Chilling-sensitive Plants Research Articles

Chilling stress drives organ-specific transcriptional cascades and dampens diurnal oscillation in tomato.

Improving chilling tolerance in cold-sensitive crops, e.g. tomato, requires knowledge of the early molecular response to low temperature in these under-studied species. To elucidate early responding processes and regulators, we captured the transcriptional response at 30minutes and 3hours in the shoots and at 3hours in the roots of tomato post-chilling from 24°C to 4°C. We used a pre-treatment control and a concurrent ambient temperature control to reveal that majority of the differential expression between cold and ambient conditions is due to severely compressed oscillation of a large set of diurnally regulated genes in both the shoots and roots. This compression happens within 30minutes of chilling, lasts for the duration of cold treatment, and is relieved within 3hours of return to ambient temperatures. Our study also shows that the canonical ICE1/CAMTA-to-CBF cold response pathway is active in the shoots, but not in the roots. Chilling stress induces synthesis of known cryoprotectants (trehalose and polyamines), in a CBF-independent manner, and induction of multiple genes encoding proteins of photosystems I and II. This study provides nuanced insights into the organ-specific response in a chilling sensitive plant, as well as the genes influenced by an interaction of chilling response and the circadian clock.

The ability of P700 oxidation in photosystem I reflects chilling stress tolerance in cucumber.

Low temperature inhibits photosynthesis and negatively affects plant growth. Cucumber (Cucumis sativusL.) is a chilling-sensitive plant, and its greenhouse production requires considerable energy during the winter. Therefore, a useful stress marker for selecting chilling-tolerant cucumber cultivars is desirable. In this study, we evaluated chilling-stress damage in different cucumber cultivars by measuring photosynthetic parameters. The majority of cultivars showed decreases in the quantum yield of photosystem (PS) II [Fv/Fm and Y(II)] and the quantity of active PS I (Pm) after chilling stress. In contrast, Y(ND)-the ratio of the oxidized state of PSI reaction center chlorophyll P700 (P700+)-differed among cultivars and was perfectly inversely correlated with Y(NA)-the ratio of the non-photooxidizable P700. It has been known that P700+ accumulates under stress conditions and protects plants to suppress the generation of reactive oxygen species. In fact, cultivars unable to induce Y(ND) after chilling stress showed growth retardation with reductions in chlorophyll content and leaf area. Therefore, Y(ND) can be a useful marker to evaluate chilling-stress tolerance in cucumber.

Dehydration-Responsive Element Binding Protein 1C, 1E, and 1G Promote Stress Tolerance to Chilling, Heat, Drought, and Salt in Rice.

The dehydration-responsive element binding protein 1 (DREB1)/C-repeat-binding factor (CBF) genes are key regulators of cold acclimation and freezing tolerance in the chilling tolerant Arabidopsis thaliana. Here, we investigated the function of three members of the 10 rice DREB1 genes, OsDREB1C, E, and G, in the chilling sensitive rice plants. Their loss of function (LOF) mutants were each more chilling susceptible compared to the wild type, and the LOF mutants of all three genes, dreb1ceg, were more chilling susceptible than any of the single mutants. Strikingly, these mutants were capable of cold acclimation, indicating that these rice DREB1 genes are important for basal chilling tolerance but not cold acclimation. Transcriptome and physiology analyses suggest that the OsDREB1C/E/G genes are involved in reactive oxygen species (ROS) scavenging and cell death regulation under chilling. Furthermore, these three rice DREB1 genes are found to promote tolerance to other abiotic stresses: the OsDREB1C/E/G genes are positive regulators of heat tolerance, OsDREB1C and OsDREB1G are positive regulators of salt tolerance, and OsDREB1G is a positive regulator of drought tolerance. These findings expand our knowledge of the roles of DREB1 proteins in plants, enhance our mechanistic understanding of abiotic stress tolerance and will facilitate the generation of stress-tolerant crop plants.

Exogenous Salicylic Acid Improves Chilling Tolerance in Maize Seedlings by Improving Plant Growth and Physiological Characteristics

Maize (Zea mays L.) is a chilling-sensitive plant. Chilling stress in the early seedling stage seriously limits the growth, development, productivity and geographic distribution of maize. Salicylic acid (SA) is a plant growth regulator involved in the defenses against abiotic and biotic stresses as well as in plant development. However, the physiological mechanisms underlying the effects of foliar applied SA on different maize inbred lines under chilling stress are unclear. Two inbred lines, cold-sensitive cv. C546 and cold-tolerant cv. B125, were used to study the effects of SA on the growth and physiology of maize seedlings. The results showed that the application of SA at 50 mg/L on the leaves of maize seedlings under 4 °C decreased the relative electrolyte conductivity (REC) and the malondialdehyde (MDA) and reactive oxygen species (ROS) (H2O2 and O2−) content due to increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activity; SA also improved photosynthesis in the seedlings through increased chlorophyll content, enhanced Pn and Gs, and decreased Ci. SA application also increased the proline content and the relative water content (RWC) in the maize seedlings, thereby improving their osmotic adjustment capacity. The increase rate caused by SA of plant height and dry weight in C546 were 10.5% and 5.4% higher than that in B125 under 4 °C. In conclusion, SA promotes maize seedling growth and physiological characteristics, thus enhancing chilling resistance and the effect of SA on the chilling resistance of cold-sensitive cv. was stronger than that on cold-tolerant cv. at the low temperature.

Salicylhydroxamic Acid-Resistant and Sensitive Components of Respiration in Chilling-Sensitive Plants Subjected to a Daily Short-Term Temperature Drop

Salicylhydroxamic acid (SHAM) is used in studies of plant respiratory metabolism as a specific inhibitor of alternative cyanide-resistant oxidase (AOX). The sensitivity of respiration in intact plant tissues to SHAM provides indirect evidence for electron transport through the AOX-mediated pathway (AOP) in the respiratory electron transport chain. In this study, chilling-sensitive plants (cucumber (Cucumis sativus L.), tomato (Solanum lycopersicum L.), and sweet pepper (Capsicum annuum L.)) were exposed daily to short-term drops of temperature (to 12, 8, 4, and 1°С) by the end of night periods, and the effects of DROP treatments on SHAM-resistant and SHAM-sensitive respiration of leaves were examined. When leaf respiration in cucumber and tomato plants was measured at optimum temperature (25°C), it showed an increase after the DROP treatments; this phenomenon was caused by the activation of SHAM-sensitive respiration ascribed mainly to AOP activity. At low measurement temperature (15°C), the DROP treatments stimulated total respiration and SHAM-resistant respiration of cucumber leaves, which indicates the activation of electron flow through the cytochrome oxidase pathway (COP). Remarkably, the COP activity increased with the severity of DROP treatment. At high temperature (35°C), the respiration of cucumber leaves became less sensitive to SHAM, whereas SHAM-resistant respiration increased with the severity of DROP treatments. The contribution of the SHAM-sensitive component to the total leaf respiration in cucumber increased with the temperature during measurements. Upon changes in temperature, the SHAM-sensitive respiration in cucumber exhibited larger variations than the SHAM-resistant component, which implies a significant contribution of COP to the respiratory chilling tolerance. Our data suggest that although AOP pathway respiration plays an important role in respiratory activity of chilling-sensitive plants, COP pathway is the main mechanism for maintaining the respiration during low-temperature treatments.

Comparative Study of Plant Physiological Responses to Long-Term and Short-Term Daily Exposures to Low Temperature in the Presence of Protein-Synthesis Inhibitors

The role of the protein synthesis system in the physiological responses to cold was assessed in chilling-sensitive (cucumber) and cold-tolerant (wheat) plants with the use of protein-synthesis inhibitors on 80S (cycloheximide, CHX) and 70S (chloramphenicol, CAP) ribosomes. The plants were subjected to a constant low temperature (LT treatment) at 12°C for cucumber and 4°C for wheat. Another regimen (DROP treatment) included a 2-h daily temperature drop to 12°C for cucumber and 4°C for wheat at the end of the night. Both inhibitors were found to suppress plant leaf growth under any temperature regimen, including the control (at a constant temperature of 23°C). They also reduced the rates of net photosynthesis, transpiration, dark respiration, and chlorophyll accumulation in all treatments but to a larger degree in the control and DROP-treated plants. The results confirmed the previously established dependence of enhanced cold tolerance on protein biosynthesis on 70S and, especially, 80S ribosomes in the LT-treated plants. It was demonstrated for the first time that the protein synthesis system is involved in the enhancement of plant cold tolerance afforded by short-term daily temperature drops. Temperature drops often occur under natural conditions and are used to reduce stem elongation in greenhouse production as an alternative to the use of retardants. The reported data are novel in that the enhanced cold tolerance of DROP-treated plants is accounted for not only by de novo protein synthesis but also by adaptive posttranslational control.

Effects of a Daily Short-Term Temperature Drop on Chilling-Sensitive and Cold-Resistant Plants

A set of physiological and biochemical parameters (leaf growth rate, plant biomass, chlorophyll content, rates of photosynthesis and transpiration, relative water content, leakage of electrolytes, lipid peroxidation intensity, and leaf cold tolerance) were examined with the example of typical cold-resistant (wheat, Triticum aestivum L.) and chilling-sensitive (cucumber, Cucumis sativus L.) plants subjected daily to a short-term temperature drop (DROP treatments) under controlled environmental conditions. For comparison, the plant responses to prolonged chilling were studied with the same species. To accomplish these aims, the cucumber and wheat plants were subjected to: (a) continuous (round-the-clock) cooling at 4°C (wheat), 9°C (cucumber), and 12°C (wheat and cucumber); (b) short-term (3 h) daily cooling to the same temperatures at the end of night periods over 6 days. Although cold-resistant and chilling-sensitive plants showed quantitatively and qualitatively different responses during and after long-term cooling, the plant responses to DROP treatments were qualitatively similar and differed only in their extent depending on cooling temperature. The DROP treatments retarded linear growth of plant organs in both chilling-sensitive and cold-resistant species. They also induced a range of favorable physiological changes promoting plant capability of adaptation. Specifically, photosynthetic rates in DROP-treated plants at chilling temperatures were higher than in untreated plants. In addition, DROP treatments improved the plant chilling tolerance.

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).

Influence of Daily Short-Term Temperature Drops on Respiration to Photosynthesis Ratio in Chilling-Sensitive Plants

Cucumber (Cucumis sativus L.), tomato (Solanum lycopersicum L.), and sweet pepper (Capsicum annuum L.) plants were subjected daily over 13 days to short-term (2 h) temperature drops to 12, 8, 4, and 1°C (DROP treatments) at the end of night periods, and effects of these chilling treatments on the ratio of dark respiration in leaves (Rd) to gross photosynthesis (Ag) were examined. The results showed that DROP treatments affected the Rd/Ag ratio in leaves: this ratio increased significantly in cucumber and tomato plants and was slightly affected in pepper plants. When the temperature drops to 12°C were applied, the increase in Rd/Ag ratio in cucumber and tomato plants was entirely due to the rise in Rd. In the case of temperature drops to 8°C and below, the increase in Rd/Ag was determined by both elevation of Rd and the concurrent decrease in Ag. In cucumber plants, the extent of Ag and Rd changes increased with the DROP severity, i.e., with lowering the temperature of DROP treatment. The inhibition of photosynthesis by DROP treatment in cucumber plants was accompanied by the diminished efficiency of light energy use for photosynthesis and by the increase in the light compensation point. The elevation in Rd/Ag ratio in cucumber plants was accompanied by the decline in growth characteristics, such as accumulation of aboveground biomass, plant height, and leaf area. It was concluded that the R/A ratio is an important indicator characterizing the adaptive potential of chilling-sensitive plant species and their response to daily short-term temperature drops.

Constitutive expression of CaHSP22.5 enhances chilling tolerance in transgenic tobacco by promoting the activity of antioxidative enzymes.

Chilling stress limits the productivity and geographical distribution of many organisms throughout the world. In plants, the small heat shock proteins (sHSPs) belong to a group of proteins known as chaperones. The sweet pepper (Capsicum annuum L.) cDNA clone CaHSP22.5, which encodes an endoplasmic reticulum-located sHSP (ER-sHSP), was isolated and introduced into tobacco (Nicotiana tabacum L.) plants and Escherichia coli. The performance index and the maximal efficiency of PSII photochemistry (Fv/Fm) were higher and the accumulation of H2O2 and superoxide radicals (O2-) was lower in the transgenic lines than in the untransformed plants under chilling stress, which suggested that CaHSP22.5 accumulation enhanced photochemical activity and oxidation resistance. However, purified CaHSP22.5 could not directly reduce the contents of H2O2 and O2- in vitro. Additionally, heterologously expressed recombinant CaHSP22.5 enhanced E. coli viability under oxidative stress, helping to elucidate the cellular antioxidant function of CaHSP22.5 in vivo. At the same time, antioxidant enzyme activity was higher, which was consistent with the lower relative electrolyte conductivity and malondialdehyde contents of the transgenic lines compared with the wild-type. Furthermore, constitutive expression of CaHSP22.5 decreased the expression of other endoplasmic reticulum molecular chaperones, which indicated that the constitutive expression of ER-sHSP alleviated endoplasmic reticulum stress caused by chilling stress in plants. We hypothesise that CaHSP22.5 stabilises unfolded proteins as a chaperone and increases the activity of reactive oxygen species-scavenging enzymes to avoid oxidation damage under chilling stress, thereby suggesting that CaHSP22.5 could be useful for improving the tolerance of chilling-sensitive plant types.

The effect of Trichoderma harzianum in mitigating low temperature stress in tomato ( Solanum lycopersicum L.) plants

Abstract Most tomato cultivars are considered as chilling-sensitive plants and the chilling stress prevalent in many regions of the northern hemisphere limits their culture. Some plant-symbiotic strains of the genus Trichoderma colonize plant roots and induce significant changes in plant gene expression leading to enhanced growth, especially under biotic and abiotic stresses. In this study, the effects of Trichoderma harzianum AK20G strain (Th), as a bio-control agent, was investigated on the tolerance of tomato (Solanum lycopersicum L.) plants under chilling stress. Tomato plants were exposed to low temperatures after being inoculated with “Th” and their physiological, biochemical and molecular responses were investigated at different time courses. Results showed that “Th” have efficiently alleviated the adverse effects of cold stress leading to enhanced photosynthetic and growth rates. It was also revealed that “Th” reduced the lipid peroxidation rate and electrolyte leakage while increasing leaf water content and proline accumulation. Gene expression analysis revealed that the expression of transcription factor NAC1 and dehydrin TAS14 was drastically surged after cold treatment while P5CS expression was decreased with continuation of the cold stress. Interestingly, “Th” improved the expression of TAS14 and P5CS and their expression increased with the time during the experiment. The findings of the present study provide a detailed insight into the physio-biochemical and molecular processes leading to low temperature tolerance in T. harzianum-inoculated tomato plants.

The effects of chilling-light stress on photosystems I and II in three Paphiopedilum species

BackgroundLow temperatures pose a critical limitation to the physiology and survival of chilling-sensitive plants. One example is the genus Paphiopedilum (Orchidaceae), which is mainly native to tropical and subtropical areas from Asia to the Pacific islands. However, little is known about the physiological mechanism(s) underlying its sensitivity to chilling temperature. We examined how chilling-light stress influences the activities of photosystem I (PSI) and photosystem II (PSII) in three species: P. armeniacum, P. micranthum, and P. purpuratum. All originate from different distribution zones that cover a range of temperatures.ResultsPhotosystem II of three Paphiopedilum species was remarkable sensitivity to chilling stress. After 8 h chilling stress, the maximum quantum yield of PSII of three species of Paphiopedilum was significantly decreased, especially in P. purpuratum. The quantity of efficient PSI complex (Pm) value did not significantly differ after 8 h chilling treatment compared to the original value in three species. The stronger PSII photoinhibition and significantly less capacity for cyclic electron flow (CEF) were observed in P. purpuratum.ConclusionsIn conclusion, the three species of Paphiopedilum showed significant PSII photoinhibition when exposed to 4 °C chilling treatment. However, their PSI activities were not susceptible to chilling-light stress during 8 h. The CEF was important for the photoprotection of PSI and PSII in P. armeniacum and P. micranthum under chilling conditions. Our findings suggested that the photosynthetic characteristics of Paphiopedilum were well adapted to their habitat.

Plasticity in roles of cyclic electron flow around photosystem I at contrasting temperatures in the chilling-sensitive plant Calotropis gigantea

Cyclic electron flow (CEF) around photosystem I is thought to balance the ATP/NADPH energy budget and protect photosynthetic apparatus. However, the plasticity in roles of CEF at contrasting temperatures is not well understood. We examined photosynthetic electron flow, non-photochemical quenching (NPQ), PSI redox state, and electrochromic shift (ECS) signal at 25°C (normal temperature) and 4°C (low temperature) for leaves of a chilling-sensitive tree species Calotropis gigantea. We found that electron flow through PSII (ETRII) was largely depressed at 4°C irrespective of light condition, whereas CEF was enhanced under light intensities below 500μmol photons m−2s−1 but suppressed under light intensities above 760μmol photons m−2s−1. Meanwhile, both NPQ and PSI donor side limitation [Y(ND)] were enhanced at 4°C. Moreover, the relationships between the rate of CEF and values for NPQ and Y(ND) changed between 4°C and 25°C. At low temperature, the proton gradient across thylakoid membranes (ΔpH) was enhanced and the thylakoid proton conductivity was depressed. Based on these results, we propose that, at normal growth temperature such as 25°C, CEF contributes mainly to the balancing of ATP/NADPH energy budget required by primary metabolism. In contrast, at low temperature such as 4°C, the main function of the CEF-dependent proton motive force is lumenal acidification, favoring photoprotection for photosynthetic apparatus. The plasticity in roles of CEF at contrasting temperatures may be regulated by the activity of thylakoid ATP synthase.

Mutations in the Prokaryotic Pathway Rescue the fatty acid biosynthesis1 Mutant in the Cold

The Arabidopsis (Arabidopsis thaliana) fatty acid biosynthesis1 (fab1) mutant has increased levels of the saturated fatty acid 16:0 due to decreased activity of 3-ketoacyl-acyl carrier protein (ACP) synthase II. In fab1 leaves, phosphatidylglycerol, the major chloroplast phospholipid, contains up to 45% high-melting-point molecular species (molecules that contain only 16:0, 16:1-trans, and 18:0), a trait associated with chilling-sensitive plants, compared with less than 10% in wild-type Arabidopsis. Although they do not exhibit typical chilling sensitivity, when exposed to low temperatures (2°C-6°C) for long periods, fab1 plants do suffer collapse of photosynthesis, degradation of chloroplasts, and eventually death. A screen for suppressors of this low-temperature phenotype has identified 11 lines, some of which contain additional alterations in leaf-lipid composition relative to fab1. Here, we report the identification of two suppressor mutations, one in act1, which encodes the chloroplast acyl-ACP:glycerol-3-phosphate acyltransferase, and one in lpat1, which encodes the chloroplast acyl-ACP:lysophosphatidic acid acyltransferase. These enzymes catalyze the first two steps of the prokaryotic pathway for glycerolipid synthesis, so we investigated whether other mutations in this pathway would rescue the fab1 phenotype. Both the gly1 mutation, which reduces glycerol-3-phosphate supply to the prokaryotic pathway, and fad6, which is deficient in the chloroplast 16:1/18:1 fatty acyl desaturase, were discovered to be suppressors. Analyses of leaf-lipid compositions revealed that mutations at all four of the suppressor loci result in reductions in the proportion of high-melting-point molecular species of phosphatidylglycerol relative to fab1. We conclude that these reductions are likely the basis for the suppressor phenotypes.

Lipid response to short-term chilling shock and long-term chill hardening in Jatropha curcas L. seedlings

Low non-freezing temperature is one of the major environmental factors that affect metabolism, growth, development and geographical distribution of chilling-sensitive plants, Jatropha curcas, a chilling-sensitive plant, which is considered as a sustainable energy plant with great potential for biodiesel production. Our previous studies showed that short-term chilling shock at 5 °C for 4 h and long-term chill hardening at 12 °C 1 or 2 days could improve chilling tolerance of J. curcas seedlings, but lipidomic response to chilling shock and chill hardening has not been elucidated. In this study, membrane lipid composition change in J. curcas seedlings during chilling shock and chill hardening was investigated by liquid chromatography-electrospray ionization-mass spectrometry (LC–ESI–MS) approach. The results indicated that the relative abundances of nine classes and 72 species of membrane lipids, such as phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylinositol (PI), lysophosphatidylcholine (lysoPC) and lysophosphatidylglycerol (lysoPG), two glycolipids digalactosyldiacylglycerol (DGDG) and monogalactosyldiacylglycerol (MGDG) and a sulfoquinovosyldiacylglycerol (SQDG), were significantly changed, and the degree of unsaturation of above-mentioned cellular membrane lipids with fatty acid differing in chain lengths and the number of double bonds also increased in varying degrees during chilling shock and chill hardening. These results suggested that remodeling and increase in the degree of unsaturation of membranes lipids may be a common physiological basis for short-term chilling shock- and long-term chill hardening-induced chilling tolerance of J. curcas seedlings.

Overexpression of tomato GDP-L-galactose phosphorylase gene in tobacco improves tolerance to chilling stress.

The overexpression of tomato GDP- l -galactose phosphorylase gene enhanced tolerance to chilling stress and reduced photoinhibition of photosystems I and II in transgenic tobacco. Chilling stress is a crucial factor that limits the geographical distribution and yield of chilling-sensitive plants. Ascorbate (AsA) protects plants by scavenging reactive oxygen species and reduces photoinhibition by promoting the conversion of violaxanthin to zeaxanthin in the xanthophyll cycle to dissipate excess excitation energy. Possible mechanisms of AsA for plant photoprotection under chilling stress were investigated by isolating the tomato GDP-L-galactose phosphorylase gene (SlGGP) and producing transgenic tobacco plants with overexpression of SlGGP. The transgenic plants subjected to chilling stress accumulated less H(2)O(2), demonstrated lower levels of ion leakage and malondialdehyde, and acquired higher net photosynthetic rate, higher maximum photochemical efficiency of PSII, and higher D1 protein content compared with the wild-type (WT) plants. The transgenic plants subjected to chilling stress also showed higher GDP-L-galactose phosphorylase activity, increased AsA content as well as ascorbate peroxidase and oxidizable P700 activities than WT plants. Thus, SlGGP overexpression is crucial in promoting AsA synthesis and alleviating photoinhibition of two photosystems.

Involvement of compatible solutes in chill hardening-induced chilling tolerance in Jatropha curcas seedlings

Low temperature is a major environmental factor that affects metabolism, growth, development, distribution and production of chilling-sensitive plant, and J. curcas L. is a sustainable energy plant with great potential for biodiesel production due to the fact that its seed contains high oil content, which has attracted much attention worldwide. Our previous work found that the chill hardening improved the chilling tolerance of J. curcas seedlings (Ao et al. in Acta Physiologiae Plantarum 35:153–160, 2013), but its mechanism still remains elusive. In present work, the mechanism of chill hardening-induced chilling tolerance was further investigated in J. curcas seedlings. The results showed that chill hardening at 12 °C for 2 days markedly lowered osmotic and water potentials, which, in turn, maintained relative higher pressure potential in leaves of J. curcas seedlings compared with the control seedlings without chill hardening. In addition, chill hardening gradually increased compatible solutes proline, betaine and total soluble sugar contents compared with the control. When the control and hardened seedlings were subjected to chilling stress at 1 °C for 1–7 days, the chill-hardened seedlings significantly accumulated higher proline, betaine and total soluble sugar contents, which decreased osmotic and water potentials, and maintained higher pressure potential. To further understand the pathways of accumulation of compatible solutes, measurement of activities of ∆1-pyrroline-5-carboxylate synthetase (P5CS), glutamate dehydrogenase (GDH), ornithine aminotransferase (OAT), arginase, proline dehydrogenase (ProDH) and betaine dehydrogenase (BADH) showed that the chill hardening at 12 °C for 2 days obviously increased the activities of P5CS, GDH, OAT, arginase and BADH, as well as lowered ProDH activity both in leaves and stems of J. curcas seedlings to some extent as compared with the control. When the control and hardened seedlings were exposed to chilling stress at 1 °C for 1–7 days, the chill-hardened seedlings generally maintained significantly higher activities of P5CS, GDH, OAT, arginase and BADH. All above-mentioned results illustrated that the chill hardening could induce an accumulation of compatible solutes in leaves of J. curcas seedlings and compatible solutes play important roles in chill hardening-induced chilling tolerance.

Combined action of antioxidant defense system and osmolytes in chilling shock-induced chilling tolerance in Jatropha curcas seedlings

Low non-freezing temperature is one of the major environmental factors affecting growth, development and geographical distribution of chilling-sensitive plants, Jatropha curcas is considered as a sustainable energy plants with great potential for biodiesel production. In this study, chilling shock at 5 °C followed by recovery at 26 °C for 4 h significantly improved survival percentage of J. curcas seedlings under chilling stress at 1 °C. In addition, chilling shock could obviously enhance the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR), and the levels of antioxidants ascorbic acid (AsA) and glutathione (GSH), as well as the contents of osmolytes proline and betaine in leaves of seedlings of J. curcas compared with the control without chilling shock. During the process of recovery, GR activity, AsA, GSH, proline and betaine contents sequentially increased, whereas SOD, APX and CAT activities gradually decreased, but they markedly maintained higher activities than those of control. Under chilling stress, activities of SOD, APX, CAT, GR and GPX, and contents of AsA, GSH, proline and betaine, as well as the ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)] in the shocked and non-shock seedlings all dropped, but shocked seedlings sustained significantly higher antioxidant enzyme activity, antioxidant and osmolyte contents, as well as ratio of reduced antioxidants to total antioxidants from beginning to end compared with control. These results indicated that the chilling shock followed by recovery could improve chilling tolerance of seedlings in J. curcas, and antioxidant enzymes and osmolytes play important role in the acquisition of chilling tolerance.

Chilling Tolerance Improving of Watermelon Seedling by Salicylic Acid Seed and Foliar Application

Chilling temperatures lead to numerous physiological disturbances in the cells of chilling-sensitive plants and result in chilling injury and death of tropical and subtropical plants such as watermelon. In this study, the possibility of cold stress tolerance enhancing of watermelon seedling (Citrullus lanatus) by exogenous application of Salicylic acid (SA) was investigated. SA was applied through seed soaking or foliar spray at 0, 0.5, 1 and 1.5 mM concentration. After SA treatment, the seedlings were subjected to chilling 5 h/day at 4°C for 5 days. Statistical analysis showed significant effects of the application methods and SA concentrations on plant growth parameters, photosynthetic pigments, electrolyte leakage, proline and chilling injury index. SA application improved growth parameters and increased chlorophyll content of watermelon seedling subjected to chilling stress and provided significant protection against chilling stress compared to non-SA-treated seedlings. Although two SA application methods improved chilling stress tolerance, seed soaking method provided better protection compared to foliar spray method. SA ameliorated the injury caused by chilling stress via inhibiting proline accumulation and leaf electrolyte leakage. The highest cold tolerance was obtained with 0.5 mM SA application. Results indicate that SA could be used effectively to protect watermelon seedling from damaging effects of chilling stress at the early stages of growth.

Analysis of the Cold-Responsive Transcriptome in the Mature Pollen of Arabidopsis

Mature pollen is very sensitive to cold stress in chilling-sensitive plants. To understand the genetic regulation of tolerance to cold stress, we analyzed the transcript expression profile in mature pollen of Arabidopsis using Affymetrix GeneChips containing ∼24,000 genes. Expression of 2,127 genes was cold-regulated, of which 697 genes were upregulated and 1,430 genes were downregulated. Further analysis showed that a large number of signal transduction components were significantly affected by cold treatment, indicating extensive changes in the gene regulatory networks of mature pollen. Many cold-responsive genes encode transcription factors, suggesting a multitude of transcriptional cascades. A number of genes important for the biosynthesis or signaling of plant hormones, such as abscisic acid, auxin, and jasmonate, were regulated by cold stress, which is of potential importance in coordinating cold tolerance with pollen growth and development. In addition, 159 mature pollen-specific genes that might be involved in pollen viability were also cold-regulated. Expression of the cold-responsive transcripts identified by microarray analysis was confirmed by quantitative real-time PCR. Our study provides an overall picture of the cold-responsive transcriptome in Arabidopsis pollen and is valuable for understanding gene regulation in response to cold stress and the molecular mechanisms of cold tolerance in mature pollen.