5 rose genotypes are low non-freezing temperatures or freezing temperatures, but a synergistic effect of short photoperiod and low non-freezing temperatures was found for R. wichurana.

Nonfreezing Low Temperature Maintains the Viability of Menstrual Blood–Derived Endometrial Stem Cells Under Oxygen–Glucose Deprivation Through the Sustained Release of Autophagy-Produced Energy

Between the completion of the mesenchymal stem cell (MSCs) preparation and the transplantation into the patient, there is a time interval during which the quality control and transport of MSC products occur, which usually involves suspending the cells in normal saline in an oxygen–glucose deprivation (OGD) microenvironments. Thus, how to effectively maintain MSC viability during the abovementioned time interval is bound to play a significant role in the therapeutic effect of MSC-based therapies. Recently, menstrual blood–derived endometrial stem cells (MenSCs) have attracted extensive attention in regenerative medicine due to their superior biological characteristics, including noninvasive protocols for their collection, abundant source material, stable donation, and autotransplantation. Therefore, this study aimed to mainly determine the effect of storage temperature on the maintenance of MenSC viabilities in an OGD microenvironment, and to preliminarily explore its potential mechanism. Simultaneously, the effects of solvents commonly used in the clinic on MenSC viability were also examined to support the clinical application of MenSCs. Consequently, our results demonstrated that in the OGD microenvironment, a nonfreezing low temperature (4°C) was suitable and cost-effective for MenSC storage, and the maintenance of MenSC viability stored at 4°C was partly contributed by the sustained releases of autophagy-produced energy. Furthermore, the addition of human serum albumin effectively inhibited the cell sedimentations in the MenSC suspension. These results provide support and practical experience for the extensive application of MenSCs in the clinic.

HsfA1d promotes hypocotyl elongation under chilling via enhancing expression of ribosomal protein genes in Arabidopsis

How plants maintain growth under non-freezing low temperatures (chilling) is not well understood. Here we use hypocotyl elongation under dark to investigate molecular mechanisms for chilling growth in Arabidopsis thaliana. The function of HsfA1d (Heat shock transcription factor A1d) in chilling growth is investigated by physiological and molecular characterization of its mutants. Subcellular localization of HsfA1d under chilling is analyzed. Potential target genes of HsfA1d were identified by transcriptome analysis, chromatin immunoprecipitation, transcriptional activation assay, and mutant characterization. HsfA1d is a positive regulator of hypocotyl elongation under chilling. It promotes expression of a large number of ribosome biogenesis genes to a moderate but significant extent under chilling. HsfA1d could bind to the promoter regions of two ribosome protein genes tested and promote their expression. The loss of function of one ribosome gene also reduced hypocotyl elongation under chilling. In addition, HsfA1d did not have increased nuclear accumulation under chilling and its basal nuclear accumulation is promoted by a salicylic acid receptor under chilling. This study thus unveils a new HsfA1d-mediated pathway that promotes the expression of ribosomal protein genes which may maintain overall protein translation for plant growth in chilling.

The physiological response of the sweet cherry leaf to non-freezing low temperatures

The effect of exposure of sweet cherry trees (Prunus avium L.) to non-freezing low temperature was investigated by measurements of chlorophyll fluorescence, gas exchange parameters and chlorophyll content in two experiments. In Experiment I, cultivars ‘Grace Star’ and ‘Schneiders’ were exposed to an average of 4.7 °C 21 and 27 days after full blooming (DAFB) and in Experiment II, cultivar ‘Grace Star’ to 2.2 °C 50 DAFB, for one, two or three consecutive nights. The aim of the present study was to evaluate the effect of low temperature exposure (LTE) on leaf physiology, recovery time and differences between cultivars in response to chilling stress. After the first, second and third LTE, a decrease in maximum and effective quantum yield of PS II (Fv/Fm and Fv′/Fm′), net photosynthesis (Pn), stomatal conductance (gs) and transpiration (E) was observed. Multiple LTE caused a greater physiological disturbance than single LTE. The recovery time after multiple LTE was prolonged. Trees with one and two LTE reached similar values to the controls within 24 and 48 h, respectively, while trees with three LTE did not reach within 48 h. The LTE in Experiment I showed no effect on Fv/Fm, while two LTE induced lower Pn, gs and E. After LTE, no differences between cultivars were found. The effect of chilling stress was more pronounced at lower temperatures and when the trees were chilled for several consecutive nights.

Cold Stress Activates the Expression of Genes of the Chloroplast Transcription Apparatus in Arabidopsis thaliana Plants.

The physiological and molecular responses of Arabidopsis thaliana plants to cold stress were studied. Exposure to a low non-freezing temperature (4°C, 5 days) caused a decrease in the physiological functions and activity of a number of photosynthetic genes and elevation in expression of the cold stress gene COR15a, the product of which protects chloroplasts. It was shown for the first time that in parallel to a general inhibition of physiological functions under hypothermia, an increase in the expression of most genes for the chloroplast transcription apparatus was observed. This is obviously one of the compensatory mechanisms of adaptation aimed to maintain cellular homeostasis and physiological functions under hypothermia.

The cold response regulator CBF1 promotes Arabidopsis hypocotyl growth at ambient temperatures.

Light and temperature are two core environmental factors that coordinately regulate plant growth and survival throughout their entire life cycle. However, the mechanisms integrating light and temperature signaling pathways in plants remain poorly understood. Here, we report that CBF1, an AP2/ERF-family transcription factor essential for plant cold acclimation, promotes hypocotyl growth under ambient temperatures in Arabidopsis. We show that CBF1 increases the protein abundance of PIF4 and PIF5, two phytochrome-interacting bHLH-family transcription factors that play pivotal roles in modulating plant growth and development, by directly binding to their promoters to induce their gene expression, and by inhibiting their interaction with phyB in the light. Moreover, our data demonstrate that CBF1 promotes PIF4/PIF5 protein accumulation and hypocotyl growth at both 22°C and 17°C, but not at 4°C, with a more prominent role at 17°C than at 22°C. Together, our study reveals that CBF1 integrates light and temperature control of hypocotyl growth by promoting PIF4 and PIF5 protein abundance in the light, thus providing insights into the integration mechanisms of light and temperature signaling pathways in plants.

Presence of a basic secretory protein in xylem sap and shoots of poplar in winter and its physicochemical activities against winter environmental conditions.

XSP25, previously shown to be the most abundant hydrophilic protein in xylem sap of Populus nigra in winter, belongs to a secretory protein family in which the arrangement of basic and acidic amino acids is conserved between dicotyledonous and monocotyledonous species. Its gene expression was observed at the same level in roots and shoots under long-day conditions, but highly induced under short-day conditions and at low temperatures in roots, especially in endodermis and xylem parenchyma in the root hair region of Populus trichocarpa, and its protein level was high in dormant buds, but not in roots or branches. Addition of recombinant PtXSP25 protein mitigated the denaturation of lactate dehydrogenase by drying, but showed only a slight effect on that caused by freeze-thaw cycling. Recombinant PtXSP25 protein also showed ice recrystallization inhibition activity to reduce the size of ice crystals, but had no antifreezing activity. We suggest that PtXSP25 protein produced in shoots and/or in roots under short-day conditions and at non-freezing low temperatures followed by translocation via xylem sap to shoot apoplast may protect the integrity of the plasma membrane and cell wall functions from freezing and drying damage in winter environmental conditions.

Nitric oxide deficiency decreases C-repeat binding factor-dependent and -independent induction of cold acclimation.

Plant tolerance to freezing temperatures is governed by endogenous components and environmental factors. Exposure to low non-freezing temperatures is a key factor in the induction of freezing tolerance in the process called cold acclimation. The role of nitric oxide (NO) in cold acclimation was explored in Arabidopsis using triple nia1nia2noa1-2 mutants that are impaired in the nitrate-dependent and nitrate-independent pathways of NO production, and are thus NO deficient. Here, we demonstrate that cold-induced NO accumulation is required to promote the full cold acclimation response through C-repeat Binding Factor (CBF)-dependent gene expression, as well as the CBF-independent expression of other cold-responsive genes such as Oxidation-Related Zinc Finger 2 (ZF/OZF2). NO deficiency also altered abscisic acid perception and signaling and the cold-induced production of anthocyanins, which are additional factors involved in cold acclimation.

CBF-dependent and CBF-independent regulatory pathways contribute to the differences in freezing tolerance and cold-regulated gene expression of two Arabidopsis ecotypes locally adapted to sites in Sweden and Italy.

Arabidopsis thaliana (Arabidopsis) increases in freezing tolerance in response to low nonfreezing temperatures, a phenomenon known as cold acclimation. The CBF regulatory pathway, which contributes to cold acclimation, includes three genes—CBF1, CBF2 and CBF3—encoding closely-related transcription factors that regulate the expression of more than 100 genes—the CBF regulon—that impart freezing tolerance. Here we compare the CBF pathways of two Arabidopsis ecotypes collected from sites in Sweden (SW) and Italy (IT). Previous studies showed that the SW ecotype was more freezing tolerant than the IT ecotype and that the IT ecotype had a nonfunctional CBF2 gene. Here we present results establishing that the difference in CBF2 alleles contributes to the difference in freezing tolerance between the two ecotypes. However, other differences in the CBF pathway as well as CBF-independent pathways contribute the large majority of the difference in freezing tolerance between the two ecotypes. The results also provided evidence that most cold-induced CBF regulon genes in both the SW and IT ecotypes are coregulated by CBF-independent pathways. Additional analysis comparing our results with those published by others examining the Col-0 accession resulted in the identification of 44 CBF regulon genes that were conserved among the three accessions suggesting that they likely have important functions in life at low temperature. The comparison further supported the conclusion that the CBF pathway can account for a large portion of the increase in freezing tolerance that occurs with cold acclimation in a given accession, but that CBF-independent pathways can also make a major contribution.

Response of Сucumber (Cucumis sativus L.) Plants to Prolonged Permanent and Short-Term Daily Exposures to Chilling Temperature

We investigated the response of chilling-sensitive plants of cucumber (Cucumis sativus L.) to prolonged permanent (6 days) (PLT) and short-term (3 h) daily exposures to low non-freezing temperatures (9 and 12°С) (DROP) lying on different sides of the critical value (10°С) corresponding to a phase transition of membrane lipids in chilling-sensitive plants from a liquid-crystalline to a solid gel structure. Effects and aftereffects of DROP treatments at temperatures of 9 and 12°С (DROP9 and DROP12, respectively) were identical. They caused a reduction in linear dimensions of plants (as compared with control plants) and enhanced chilling tolerance of leaves but did not influence photosynthetic activity and water relations. However, when exposure to these temperatures was permanent (PLT9 and PLT12), their effects on plants were different. PLT9 almost entirely suppressed plant growth and development, inactivated photosynthetic apparatus (PSA), increased relative electrolite leakage (REL), and boosted lipid peroxidation (LPO). PLT12 also considerably reduced plant height and leaf area and suppressed (but did not inactivate) PSA; it did not boost POL or increased REL. It is important that, after the termination of chilling, PLT9 plants (unlike PLT12 plants) could not quickly resume growth and restore photosynthetic activity. Thus, considerable differences in plant responses to various patterns of chilling (long permanent or short-term daily) are probably due to the fact that, in the case of DROP treatments, relatively short-term (3 h) chilling of plants is followed in the diurnal cycle by a prolonged period (21 h) of optimal temperature when possible deviations and/or disturbances of PSA are restored and toxic substances that could accumulate in the course of chilling metabolized and/or neutralized. Pronounced differences in plant response to permanent exposure to temperatures of 9 and 12°С probably depend on the fact that these temperatures lie on different sides of a critical value (10°С) below which chilling-sensitive plants suffer grave physiological disturbances due to cooling. In addition, we showed that different responses of plants to PLT and DROP treatments are not determined by a usual dose-effect relationship but depend in many respects on the pattern of temperature influence (prolonged or short-term, single or recurring). As a result, the number of DROP spans experienced by plants in the experiments proved to be more important than their duration (at least, within a time interval from 2 to 12 h).

Gene Regulatory Networks Mediating Cold Acclimation: The CBF Pathway.

Under low nonfreezing temperature conditions, plants from temperate climates undergo physiological and biochemical adjustments that increase their tolerance to freezing temperatures. This response, termed cold acclimation, is largely regulated by changes in gene expression. Molecular and genetic studies have identified a small family of transcription factors, called C-repeat binding factors (CBFs), as key regulators of the transcriptomic rearrangement that leads to cold acclimation. The function of these proteins is tightly controlled, and an inadequate supply of CBF activity may be detrimental to the plant. Accumulated evidence has revealed an extremely intricate network of positive and negative regulators of cold acclimation that coalesce at the level of CBF promoters constituting a central hub where multiple internal and external signals are integrated. Moreover, CBF expression is also controlled at posttranscriptional and posttranslational levels further refining CBF regulation. Recently, natural variation studies in Arabidopsis have demonstrated that mutations resulting in changes in CBF expression have an adaptive value for wild populations. Intriguingly, CBF genes are also present in plant species that do not cold acclimate, which suggest that they may also have additional functions. For instance, CBFs are required for some cold-related abiotic stress responses. In addition, their involvement in plant development deserves further study. Although more studies are necessary to fully harness CBF biotechnological potential, these transcription factors are meant to be key for a rational design of crops with enhanced tolerance to abiotic stress.

Freezing Tolerance of Plant Cells: From the Aspect of Plasma Membrane and Microdomain.

Freezing stress is accompanied by a state change from water to ice and has multiple facets causing dehydration; consequently, hyperosmotic and mechanical stresses coupled with unfavorable chilling stress act in a parallel way. Freezing tolerance varies widely among plant species, and, for example, most temperate plants can overcome deleterious effects caused by freezing temperatures in winter. Destabilization and dysfunction of the plasma membrane are tightly linked to freezing injury of plant cells. Plant freezing tolerance increases upon exposure to nonfreezing low temperatures (cold acclimation). Recent studies have unveiled pleiotropic responses of plasma membrane lipids and proteins to cold acclimation. In addition, advanced techniques have given new insights into plasma membrane structural non-homogeneity, namely, microdomains. This chapter describes physiological implications of plasma membrane responses enhancing freezing tolerance during cold acclimation, with a focus on microdomains.

RESPONSE OF WHEAT PLANTS TO THE COMBINED IMPACT OF LOW TEMPERATURE AND CADMIUM

The response of wheat plants ( Triticum aestivum L.) to a combined (consecutive) impact of low temperature (4 ° С) and cadmium sulphate (100 µM) was investigated. Pretreatment of the seedlings with cadmium for 1 day caused an increase in cold tolerance, which continued during the following exposure to the 4 ° С temperature, reaching a maximum after 1–2 days, but decreasing somewhat in the end of the experiment (7 d). At the same time cadmium did not prevent the accumulation of fresh and dry biomass of the shoots at subsequent exposure of the seedlings to 4 ° С temperature, although it negatively affected the total chlorophyll content in the leaves. Pretreatment of the seedlings by chilling during 1 day also caused an increase in their cold tolerance, which persisted for a few days at subsequent exposure to cadmium, but decreased significantly in 6–7 days. Moreover, the chilling pretreatment decreased the accumulation of fresh and dry biomass of wheat shoots as well as the total chlorophyll content in the leaves at the subsequent prolonged cadmium impact. It was concluded that the response of wheat plants to a prolonged impact (7 d) of a low non-freezing temperature or cadmium changed significantly if preceded even by a short-term (1 d) treatment with the other stress factor. In particular, exposure to cadmium before chilling partially ‘disrupted’ the programme of cold adaptation, wherefore the plants’ resistance did not reach the level typical for cold hardening at a temperature of 4 ° С, and cold pretreatment of the plants, in turn, aggravated the negative effects of cadmium on cold tolerance, biomass accumulation and the content of photosynthetic pigments in wheat leaves.

Water relations, short-chain oligosaccharides and rheological properties in lettuces subjected to limited water supply and low temperature stress

Abstract Reducing water consumption and increasing the quality of vegetables is a particularly high priority in agricultural production. Thus, we set out to analyze the effect of restricting the water supply on water relations, rheological properties, and the accumulation of solutes and protective fructooligosaccharides (FOS) and raffinose family compounds (RFOs) in lettuces grown under controlled greenhouse conditions. In addition, we analyzed whether water restriction can prevent senescence-related changes and overcome the stress imposed by subsequent exposure to low temperature. Lettuces var. Maravilla de Verano were grown under three different water supply regimes, well-watered (WW), moderate water deficit (MWD) and severe water deficit (SWD). Our results indicate that accumulated transpiration (AT) was higher in WW plants than in lettuces subjected to water deficit. The relative water content (RWC) was significantly influenced by a restricted water supply but not by additional low temperature stress. Water deficit caused a significant decrease in the amount of unfreezable water (Uw), determined calorimetrically, in association with a significant decrease in total water content (T W ). After the additional low temperature stress, there was no further drop in Tw, although a significant decrease in Uw was evident, mainly in SWD lettuces. A moderate water deficit enhanced nystose and kestopentaose accumulation. After imposing low temperature stress, MWD lettuces had a lower apparent viscosity, concomitant with an increase in firmness, fewer senescence-related changes and a sharp increase in raffinose. We conclude that moderate water limitation, improving the endogenous levels of FOS and reducing the cleavage of wall polysaccharides backbones, thus reducing viscosity and increasing firmness, could be useful to retain water inside cells, avoiding quality loss and increasing the capacity of the lettuce to resist low non-freezing temperatures.

Deep Super-SAGE transcriptomic analysis of cold acclimation in lentil (Lens culinaris Medik.)

BackgroundFrost is one of the main abiotic stresses limiting plant distribution and crop production. To cope with the stress, plants evolved adaptations known as cold acclimation or chilling tolerance to maximize frost tolerance. Cold acclimation is a progressive acquisition of freezing tolerance by plants subjected to low non-freezing temperatures which subsequently allows them to survive exposure to frost. Lentil is a cool season grain legume that is challenged by winter frost in some areas of its cultivation.ResultsTo better understand the genetic base of frost tolerance differential gene expression in response to cold acclimation was investigated. Recombinant inbred lines (RILs) from the cross Precoz x WA8649041 were first classified as cold tolerant or cold susceptible according to their response to temperatures between −3 to −15 °C. Then, RILs from both extremes of the response curve were cold acclimated and the leaf transcriptomes of two bulks each of eight frost tolerant and seven cold susceptible RILs were investigated by Deep Super-SAGE transcriptome profiling. Thus, four RNA bulks were analysed: the acclimated susceptible, the acclimated tolerant and the respective controls (non-acclimated susceptible and non-acclimated tolerant). Approximately 16.5 million 26 nucleotide long Super-SAGE tags were sequenced in the four sets (between ~3 and 5.4 millions). In total, 133,077 different unitags, each representing a particular transcript isoform, were identified in these four sets. Tags which showed a significantly different abundance in any of the bulks (fold change ≥4.0 and a significant p-value <0.001) were selected and used to identify the corresponding lentil gene sequence. Three hundred of such lentil sequences were identified. Most of their known homologs coded for glycine-rich, cold and drought-regulated proteins, dormancy-associated proteins, proline-rich proteins (PRPs) and other membrane proteins. These were generally but not exclusively over-expressed in the acclimated tolerant lines.ConclusionsThis set of candidate genes implicated in the response to frost in lentil represents an useful base for deeper and more detailed investigations into this important agronomic trait in future.