Chilling Stress Conditions Research Articles

Exogenous Silicon Application Improves Chilling Injury Tolerance and Photosynthetic Performance of Citrus

Low-temperature stress is an important limiting factor affecting citrus growth and fruit yields. Therefore, increasing citrus cold stress tolerance may enhance the growth, yield, and quality of citrus production in marginal areas. The objective of this study was to determine the efficacy of silicon (Si) fertilizer application on cold-tolerance enhancement in citrus. Two citrus cultivars (Delta and Nules) were subjected to Si fertilization (control, 1000 mg L−1) and cold-stress temperature treatments (control and 0 °C for 72 h) using a 2 × 2 × 2 factorial treatment structure with six replications. Leaf gas exchange and chlorophyll fluorescence parameters, such as net photosynthetic rate (A), stomatal conductance (gs), transpiration rate (Tr), internal CO2 concentration (Ci), intrinsic water-use efficiency (iWUE), minimal fluorescence (Fo), maximum fluorescence (Fm), maximum quantum efficiency of PSII primary photochemistry of dark-adapted leaves (Fv/Fm), maximum quantum efficiency of PSII primary photochemistry of dark-/light-adapted leaves (F’v/F’m), electron transport rate (ETR), non-photochemical quenching (NPQ), and the relative measure of electron transport to oxygen molecules (ETR/A), were measured. The application of Si drenching to trees that were subsequently exposed to cold stress reduced gs, Tr, and Ci but improved iWUE and Fo in both cultivars compared to the Si-untreated trees. In addition, specific adaptation mechanisms were found in the two citrus species; NPQ and ETR were improved in Si-treated Valencia trees, while A, Fm, and ETR/A were improved in Clementine trees under chilling stress conditions. The current research findings indicate the potential of Si application to enhance cold stress tolerance in citrus, which can provide a strategy for growing citrus in arid and semi-arid regions that may experience cold stress. Overall, after the application of silicon drenching, the cold-sensitive citrus Valencia cultivar became as cold-tolerant as the cold-tolerant Clementine cultivar.

2-hydroxymelatonin (2-OHM), a major melatonin metabolite, confers multiple stress tolerance in pepper at seed germination stage

Besides affecting or regulating several crucial processes in plants’ growth and development, melatonin is also highly effective at reducing the oxidative damage induced by various abiotic stressors and therefore it is regarded as a new master plant hormone. The interaction of melatonin with several oxygenated compounds results in the formation of various metabolites that also exhibit melatonin-like functions. Although 2-hydroxymelatonin (2-OHM) is one of the principal melatonin metabolites found in plants, its possible roles in plant life are yet to be fully revealed. This study investigated the impact of 2-OHM treatment on pepper seed germination and seedling growth under various abiotic stress conditions. Pepper seeds treated with 50 µM 2-OHM were subjected to germination and emergence tests under chilling, salt, and water stress conditions. The results demonstrated that 2-OHM treatment significantly enhanced seed germination and seedling emergence performance compared to untreated seeds under stress conditions. The 2-OHM-treatemant resulted in higher final seed germination (FGP) and seedling emergence percentage (FEP) and root length under chilling and water stress conditions. Exogenously applied 2-OHM also significantly shortened the seed germination and emergence periods under chilling conditions as indicated by higher mean germination (MGT) and emergence rates (MET). Additionally, the 2-OHM treatment improved root length, FEP and MET under salt stress. In general, the 2-OHM treatment effectively reduced malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels while increasing proline content and amplifying the activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX) under all stress conditions. In conclusion, the 2-OHM treatment significantly improved seed germination and seedling performance and enhanced stress resilience in pepper at germination stage. This study highlights the potential of 2-OHM as an effective natural compound to enhance crop productivity and alleviate the adverse effects of abiotic stressors in agricultural practices. Future experiments will also assist in elucidation of 2-OHM intervened stress mitigation procedure in pepper.

Nitric Oxide Confers Chilling Stress Tolerance by Regulating Carbohydrate Metabolism and the Antioxidant Defense System in Melon (Cucumis melo L.) Seedlings

The objective of the present study was to consider the regulatory role of exogenous nitric oxide (NO) supplementation in response to chilling stress impose alterations on different physiological parameters in melon seedlings. Melon seedlings were treated with sodium nitroprusside (SNP, an NO donor), hemoglobin (a NO scavenger), NG-nitro-L-arginine methyl ester (an NO synthase inhibitor), and tungstate (a nitrite reductase inhibitor) under chilling stress conditions. The results showed that exogenous SNP improves the growth of melon seedlings under chilling stress conditions and ameliorates the harmful effects of chilling stress by increasing the levels of chlorophyll and soluble solutes, elevating the activity of sucrose phosphate synthase by enhancing the expression level of CmSPS. Moreover, exogenous NO significantly enhances the expression of genes and activities of antioxidant enzymes under chilling stress, resulting in lower reactive oxygen species accumulation. However, the protective effects of SNP are reversed by both NO scavenging and inhibition. Collectively, our results reveal that NO has the ability to ameliorate the harmful effects of chilling stress on melon seedlings by regulating carbohydrate metabolism and the antioxidant defense system.

Physiological genetic variation in tomato fruit chilling tolerance during postharvest storage.

Storage at low temperatures is a common practice to prolong postharvest life of fruit and vegetables with a minimal negative impact on human/environmental health. Storage at low temperatures, however, can be restricted due to produce susceptibility to non-freezing chilling temperatures, when injuries such as physiological disorders and decays may result in unmarketable produce. We have investigated tomato fruit response to postharvest chilling stress in a recombinant inbred line (RIL) population developed from a cross between a chilling-sensitive cultivated tomato (Solanum lycopersicum L.) breeding line and a chilling-tolerant inbred accession of the tomato wild species S. pimpinellifolium L. Screening of the fruit of 148 RILs under cold storage (1.5°C) indicated presence of significant variations in chilling tolerance, manifested by varying degrees of fruit injury. Two extremely contrasting groups of RILs were identified, chilling-tolerant and chilling-sensitive RILs. The RILs in the two groups were further investigated under chilling stress conditions, and several physiological parameters, including weight loss, chlorophyll fluorescence parameters Fv/Fm, and Performance Index (PI), were determined to be efficient markers for identifying response to chilling stress in postharvest fruit. The Fv/Fm values reflected the physiological damages endured by the fruit after cold storage, and PI was a sensitive marker for early changes in photosystem II function. These two parameters were early indicators of chilling response before occurrence of visible chilling injuries. Antioxidant activities and ascorbic acid content were significantly higher in the chilling-tolerant than the chilling-sensitive lines. Further, the expression of C-repeat/DREB binding factors (CBFs) genes swiftly changed within 1-hr of fruit exposure to the chilling temperature, and the SlCBF1 transcript level was generally higher in the chilling-tolerant than chilling-sensitive lines after 2-hr exposure to the low temperature. This research demonstrates the presence of potential genetic variation in fruit chilling tolerance in the tomato RIL population. Further investigation of the RIL population is underway to better understand the genetic, physiological, and biochemical mechanisms involved in postharvest fruit chilling tolerance in tomato.

Exogenous Bio-Based 2,3-Butanediols Enhanced Abiotic Stress Tolerance of Tomato and Turfgrass under Drought or Chilling Stress.

Among abiotic stresses in plants, drought and chilling stresses reduce the supply of moisture to plant tissues, inhibit photosynthesis, and severely reduce plant growth and yield. Thus, the application of water stress-tolerant agents can be a useful strategy to maintain plant growth under abiotic stresses. This study assessed the effect of exogenous bio-based 2,3-butanediol (BDO) application on drought and chilling response in tomato and turfgrass, and expression levels of several plant signaling pathway-related gene transcripts. Bio-based 2,3-BDOs were formulated to levo-2,3-BDO 0.9% soluble concentrate (levo 0.9% SL) and meso-2,3-BDO 9% SL (meso 9% SL). Under drought and chilling stress conditions, the application of levo 0.9% SL in creeping bentgrass and meso 9% SL in tomato plants significantly reduced the deleterious effects of abiotic stresses. Interestingly, pretreatment with levo-2,3-BDO in creeping bentgrass and meso-2,3-BDO in tomato plants enhanced JA and SA signaling pathway-related gene transcript expression levels in different ways. In addition, all tomato plants treated with acibenzolar-S-methyl (as a positive control) withered completely under chilling stress, whereas 2,3-BDO-treated tomato plants exhibited excellent cold tolerance. According to our findings, bio-based 2,3-BDO isomers as sustainable water stress-tolerant agents, levo- and meso-2,3-BDOs, could enhance tolerance to drought and/or chilling stresses in various plants through somewhat different molecular activities without any side effects.

Melatonin Application Modifies Antioxidant Defense and Induces Endoreplication in Maize Seeds Exposed to Chilling Stress.

The aim of the study was to demonstrate the biostimulating effect of exogenous melatonin (MEL) applied to seeds via hydroconditioning. It was indicated that only well-chosen application technique and MEL dose guarantees success concerning seed germination and young seedlings growth under stress conditions. For maize seed, 50 μM of MEL appeared to be the optimal dose. It improved seed germination and embryonic axes growth especially during chilling stress (5 °C/14 days) and during regeneration after its subsided. Unfortunately, MEL overdosing lowered IAA level in dry seeds and could disrupt the ROS-dependent signal transduction pathways. Very effective antioxidant MEL action was confirmed by low level of protein oxidative damage and smaller quantity of lipid oxidation products in embryonic axes isolated from seeds pre-treated with MEL and then exposed to cold. The stimulatory effects of MEL on antioxidant enzymes: SOD, APX and GSH-PX and on GST-a detoxifying enzyme, was also demonstrated. It was indicated for the first time, that MEL induced defence strategies against stress at the cytological level, as appearing endoreplication in embryonic axes cells even in the seeds germinating under optimal conditions (preventive action), but very intensively in those germinating under chilling stress conditions (intervention action), and after stress removal, to improve regeneration.

Melatonin effects in enhancing chilling stress tolerance of pepper

Chilling stress is a type of low temperature stress that occurs when plants are exposed to temperatures below optimum but above 0 °C. It determines the geographical distribution of crop species that are of tropic and sub-tropic origin and causes huge losses every year. Thus, besides developing stress tolerant crop varieties, the use of various substances has become an important way of alleviating the adverse effects of abiotic stress conditions and melatonin has gained huge attention lately due to its proven anti-oxidative nature. The objective of the present study was to explore if exogenous application of melatonin through soil drench would mitigate the damage caused by chilling stress in pepper at seedling and flowering stages. Pepper seedlings and flowering plants were treated with melatonin after which they were subjected to chilling stress at 5 °C/10 °C (night/day) for 3 days. The results indicated that melatonin application resulted in reduced visual damage but increased leaf area and shoot mass in pepper seedlings. Melatonin treatment also improwed water relations, photosynthetic parameters and the activities of antioxidant enzymes while lowering malondialdehyde (MDA) and H2O2 contents and membrane permeability. When applied at flowering stage, melatonin doubled the early yield but caused slight increase in the final yield. Thus, the results of this research indicate that treatment of pepper plants with 5 µM melatonin through soil drench could be used to improve plant growth and early yield potential under chilling stress conditions.

Chitosan-Phenylalanine Nanoparticles (Cs-Phe Nps) Extend the Postharvest Life of Persimmon (Diospyros kaki) Fruits under Chilling Stress

There are high levels of damage imposed on persimmon fruit postharvest, especially after storing it in cold storage, which causes chilling injury (CI). To reduce this stress on the fruit, the conventional way is to use chemical treatments. Since there is a limitation in the use of chemical materials, it is necessary to apply non-harmful treatments to decrease chilling injury and maintain the quality of persimmon in cold storage. The aim of this study is to investigate the effects of chitosan-loaded phenylalanine nanoparticles (Cs-Phe NPs) (2.5 and 5 mM) on physiochemical and quality factors of persimmon (Diospyros kaki) during 45 days of storage at 4 °C (38 °F) and evaluate the impact of Cs-Phe NPs on the preserving quality in order to reduce the chilling injury of this fruit. The experiment was conducted using a completely randomized design with three replications. Treatments were applied at 15, 30, and 45 days after storage at 4 °C with ≥90% relative humidity. The size of Cs-Phe NPs was less than 100 nm, approximately. The results showed that application of 5 mM of Cs-Phe NPs delayed the negative effects of chilling stress and enhanced antioxidant capacity, firmness, and total soluble solids of persimmon fruit. Lower H2O2 and malonaldehyde (MDA) accumulation along with higher soluble tannin and total carotenoid accumulation in persimmon fruit treated with 5 mM Cs-Phe NPs was also observed. Fruit coated using Cs-Phe NPs in both concentrations (2.5 and 5 mM) showed the highest antioxidant enzyme activity for superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) and the lowest for polyphenol oxidase (PPO) and chilling injury during storage. According to our results, 5 mM of Cs-Phe NPs could be considered as the best treatment under chilling-stress conditions.

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.

Effects of 5-aminolevulinic acid on osmotic adjustment and antioxidant system in mung bean under chilling stress

Effects of 5-aminolevulinic acid on osmotic adjustment and antioxidant system in mung bean under chilling stress

A universal pipeline for mobile mRNA detection and insights into heterografting advantages under chilling stress

Heterografting has long been used to enhance the chilling tolerance of temperature-sensitive crops, including watermelon, whose mechanism is known to involve bidirectional long-distance mRNA movements. Despite several studies reporting on mobile mRNA (mb-mRNA) profiles in plants, accurate identification of mb-mRNAs is challenging owing to an array of technical problems. Here, we developed a bioinformatical pipeline that took most of the known technical concerns into consideration and is considered to be a universal tool for mb-mRNA detection in heterografts. By applying this pipeline to a commercial watermelon–bottle gourd heterografting system, we detected 130 and 1144 mb-mRNAs upwardly and 167 and 1051 mb-mRNAs downwardly transmitted under normal and chilling-stress conditions, respectively. Quantitative real-time PCR indicated a high accuracy rate (88.2%) of mb-mRNA prediction with our pipeline. We further revealed that the mobility of mRNAs was not associated with their abundance. Functional annotation and classification implied that scions may convey the stress signal to the rootstock, subsequently triggering energy metabolism reprogramming and abscisic acid-mediated stress responses by upward movement of effective mRNAs, ultimately leading to enhanced chilling tolerance. This study provides a universal tool for mb-mRNA detection in plant heterografting systems and novel insights into heterografting advantages under chilling stress.

L-Triptofan ve Melatonin’in Düşük ve Yüksek Sıcaklık Koşullarında Turp ve Ispanağın Tohum Çimlenme Performansına Etkileri

Bu çalışmanın amacı L-Triptofan ve Melatonin uygulamalarının farklı sıcaklık koşullarında turp ve ıspanak tohumlarının çimlenme özellikleri üzerindeki etkilerini araştırmaktır. Farklı konsantrasyonlarda L-Triptofan (125, 250, 375 ppm) ve Melatonin (5, 10, 25 µM) ile muamele edilmiş tohumlar, optimum (21 ˚C), üşüme stresi (7˚C) ve yüksek sıcaklık (35 ˚C) koşullarında çimlenme testlerine tabi tutulmuştur. Distile su ile muamele edilmiş tohumlar kontrol olarak kabul edilmiştir. Denenen hormonlar, düşük sıcaklıkta (7 ˚C) turp tohumlarının ortalama çimlenme süresi, %50 çimlenme oranına ulaşma süresi ve taze ağırlık sonuçları üzerine önemli etkiler oluşturmuştur. Bu sıcaklık derecesinde, 10 µM melatonin uygulaması, ortalama çimlenme süresini ve tohumların %50 çimlenme oranına ulaşma süresini, hormon uygulanmamış tohumlara göre uzatmıştır. 125 ppm ve 250 ppm L-Triptofan uygulaması yaş ağırlık değerlerini artırmıştır. Ispanak tohumlarında düşük sıcaklık koşulunda (7 ˚C) hormon uygulamalarının en büyük etkisi %50 çimlenmeye ulaşmak için gerekli süre özelliğinde gözlenmiştir. L-Triptofan' ın 375 ppm dozu bu süreyi kontrole göre kısaltırken, 25 µM melatonin uygulaması ise uzatmıştır.

Influence of L-Tryptophan and Melatonin on Germination of Onion and Leek Seeds at Different Temperatures

In this study, the effects of pre-sowing L-Tryptophan and Melatonin treatments on germination of onion and leek seeds under different temperature conditions were investigated. Seeds were treated with 125, 250, 375 ppm L-Tryptophan and 5, 10, 25 uM Melatonin for 24 hours, then subjected to germination tests at optimum (21 ˚C) chilling stress (7 ˚C) and hot temperature (35˚C) conditions. Treated with distilled water seeds were considered as controls. Treatment of onion seeds with 125 ppm L-tryptophan had a significantly positive effect on final germination ratio at 7˚C while in leek seeds, the 5 µM concentration of melatonin had a significant effect on the germination index at the same temperature. In both Allium species, hormone treatments had no effect on mean germination time. These values decreased depending on the increase in temperature. The extreme level of high temperature burned certain percent of seedlings, while at low temperature, seedlings were not harmed by cold domination.

The tomato 2-oxoglutarate-dependent dioxygenase gene SlF3HL is critical for chilling stress tolerance

Low temperature is a major stress that severely affects plant development, growth, distribution, and productivity. Here, we examined the function of a 2-oxoglutarate-dependent dioxygenase-encoding gene, SlF3HL, in chilling stress responses in tomato (Solanum lycopersicum cv. Alisa Craig [AC]). Knockdown (KD) of SlF3HL (through RNA interference) in tomato led to increased sensitivity to chilling stress as indicated by elevated levels of electrolyte leakage, malondialdehyde (MDA) and reactive oxygen species (ROS). In addition, the KD plants had decreased levels of proline and decreased activities of peroxisome and superoxide dismutase. The expression of four cold-responsive genes was substantially reduced in the KD plants. Furthermore, seedling growth was significantly greater in AC or SlF3HL-overexpression plants than in the KD plants under either normal growth conditions with methyl jasmonate (MeJA) or chilling stress conditions. SlF3HL appears to positively regulate JA accumulation and the expression of JA biosynthetic and signaling genes under chilling stress. Together, these results suggest that SlF3HL is a positive regulator of chilling stress tolerance and functions in the chilling stress tolerance pathways, possibly by regulating JA biosynthesis, JA signaling, and ROS levels.

Selenium Improves Physiological Parameters and Alleviates Oxidative Stress in Strawberry Seedlings under Low-Temperature Stress.

Here, we investigated the effects of selenium (Se) applications on two strawberry varieties, Akihime and Benihoppe, under chilling stress and recovery conditions. Changes in photosynthetic parameters, antioxidant enzyme activities, ascorbate (AsA)-glutathione (GSH) cycle-related enzyme activities, and low-molecular-mass antioxidant contents were determined. Foliar spraying with Se alleviated the decline in the net photosynthetic rate and chlorophyll content and increased the malondialdehyde and hydrogen peroxide contents of strawberry seedlings’ leaves under chilling stress. As the time under chilling stress increased, the stomatal conductance decreased and intercellular CO2 concentration increased, suggesting that nonstomatal factors had major limiting effects on the net photosynthetic rate’s decrease. Se applications significantly alleviated the adverse impacts of chilling stress on changes in stomatal conductance and intercellular CO2 concentration. Se, especially at lower concentrations, significantly increased superoxide dismutase, catalase, and peroxide enzyme activities during chilling stress. Approximately 5 mg·L−1 of sodium selenite solution had the greatest stress-alleviating effects. Among the AsA-GSH cycle-related enzymes, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase (MDHAR) treatments, coupled with an appropriate dose of Se, significantly enhanced ascorbate peroxidase and MDHAR activities, which suggested that Se applications played important roles in strawberry leaves by affecting AsA-GSH cycle-related defenses against the oxidative damage caused by chilling stress. Furthermore, MDHAR was the key enzyme required to maintain the balance between AsA consumption and regeneration that may assist in protecting strawberry seedlings in a low-temperature environment.

Low temperature induced oxidative stress tolerance in oats (Avena sativa L.) genotypes

Chilling tolerance adaptation in plant cell can be correlated with efficiency of antioxidant defence system, antioxidants and osmoprotectants. In this study, such responses were comparatively studied in four high yielding oats genotypes (OL-9, OL-10, OL-125, Kent) under control (25 °C) and chilling stress (5 °C) conditions. Cold temperature upregulated the activites of catalase, guaiacol peroxide, ascorbate peroxidase (APX), glutathione reductase in root and shoot of all four genotypes. The SOD enzyme activity was decreased in both organs by 32% with chilling stress. Chilling stress increased redox potential of plant cell significantly by increasing the level of ascorbate and glutathione in order to cope up the reactive oxygen species The concentration of proline, total phenol, total sugar, H2O2, soluble protein and free amino acids was increased with imposition of cold stress in both roots and shoots though a decline in MDA content was observed. The observed biochemical diversity revealed that catalase, APX, glutathione and sugars appeared to have greater role in conferring chilling tolerance in oats genotypes as indicated by their greater variations with cold stress.

High throughput deep sequencing reveals the important roles of microRNAs during sweetpotato storage at chilling temperature

Sweetpotato (Impomoea batatas L.) is a globally important economic food crop with a potential of becoming a bioenergy and pharmaceutical crop. Thus, studying the molecular mechanism of tuberous root development and storage is very important. However, not too much progress has been made in this field. In this study, we employed the next generation high-throughput deep sequencing technology to sequence all small RNAs and degradome of sweetpotato for systematically investigating sweetpotato response to chilling stress during storage. A total of 190 known microRNAs (miRNAs) and 191 novel miRNAs were identified, and 428 transcripts were targeted by 184 identified miRNAs. More importantly, we identified 26 miRNAs differentially expressed between chilling stress and control conditions. The expression of these miRNAs and their targets was also confirmed by qRT-PCR. Integrated analysis of small RNAs and degradome sequencing reveals that miRNA-mediated SA signaling, ABA-dependent, and ROS response pathways are involved in sweetpotato root response to chilling stress during storage.

The Effects of Seed Treatment with Melatonin on Germination and Emergence Performance of Pepper Seeds under Chilling Stress

Melatonin was first isolated from bovine pineal gland more than half a century ago as an important animal hormone and since then it was proved to be present in almost all forms of life including eukaryotic unicells, prokaryotes, fungi, algae, animals and plants. In this study, the effects of pre-sowing seed treatment with melatonin on germination and emergence performance of pepper seeds under chilling conditions were investigated. Seeds were immersed in 0, 1, 5, 10 or 25 µM melatonin solutions for 24 hours after which they were dried for one day and subjected to germination and emergence tests at optimum and chilling stress conditions. Exogenous melatonin treatment promoted pepper seed germination and emergence under chilling conditions. Treatment of seeds with melatonin especially in 1 or 5 µM concentrations significantly improved germination and emergence percentage and rate whereas dry seeds and seeds treated with 0 µM melatonin exhibited the lowest germination and emergence performance. Melatonin application also reduced the MDA and H 2 O 2 content and elevated SOD and CAT enzyme activity. The improvement in germination and emergence performance of pepper under chilling stress conditions following melatonin treatment may therefore be due to reduced lipid peroxidation and elevated activities of antioxidant enzymes.

Interaction of Polyamines, Abscisic Acid, Nitric Oxide, and Hydrogen Peroxide under Chilling Stress in Tomato (Lycopersicon esculentum Mill.) Seedlings.

Polyamines (PAs) play a vital role in the responses of higher plants to abiotic stresses. However, only a limited number of studies have examined the interplay between PAs and signal molecules. The aim of this study was to elucidate the cross-talk among PAs, abscisic acid (ABA), nitric oxide (NO), and hydrogen peroxide (H2O2) under chilling stress conditions using tomato seedlings [(Lycopersicon esculentum Mill.) cv. Moneymaker]. The study showed that during chilling stress (4°C; 0, 12, and 24 h), the application of spermidine (Spd) and spermine (Spm) elevated NO and H2O2 levels, enhanced nitrite reductase (NR), nitric oxide synthase (NOS)-like, and polyamine oxidase activities, and upregulated LeNR relative expression, but did not influence LeNOS1 expression. In contrast, putrescine (Put) treatment had no obvious impact. During the recovery period (25/15°C, 10 h), the above-mentioned parameters induced by the application of PAs were restored to their control levels. Seedlings pretreated with sodium nitroprusside (SNP, an NO donor) showed elevated Put and Spd levels throughout the treatment period, consistent with increased expression in leaves of genes encoding arginine decarboxylase (LeADC. LeADC1), ornithine decarboxylase (LeODC), and Spd synthase (LeSPDS) expressions in tomato leaves throughout the treatment period. Under chilling stress, the Put content increased first, followed by a rise in the Spd content. Exogenously applied SNP did not increase the expression of genes encoding S-adenosylmethionine decarboxylase (LeSAMDC) and Spm synthase (LeSPMS), consistent with the observation that Spm levels remained constant under chilling stress and during the recovery period. In contrast, exogenous Put significantly increased the ABA content and the 9-cis-epoxycarotenoid dioxygenase (LeNCED1) transcript level. Treatment with ABA could alleviate the electrolyte leakage (EL) induced by D-Arg (an inhibitor of Put). Taken together, it is concluded that, under chilling stress, Spd and Spm enhanced the production of NO in tomato seedlings through an H2O2-dependent mechanism, via the NR and NOS-like pathways. ABA is involved in Put-induced tolerance to chilling stress, and NO could increase the content of Put and Spd under chilling stress.

Impacts of chilling on photosynthesis and chlorophyll pigment content in juvenile basil cultivars

The objective of this study was to examine several cultivars of Ocimum basilicum L. (green, red, cinnamon, lettuce leaf, lemon, and Thai basils) for photosynthetic performance, chlorophyll a fluorescence, and chlorophyll content under chilling stress conditions of 6°C in comparison to non-stressed controls (18°C). The basil plants were grown in a peat substrate for 8 weeks and then exposed to chilling for 8 or 16 days, under a 300 μmol•m-2•s-1 photosynthetic photon flux. After chilling, significant reductions in both the transpiration (E) and net photosynthetic (PN) rates were observed in basil plants, while the intercellular CO2 concentration (Ci) was higher in the plants treated with 6°C in comparison to the controls. The decrease in PN and E was associated with decreased water use efficiency (WUE) and stomatal conductance (gs). The greatest impairment of photosynthesis for Thai basil leaves was observed after 8 days of chilling, and for green basil after the 16-day low temperature treatment. The photosystem II (PSII) activity (Fv/Fm) and variable-to-initial chlorophyll fluorescence (Fv/F0) were decreased after chilling. PSII activity was most affected in lettuce leaf basil after 8 days, and in Thai and red basil plants after the prolonged temperature treatment. Low temperatures did not significantly alter the chlorophyll concentration but did increase the Chl a/b ratio in leaves of basil. The results indicated that the decrease in photosynthesis was not attributable mainly to damage to PSII, but rather to chilling-induced photoinhibition of PSI. The knowledge gained in this study on the genotypic variation in basil response should be helpful for future selection of plants with low chilling sensitivity.