Chilling Stress Research Articles

Zinc Oxide Nanoparticles Alleviate Chilling Stress in Rice (Oryza Sativa L.) by Regulating Antioxidative System and Chilling Response Transcription Factors.

As one of the common abiotic stresses, chilling stress has negative effects on rice growth and development. Minimization of these adverse effects through various ways is vital for the productivity of rice. Nanoparticles (NPs) serve as one of the effective alleviation methods against abiotic stresses. In our research, zinc oxide (ZnO) NPs were utilized as foliar sprays on rice leaves to explore the mechanism underlying the effect of NPs against the negative impact of chilling stress on rice seedlings. We revealed that foliar application of ZnO NPs significantly alleviated chilling stress in hydroponically grown rice seedlings, including improved plant height, root length, and dry biomass. Besides, ZnO NPs also restored chlorophyll accumulation and significantly ameliorated chilling-induced oxidative stress with reduced levels of H2O2, MDA, proline, and increased activities of major antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). We further found that foliar application of ZnO NPs induced the chilling-induced gene expression of the antioxidative system (OsCu/ZnSOD1, OsCu/ZnSOD2, OsCu/ZnSOD3, OsPRX11, OsPRX65, OsPRX89, OsCATA, and OsCATB) and chilling response transcription factors (OsbZIP52, OsMYB4, OsMYB30, OsNAC5, OsWRKY76, and OsWRKY94) in leaves of chilling-treated seedlings. Taken together, our results suggest that foliar application of ZnO NPs could alleviate chilling stress in rice via the mediation of the antioxidative system and chilling response transcription factors.

Quantitative proteomics analysis reveals the response mechanism of peanut (Arachis hypogaea L.) to imbibitional chilling stress.

Imbibitional chilling stress inhibits normal seed germination and seedling establishment and leads to large losses in peanut production. This is a major limiting factor when sowing peanut earlier and further north. To reveal the response mechanism of peanut to imbibitional chilling stress, a Tandem Mass Tag (TMT)-based quantitative proteomics analysis was conducted to identify differentially accumulated proteins (DAPs) under imbibitional chilling stress. Hormone profiling and transcriptional analysis were performed to confirm the proteomics data. Further seed priming analysis with exogenous cytokinins was conducted to validate the role of cytokinins in alleviating imbibitional chilling injury. A total of 5029 proteins were identified and quantified in all of the experimental groups. Among these, 104 proteins were DAPs as compared with the control. Enrichment analysis revealed that these DAPs were significant in various molecular functional and biological processes, especially for biosynthesis and metabolism of plant hormones. Hormone profiling and transcription analysis suggested that the reduced abundance of cytokinin oxidase may be caused by down-regulation of gene expression of the corresponding genes and leads to an elevated content of cytokinins under chilling stress. Seed priming analysis suggested that exogenous application of cytokinins may alleviate injury caused by imbibitional chilling. Our study provides a comprehensive proteomics analysis of peanut under imbibitional chilling stress, suggesting the role of plant hormones in the response mechanism. The results provide a better understanding of the imbibitional chilling stress response mechanism in peanut that will aid in peanut production.

The Short-Term Metabolic Modulation of Basil (Ocimum basilicum L. cv. 'Genovese') after Exposure to Cold or Heat.

Chilling stress in spring and mid-season heat stress are important environmental stresses that can significantly affect plant productivity. The objectives of this study were to understand the effects of cold (4 and 10 °C) or heat (30 and 40 °C) stress on biochemical and physiological traits in leaves and roots of basil (Ocimum basilicum L. cv. ‘Genovese’) young plants. After short-time exposure to mild and severe temperature stresses, both photosynthetic pigments’ and protein, as well as enzymatic and non-enzymatic defense components in basil leaves and roots, were quantified and compared with the control non-stressed plants. It was shown that both cold and heat treatment increase the content of chlorophyll a, chlorophyll b, and carotenoids. Chilling correlated with higher content of soluble proteins in leaves, whereas the concentration of these osmoprotectants in roots was higher under both cold and heat stress. For all tested antioxidant enzymes, higher activity was measured in leaves, and activity was related to temperature stress. SOD, CAT, A-POX, and P-POX activities was induced under heat stress, while the higher activity of SOD, CAT, P-POX, and G-POX was recorded under cold stress, compared to the control. In addition to the induced activity of enzymatic components, the content of secondary metabolites including total phenolics, flavonoids, and total anthocyanins, was several times higher compared to the non-stressed plants. Furthermore, total phenolic content was higher in roots than in leaves. Significant positive correlation can be seen among photosynthetic pigments, SOD, total phenolics, and flavonoids under severe temperature stress (4 or 40 °C) in basil leaves, while for roots, positive correlation was found in the content of secondary metabolites and activity of CAT or peroxidases. Obtained results are discussed in terms of phenotyping of O. basilicum cv. ‘Genovese’ response to heat and chilling stress, which should contribute to a better understanding of merged responses to cold and heat tolerance of this valuable crop.

Effects of the interaction between vapor-pressure deficit and potassium on the photosynthesis system of tomato seedlings under low temperature

Both vapour pressure deficit (VPD) and potassium (K) have been widely studied in regulating leaf photosynthesis and plant growth. A close correlation between VPD and plant nutrient absorption has also been observed for diverse plant species under various environmental conditions. However, the interactive effect of VPD and K on plant photosynthesis remains unclear, especially at low temperatures. Here, we investigated the role of VPD in plant K uptake and the effects of VPD × K on plant photosynthesis system under chilling stress. Plants were subjected to different levels of K nutrient solution supply (2, 4, 8 mmol/L) with contrasting VPD levels (high vs. low). Compared to high VPD, low VPD increased plant transpiration, but there was no significant difference in leaf K content between different VPD treatments; K accumulation under low VPD increased significantly, which can be partly attributed to enhanced biomass production. Meanwhile, an increase in stomatal density and size occurred under low VPD conditions. Stomatal conductance and mesophyll conductance tended to increase with K level under low VPD condition, which was beneficial to the diffusion of carbon dioxide and thus increased photosynthesis. In terms of photosynthetic performance, low VPD and elevated K increased the utilization of light energy and reduced heat dissipation, which specifically manifested as up-regulated photosynthetic pigment content and chlorophyll fluorescence parameters and down-regulated Car/Chl ratio, NPQ, and ROS content. In summary, reducing VPD and adding K promoted photosynthetic performance and can alleviate the low-temperature stress of tomato plants.

Alleviating damage of photosystem and oxidative stress from chilling stress with exogenous zeaxanthin in pepper (Capsicum annuum L.) seedlings

As a typical thermophilous vegetable, the growth and yield of peppers are easily limited by chilling conditions. Zeaxanthin, a crucial carotenoid, positively regulates plant abiotic stress responses. Therefore, this study investigated the regulatory mechanisms of zeaxanthin-induced chilling tolerance in peppers. The results indicated that the pretreatment with zeaxanthin effectively alleviated chilling damage in pepper leaves and increased the plant fresh weight and photosynthetic pigment content under chilling stress. Additionally, alterations in photosynthetic chlorophyll fluorescence parameters and chlorophyll fluorescence induction curves after zeaxanthin treatment highlighted the participation of zeaxanthin in improving the photosystem response to chilling stress by heightening the quenching of excess excitation energy and protection of the photosynthetic electron transport system. In chill-stressed plants, zeaxanthin treatment also enhanced antioxidant enzyme activity and transcript expression, and reduced hydrogen peroxide (H2O2) and superoxide anion (O2•-) content, resulting in a decrease in biological membrane damage. Additionally, exogenous zeaxanthin upregulated the expression levels of key genes encoding β-carotene hydroxylase (CaCA1, CaCA2), zeaxanthin epoxidase (CaZEP) and violaxanthin de-epoxidase (CaVDE), and promoted the synthesis of endogenous zeaxanthin during chilling stress. Collectively, exogenous zeaxanthin pretreatment enhances plant tolerance to chilling by improving the photosystem process, increasing oxidation resistance, and inducing alterations in endogenous zeaxanthin metabolism.

Surveying Maize Seedlings as The First Step for Re-Evaluating Cold Tolerance in Maize Inbred Lines

The consequences of the current climate changes sustain the strategy of early sowing (early spring) to avoid drought during the flowering period and thus secure maize yields. Earlier sowing dates increase the risk of exposure of the plants to cold during the early development stages and thus re-evaluation of elite material is required to select more tolerant genotypes. The first step of re-evaluation is to define characteristics that could be used for fast survey of the elite material, before performing more profound analyses. The aim of this paper was to analyse morphological characteristics (radicle length, coleoptile length, seedling weight) of 5 day old seedlings of two inbred lines LK and Mo17 (according to breeders experience tolerant and susceptible, respectively) subjected to chilling stress (10°C day/8°C night) for 24h and 48h, as well as to perform morphological (root and shoot characteristics) and physiological (chlorophyl, flavonoid and anthocyanin contents) analyses of the plants after seven day recovery. Control plants were grown under optimal conditions (30°C day /20°C night, ≈60% humidity), at an 8h photoperiod. The results were not straightforward, as the susceptible Mo17 showed faster recovery (statistically insignificant differences between control and treatment plants for most of the analysed traits), while the tolerant LK was a more robust genotype throughout the experiment. Chlorophyl, flavonoid and anthocyanin contents were not informative. The results identified survival rate and root characteristics as informative for fast screening of seedlings for determination of cold tolerance.

OsGRF6 interacts with SLR1 to regulate OsGA2ox1 expression for coordinating chilling tolerance and growth in rice

Low temperature is one of the abiotic stressors that affect growth and productivity of rice. The plant hormone gibberellin not only regulates growth and development but is also involved in stress defense. Our rice seedling experiments demonstrated that overexpression of SLR1, a gene that encodes the rice DELLA protein, enhanced chilling tolerance. In contrast, overexpression of the active GA synthesis gene OsGA20ox1 reduced chilling tolerance, indicating that weakening GA signaling promoted plant defense against cold stress. CoIP-MS and BiFC assays showed that SLR1 physically interacted with OsGRF6. After cold treatment and recovery, the survival rates of OsGRF6-overexpression lines and an osgrf6 mutant and its complementary lines indicated that OsGRF6 is a negative regulator of chilling tolerance in rice. The yeast one-hybrid, qRT-PCR, and transactivation assays showed that both SLR1 and OsGRF6 can bind to the promoter of the active GA catabolic gene OsGA2ox1, where SLR1 promoted and OsGRF6 suppressed OsGA2ox1 expression. At normal temperature, OsGRF6 was responsible for maintaining active GA levels by inhibiting OsGA2ox1. When rice seedlings were subjected to chilling stress, the repressive effect of OsGRF6 on OsGA2ox1 was released by cold-induced SLR1, which activated OsGA2ox1 expression to decrease the active GA levels, enhancing chilling tolerance. These results suggest that OsGRF6 is an important regulator in the balance between growth and chilling tolerance in rice.

Comparative transcriptomic analysis reveals the cold acclimation during chilling stress in sensitive and resistant passion fruit (Passiflora edulis) cultivars.

Chilling stress (CS) is an important limiting factor for the growth and development of passion fruit (Passiflora edulis) in winter in South China. However, little is known about how the passion fruit responds and adapts to CS. In this study, we performed transcriptome sequencing of cold-susceptible cultivar Huangjinguo (HJG) and cold-tolerant cultivar Tainong 1 (TN1) under normal temperature (NT) and CS conditions, and a total of 47,353 unigenes were obtained by seven databases. Using differentially expressed unigenes (DEGs) analysis, 3,248 and 4,340 DEGs were identified at two stages, respectively. The Gene Ontology (GO) enrichment analysis showed that the DEGs were mainly related to phosphorylation, membrane protein, and catalytic activity. In Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, the unigenes of plant-pathogen interaction, plant hormone signal transduction and fatty acid metabolism were enriched. Then, the 12,471 filtered unigenes were clustered into eight co-expression modules, and two modules were correlated with CS. In this two modules, 32 hub unigenes were obtained. Furthermore, the unigenes related to CS were validated using quantitative real-time PCR (RT-qPCR). This work showed that the expression levels of CS-related unigenes were very different in two passion fruit cultivars. The results provide information for the development of passion fruit with increased chilling tolerance.

Functions of Oligosaccharides in Improving Tomato Seeding Growth and Chilling Resistance

Oligosaccharides help promote plant growth and resilience. In this study, chitosan oligosaccharide (CSOS), cello-oligosaccharide (COS), xylooligosaccharide (XOS), and oligomix (MixOS) (a mix of the three oligosaccharides (mass ratio 1:1:1)) were used to explore their possible regulatory abilities and mechanisms on tomatoes in normal conditions and chilling stress. In normal growth, the XOS had the greatest effect on increasing biomass (increased by 69.5%) in roots, and there was a significant increase (26.5%) of auxin (IAA) absorption. The COS increased main root length by 29.4%, but the content of methyl jasmonate (JA-ME) was 17% lower than other treatments. The MixOS was 2.7 times more effective in enhancing shoot biomass, and increased accumulation of IAA content by 30% above-ground. Under chilling stress, the plant photosynthetic activities and metabolic functions were less damaged with oligosaccharide treatments. In comparison to the control, COS, XOS, and CSOS effectively increased the content of soluble sugar and decreased the permeability of cell membrane, especially in the CSOS treatment in which soluble sugar increased by 37.8% and the permeability of cell membrane decreased by 35.4%. Similarly, the MixOS also possessed an effective resistance to chilling. These results suggested different oligosaccharides played different roles in plant growth, phenotype and resistance. The oligomix was the most effective in improving the plant growth and chilling tolerance. These novel results provide fundamental evidences for the development and application of oligosaccharide in sustainable agriculture.

Exogenous putrescine activates the arginine-polyamine pathway and inhibits the decomposition of endogenous polyamine in Anthurium andraeanum under chilling stress

Chilling temperature is an important abiotic stress that affects the product quality of Anthurium andraeanum. Exogenous putrescine (Put) can reduce the physiological damage caused by chilling stress on anthurium seedlings, and induce the synthesis of endogenous arginine (Arg). In this study, anthurium seedlings were pretreated with Put, Put+D-arginine (D-Arg), Put+difluoromethylornithine (DFMO), and Put+D-Arg+DFMO solutions for four weeks. Subsequently, the seedlings were subjected to chilling stress at 6 ºC for three days, followed by a recovery at 25 ºC for one day. The contents of endogenous Arg and polyamines (PAs), as well as the activities of arginine decarboxylase (ADC), ornithine decarboxylase (ODC), diamine oxidase (DAO), and polyamine oxidase (PAO) in the roots and leaves of each treatment group were measured during the experiments. The results were further confirmed on the transcriptional level via transcriptome sequencing and qRT-PCR. We found that the supplementation of Put promoted the synthesis of endogenous Arg and its conversion to PAs, and reduced the decomposition rate of endogenous PAs under chilling stress. ADC was the main enzyme that promoted the synthesis of endogenous Put. The supplementation of D-Arg or/and DFMO inhibited the synthesis of endogenous Arg and its conversion to Put, and accelerated the decomposition rate of endogenous PAs. The qRT-PCR confirmed four DEGs related to ADC, amino-acid acetyltransferase NAGS1 and polyamine biosynthetic process identified from the sequencing results. In summary, the supplementation of Put activated the arginine-polyamine pathway in anthurium under chilling stress, increased the activity of ADC and the expression of related genes, and moderately inhibited the decomposition of endogenous PAs. The supplementation of D-Arg or/and DFMO exhibited the opposite effects, which confirmed the effects of Put.

Cryopreservation of Porcine Embryos: Recent Updates and Progress.

Cryopreservation of embryos is important for long-distance embryo transfer and conservation of genetic resources. Porcine research is important for animal husbandry and biomedical research. However, porcine embryos are difficult to cryopreserve because of their high cytoplasmic lipid content and sensitivity to chilling stress. Vitrification is more efficient than slow freezing, and vitrification is mostly used in embryo cryopreservation. So far, the vitrification process of porcine embryos has been continuously improved, resulting in improved survival rates of warmed embryos and farrowing rates after the transplant procedure. It is worth noting that automatic vitrification has made great progress, which is expected to promote the standardization and application of vitrification. In this article, the vitrification process of porcine embryos at the blastula stage and early development stages is reviewed in detail. In addition, the efficiency of different vitrification systems was compared. In addition, we summarize technology that can improve the survival rate of cryopreserved porcine embryos, such as delipidation methods (including physical delipidation and chemical delipidation) and medium improvements (including chemically defined media and adding antioxidants). Meanwhile, gene expression changes during cryopreservation are also elaborated.

Tomato calmodulin-like protein SlCML37 is a calcium (Ca2+) sensor that interacts with proteasome maturation factor SlUMP1 and plays a role in tomato fruit chilling stress tolerance

Calmodulin-like proteins (CMLs), as well as their targets, play significant roles in various key developmental and stress responses in the plant. In tomato (Solanum lycopersicum), there are at least 52 CML genes in its genome. However, most of their functions are not well known, especially in response to cold stress. Here, we investigated SlCML37 biochemical and structural characteristics, including a typical α-helical secondary structure and exposing its hydrophobic regions after binding to Ca2+. Then we certificated that SlCML37 protein could physically interact with SlUMP1 by using yeast two-hybrid, bimolecular florescence complementation (BiFC) and GST pull-down assays. Further analysis showed that SlCML37-transgenic tomato fruit conferred significantly improved tolerance to chilling stress. This study indicates a possible role of calmodulin-like protein-mediated proteasome assemble in the regulation of plant cold response.

Mitochondrial small heat shock protein and chilling tolerance in tomato fruit

Our previous report indicated that tomato (Solanum lycopersicum) fruit of two contrasting varieties in the chilling tolerance showed the opposite expression pattern of a mitochondrial small heat shock protein (M-sHSP23.8) gene after chilling stress. Thus, the fruit of the relatively tolerant variety Micro-Tom strongly accumulated M-sHSP23.8 transcripts while the susceptible var. Minitomato fruit did not. To test whether M-sHSP23.8 is involved in tomato fruit protection mechanisms against chilling stress, Minitomato fruit overexpressing M-sHSP23.8 (OE23.8) and knockdown Micro-Tom fruit with reduced levels of M-sHSP23.8 (amiR23.8) were developed. After chilling treatment, most of the amiR23.8 fruit failed to ripen normally, showed wilting and skin wrinkles, partial discoloration, and did not reach full red color. On the contrary, these chilling injury symptoms were significantly diminished in OE23.8 fruit, showing less visible deterioration after chilling. Fruit of OE23.8 and amiR23.8 showed opposite patterns of water loss, electrolyte leakage, and expression of the tomato catalase 1 gene compared to control fruit. Membrane lipidome profile evidenced that amiR23.8 fruit showed differential adjustment of extraplastidic and plastidic lipids and variations in the lipid remodeling compared to control fruit, suggesting alterations in the membrane integrity. The high sensitivity of Micro-Tom amiR23.8 fruit and the better performance of Minitomato OE23.8 fruit to chilling treatment indicate that sHSP23.8 may be crucial in the chilling stress tolerance in tomato fruit.

Comparative transcriptome analysis of leaves during early stages of chilling stress in two different chilling-tolerant brown-fiber cotton cultivars.

Chilling stress generates significant inhibition of normal growth and development of cotton plants and lead to severe reduction of fiber quality and yield. Currently, little is known for the molecular mechanism of brown-fiber cotton (BFC) to respond to chilling stress. Herein, RNA-sequencing (RNA-seq)-based comparative analysis of leaves under 4°C treatment in two different-tolerant BFC cultivars, chilling-sensitive (CS) XC20 and chilling-tolerant (CT) Z1612, was performed to investigate the response mechanism. A total of 72650 unigenes were identified with eight commonly used databases. Venn diagram analysis identified 1194 differentially expressed genes (DEGs) with significant up-regulation in all comparison groups. Furthermore, enrichment analyses of COG and KEGG, as well as qRT-PCR validation, indicated that 279 genes were discovered as up-regulated DEGs (UDEGs) with constant significant increased expression in CT cultivar Z1612 groups at the dimensions of both each comparison group and treatment time, locating in the enriched pathways of signal transduction, protein and carbohydrate metabolism, and cell component. Moreover, the comprehensive analyses of gene expression, physiological index and intracellular metabolite detections, and ascorbate antioxidative metabolism measurement validated the functional contributions of these identified candidate genes and pathways to chilling stress. Together, this study for the first time report the candidate key genes and metabolic pathways responding to chilling stress in BFC, and provide the effective reference for understanding the regulatory mechanism of low temperature adaptation in cotton.

The Effect of Chilling and High-Temperature Stresses on the Growth and Physiological Changes of Grafted Cucumber in Iranian Endemic Squash and Cucumbers

The Effect of Chilling and High-Temperature Stresses on the Growth and Physiological Changes of Grafted Cucumber in Iranian Endemic Squash and Cucumbers

Antioxidative response and photosynthetic regulatory mechanisms in common fig leaves after short‐term chilling stress

AbstractCommon fig (Ficus carica L.) is widely cultivated Mediterranean species. Such warm‐climate species are adapted to elevated temperatures and are susceptible to chilling stress (0–12°C). However, occasional short chilling periods are common during growing season in temperate areas that can affect functionality of the plant. The aim of this work was to investigate influence of short‐term chilling stress on antioxidative response and PSII photochemistry in developing leaves of two common fig varieties: Zamorčica and Green matalon. Leaves were detached from the trees, acclimated at room temperature in dark for 16 hr and then exposed to low temperature (10°C) at low irradiation (50 μmol m−2 s−1) for 4 hr. Dark adapted leaves were considered as the control. The damage to the membranes was determined as lipid peroxidation (thiobarbituric acid reactive substances) while the antioxidative response was evaluated by determining activities of the selected antioxidative enzymes. Photosynthetic performance was analysed by measuring in vivo chlorophyll a fluorescence (ChlF) increase. Relative accumulation of the main photosynthetic proteins (D1 and Rubisco LSU) was determined, as well. Due to efficient antioxidative activity, neither of investigated variety showed damage of the membrane lipids. Both varieties revealed functional antennae and its good connectivity to their reaction centres shown as negative L and K bands as well as stable D1 protein accumulation suggesting functional electron transport through photosystem II (PSII) and efficient primary photochemistry. Blocked electron flow further than QA resulted in limitation of the Photosystem I (PSI) functionality in both varieties. Due to differential relative accumulation of D1 and Rubisco LSU proteins upon the chilling stress, Zamorčica revealed greater decrease of the main photosynthetic parameters derived from in vivo ChlF induction (PItotal, PIABS and φP0) in comparison to Green matalon. In addition, increased specific energy fluxes through PSII in Zamorčica suggested its higher susceptibility to photoinhibition caused by chilling stress in comparison to Green matalon.

Circadian clock-coordinated response to chilling stress in rice

Chilling is a major abiotic stress affecting rice growth and development. Circadian clock is an endogenous timer enabling plants to cope with ever changing surroundings. However, little is known about coordination of circadian clock in rice chilling tolerance. In this study, we found that seedlings only subjected to nighttime-chilling stress exhibited chlorosis phenotype, with yellower leaves compared to those undergoing cold only at daytime. Chlorophyll content and photosynthesis efficiency in seedlings under nighttime-chilling stress were significantly lower than that under daytime-chilling stress. Transcriptome analysis distinguished the COLD-REGULATED (COR) genes between daytime and nighttime. COR genes responding differentially to daytime- and nighttime-chilling were non-randomly distributed among rice chromosomes, clustering mainly in 8 chromosome arms, Chr. 1L, 1S, 2L, 2S, 3L, 3S, 4L and 7L. Among them, key genes for chlorophyll metabolism and photosynthesis were repressed by chilling stress during Zeitgeber time (ZT) at night but promoted by stress during ZT time in day, which was confirmed by qRT-PCR. Our study revealed impacts of circadian clock on rice chilling response, implying that manipulation of circadian clock has great potential to determine the magnitude of chilling response, and would be helpful for breeding new rice varieties with chilling tolerance.

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.

Global Analysis of Gene Expression Profiles in Glutinous Rice 89-1 (Oryza sativa L.) Seedlings Exposed to Chilling Stress

Rice (Oryza sativa) is a tropical cereal crop that is severely affected by chilling stress at the seedling stage, although glutinous rice 89-1 (Gr89-1) in Chongqing, China, shows tolerance to low temperatures and overwintering ability. However, little research has been conducted on the mechanisms regulating chilling stress in Gr89-1. In this study, a comprehensive of transcriptional profiles of Gr89-1 seedlings at the three-leaf stage was conducted after a 4 °C treatment for 2, 6, 12, 24, or 48 h. Overall, 2993 differentially expressed genes were detected in Gr89-1 seedlings upon cold exposure. Gene Ontology testing and pathway analysis revealed differentially expressed genes involved in transcriptional regulation, carbohydrate metabolism, plant hormone signal, and cell wall composition. A total of 243 transcription factors were differentially expressed during the cold treatment; in particular, the AP2/EREBP, bHLH, NAC, WRKY, C2H2, and TIFY families were generally upregulated after cold treatment, whereas the mTERF and GNAT families were downregulated. Chilling stress changed the starch and sucrose metabolism, coupled with the accumulation of sucrose and trehalose level, and increases in jasmonic acid level in Gr89-1 seedlings. Furthermore, a number of the cell wall-related genes identified in the present study were also differentially expressed during the cold treatment. The genes and pathways identified in the current study increase our understanding of the mechanisms underlying cold resistance in rice seedlings.

Effects of 1-MCP on proline, polyamine, and nitric oxide metabolism in postharvest peach fruit under chilling stress

Peach (Prunus persica Batsch ‘Yuhualu’) fruit are sensitive to chilling injury (CI). Proline, polyamine (PA), and nitric oxide (NO) are important small regulators of various metabolic pathways under chilling stress that mitigate CI. Ethylene is known to promote senescence and CI, while 1-methylcyclopropene (1-MCP) is an antagonist that inhibits the effects of ethylene. However, how 1-MCP and ethylene affect proline, PA, and NO levels under chilling stress remains unclear. To address these questions, 1-MCP (1 µL · L−1) and ethylene (1 µL · L−1) treatments were applied to peach fruit. Fruit were stored at 4 °C for 28 d, then moved to 25 °C for 3 d immediately after cold storage. Peach fruit exhibited CI symptoms after 7 d of cold storage with enhanced electrolyte leakage and malondialdehyde contents. The 1-MCP treatment significantly (P < 0.05) restrained peach CI, and fruit did not exhibit CI symptoms until 14 d of cold storage. Proline and PAs in peach under chilling stress were mostly synthesized from glutamate and arginine, which were catalyzed by Δ1-pyrroline-5-carboxylate synthetase and arginine decarboxylase, respectively. 1-MCP-treated fruit exhibited higher proline and PA contents and enhanced chilling tolerance compared to the control, while ethylene-treated fruit had lower proline and PA contents and reduced chilling tolerance. Ethylene-treated fruit, which exhibited more severe CI symptoms compared to the control, had significantly (P < 0.05) lower NO contents and NO synthase activities. However, NO may not be a direct acting factor in 1-MCP-induced chilling tolerance, as 1-MCP-treated fruit had lower NO contents and NO synthase activities compared to the control. In conclusion, proline and PA clearly played direct and important roles in 1-MCP-induced peach chilling tolerance, while NO may not be actively involved.