Dark chilling effects on soybean genotypes during vegetative development: parallel studies of CO2 assimilation,chlorophyll a fluorescence kinetics O-J-I-P and nitrogen fixation

The effects of dark chilling on CO2 assimilation, chlorophyll a fluorescence kinetics and nitrogen fixation were compared in two Glycine max (L.) Merr. genotypes. The aim was to elucidate the mechanisms by which photosynthesis was inhibited as well as identification of selection criteria for dark chilling tolerance. Seedlings were dark chilled (8 degrees C) for 9 consecutive nights but kept at normal day temperatures (28 degrees C). CO2 gas exchange analysis indicated that photosynthesis in Maple Arrow was inhibited largely as a result of stomatal limitation, while in Fiskeby V, it indicated inhibition of the mesophyll reactions. Increased intercellular CO2 concentration and decreased carboxylation efficiency suggested loss of Rubisco activity in Fiskeby V, although no effect on the KM (CO2) of Rubisco was observed. Quantification and deconvolution of the Chl a fluorescence transients into several phenomenological and biophysical parameters (JIP-test) revealed large genotypic differences in the response of PSII to dark chilling. These parameters differentially changed in the two genotypes during the progression of the chilling treatment. Among them, the performance index, reflecting several responses of the photochemical apparatus, provided the best preliminary overall assessment of the genotypes. In contrast, the quantum yield of primary photochemistry varphiPo (FV/FM) was quite insensitive. The recovery of most of the JIP-test parameters in Maple Arrow after 6 and 9 nights of dark chilling was a major genotypic difference. Genotypic differences were also observed with regard to the ureide response and N2 fixation appeared to be more sensitive to dark chilling than CO2 assimilation. The JIP-test provided information consistent with results derived from CO2 assimilation and N2 fixation studies suggesting that it can substitute the much more time-consuming methods for the detection of chilling stress and can well satisfy the requirements of a rapid and accurate screening method.     

Limitation of photosynthetic carbon metabolism by dark chilling in temperate and tropical soybean genotypes.

In the experiments reported in this paper, we characterised the physiological and biochemical factors involved in the chilling-induced inhibition of photosynthetic carbon metabolism in soybean [Glycine max (L.) Merr.] genotypes of temperate and tropical adaptation. Plants of Maple Arrow (temperate genotype) and Java 29 (tropical genotype) were exposed to a single night at 8 degrees C. Dark chilling resulted in the inhibition of diurnal CO2 assimilation rate and decreased stomatal conductance in both genotypes. Further analysis, however, revealed a difference in the response of the two genotypes. Stomatal limitation was largely responsible for the inhibition of CO2 assimilation in Maple Arrow, whereas mesophyll limitation dominated the inhibition in Java 29. The results indicate that inhibition of stromal fructose-1,6-bisphosphatase (sFBPase; EC 3.1.3.11) activity and impaired electron transport capacity were responsible for the decrease in ribulose-1,5-bisphosphate (RuBP) regeneration capacity in Java 29. Sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity was progressively inhibited during the light period in this genotype and might impose an additional constraint on photosynthesis. Maple Arrow appears to possess, at least with respect to photosynthetic carbon metabolism, physiological and biochemical characteristics that contribute towards its superior dark chilling tolerance.     

Drought enhances maize chilling tolerance. II. Photosynthetic traits and protective mechanisms against oxidative stress

In the present research we studied the photosynthetic traits and protective mechanisms against oxidative stress in two maize ( Zea mays L.) genotypes differing in chilling sensitivity (Z7, tolerant and Penjalinan, sensitive) subjected to 5°C for 5 days, with or without pretreatment by drought. The drought pretreatment decreased the symptoms of chilling injury in Penjalinan plants estimated as necrotic leaf area and maximum quantum yield of photosystem II. Furthermore, drought pretreatment diminished the level of lipid peroxidation caused by chilling in Penjalinan plants. After one day of recovery from chilling the Z7 and drought-pretreated Penjalinan plants showed higher net photosynthesis rates than the non-drought-pretreated Penjalinan plants, thereby decreasing the probability of generating reactive oxygen species. The greater net photosynthesis was correlated with the greater NADP-malate dehydrogenase activity. No differences in either the de-epoxidation state of the xanthophyll cycle or the antioxidant enzyme activities were found among the chilled groups of plants. However, a drastic decrease in ascorbate content was observed in chilled Penjalinan plants without drought pretreatment. As we found an increase of H₂O₂ content after drought pretreatment, we suggest its involvement as a signal in the drought-enhanced chilling tolerance of maize.     

Protein synthesis and phospholipids in soybean axes in response to imbibitional chilling

The responses of two cultivars of soybean (Merr.) to a chilling treatment (4 C for first hour of imbibition) were compared. The germination of cv. Biloxi was unaffected by the treatment, while the germination of cv. Fiskeby was reduced. The phospholipid fatty acids of dry axes of the two cultivars were very similar, and, thus, could not be correlated with their responses to chilling. The fatty acid composition of chilling-tolerant Biloxi did not change over a subsequent 23-hour warm incubation, but there was a marked reduction in the unsaturated fatty acids of chilling-sensitive Fiskeby after 12 hours, which may be a symptom of deterioration. Protein synthesis in both cultivars was reduced by the chilling treatment. Redrying of Biloxi axes up to 18 hours after the onset of imbibition had no effect on their germination upon rehydration. Germination of Fiskeby axes was reduced by redrying after 8 hours of imbibition. After 7 months of dry storage of intact seeds, the sensitivity of the axes to chilling was retested. Biloxi axes had become chilling-sensitive, while the germination of Fiskeby axes was reduced to zero by the chilling treatment. A hypothesis is presented that imbibitional chilling sensitivity is an indication of reduced vigor, axes with a high vigor can tolerate the stress, while those without cannot.     

Sink removal and leaf senescence in soybean : cultivar effects

Three cultivars of soybean (Glycine max [L.] Merr. cvs Harper, McCall, and Maple Amber) were grown in the field and kept continuously deflowered throughout the normal seedfill period. For all cultivars, deflowering led to delayed leaf abscission and a slower rate of chlorophyll loss. Compared to control plants, photosynthesis and ribulose 1,5-bis-phosphate carboxylase/oxygenase (Rubisco) level declined slightly faster for deflowered Harper, but for both McCall and Maple Amber, leaves of deflowered plants maintained approximately 20% of maximum photosynthesis and Rubisco level 1 month after control plants had senesced. Deflowering led to decreased leaf N remobilization and increased starch accumulation for all cultivars, but cultivars differed in that for McCall and Maple Amber, N and starch concentrations slowly but steadily declined over time whereas for Harper, N and starch concentrations remained essentially constant over time. SDS-PAGE of leaf proteins indicated that for all cultivars, deflowering led to accumulation of four polypeptides (80, 54, 29, and 27 kilodaltons). Western analysis using antisera prepared against the 29 and 27 kilodalton polypeptides verified that these polypeptides were the glycoproteins previously reported to accumulate in vacuoles of paraveinal mesophyll cells of depodded soybean plants. The results indicated that depending on the cultivar, sink removal can lead to either slightly faster or markedly slower loss of photosynthesis and Rubisco. This difference, however, was not associated with the ability to synthesize leaf storage proteins. For any particular cultivar, declines in chlorophyll, photosynthesis, and Rubisco were initiated at approximately the same time for control and deflowered plants. Thus, even though cultivars differed in rate of decay of photosynthetic rate and Rubisco level in response to sink removal, the initiation of leaf senescence was not influenced by presence or absence of developing fruits.     

Responses of pomegranate cultivars to severe water stress and recovery: changes on antioxidant enzyme activities,gene expression patterns and water stress responsive metabolites

The biochemical and molecular responses of five commercially well-known pomegranate cultivars to severe water stress were studied. The cultivars were subjected to 14-day water stress by withholding irrigation, followed by re-watering for 7 days. Results showed clear differences in metabolites contents and activities of antioxidant enzymes among various pomegranate cultivars during severe water stress and recovery. According to our results, increased accumulation of proline in pomegranate was not related to osmotic adjustment during severe water stress. Except for ‘Ghojagh’, leaves grown under severe water stress conditions showed symptoms of oxidative stress such as reduced chlorophyll concentration. The improved performance of ‘Ghojagh’ under drought stress may be associated with an efficient osmotic adjustment. The up- or down regulated expression of cytosolic glutathione reductase (cytosolic GR) and glutathione peroxidase were observed under drought conditions. Moreover, the suppressed expression of cytosolic GR was also noted. Comparatively, ‘Rabab’ exhibited higher antioxidant capacity and an efficient ROS-scavenging mechanism under drought stress. Lower levels of membrane lipid peroxidation in ‘Ghojagh’ and ‘Rabab’ under drought stress and the marked reduction of malondialdehyde concentration after re-watering represents that these cultivars have a good tolerance to drought stress. As a first step towards the study of the biochemical and molecular responses of pomegranate plants to water stress, this research provides new information into the mechanisms of drought tolerance in the plants.     

Differential responses of antioxidative system to chilling and drought in four rice cultivars differing in sensitivity

Responses of antioxidative defense systems to chilling and drought stresses were comparatively studied in four cultivars of rice (Oryza sativa L.) differing in sensitivity, two of them (Xiangnuo no. 1 and Zimanuo) are tolerant to chilling but sensitive to drought and the other two (Xiangzhongxian no. 2 and IR50) are tolerant to drought but sensitive to chilling. The seedlings of rice were transferred into growth chamber for 5 d at 8 degrees C as chilling treatment, or at 28 degrees C as control, or at 28 degrees C but cultured in 23% PEG-6000 solution as drought stress treatment. Under drought stress the elevated levels of electrolyte leakage, contents of H(2)O(2) and total thiobarbituric acid-reacting substances (TBARS) in Xiangzhongxian no. 2 and IR50 are lower than those in Xiangnuo no. 1 and Zimanuo. On the contrary, Xiangnuo no. 1 and Zimanuo have much lower level of electrolyte leakage, H(2)O(2) and TBARS than Xiangzhongxian no. 2 and IR50 under chilling stress. Activities of antioxidant enzymes (superoxide dismutase (SOD), catalase, and ascorbate-peroxidase (APX)) and contents of antioxidants (ascorbaic acid and reduced glutathione) were measured during the stress treatments. All of them were enhanced greatly until 3 d after drought stress in the two drought-tolerant cultivars, or after chilling stress in the two chilling-tolerant cultivars. They all were decreased at 5 d after stress treatments. On the other hand, activities of antioxidant enzymes and contents of antioxidants were decreased greatly in the drought-sensitive cultivars after drought stress, or in the chilling-sensitive cultivars after chilling stress. The results indicated that tolerance to drought or chilling in rice is well associated with the enhanced capacity of antioxidative system under drought or chilling condition, and that the sensitivity of rice to drought or chilling is linear correlated to the decreased capacity of antioxidative system.     

塔里木沙漠公路防护林3种植物光合特性对干旱胁迫的响应

利用Li-6400光合作用系统在沙漠腹地测定分析塔里木沙漠公路防护林植物梭梭(Haloxylon ammodendron)、多枝柽柳(Tamarix ramosissima)和乔木状沙拐枣(Calligonum arborescens)光合特性对干旱胁迫的响应,探讨了水分亏缺对防护林植物光合积累的影响作用。结果显示:沙拐枣的净光合速率、蒸腾速率、水分利用效率、光能利用效率及潜在光合作用能力对水分亏缺最敏感,而柽柳则最不敏感;不同处理下3种植物光合特性变化的差异表明,不同植物对水分亏缺有着不同的响应变化和适应方式;此外,干旱胁迫未提高3种植物的水分利用效率,反而降低了其光能利用效率;C3植物多枝柽柳在干旱高温条件下保持着比C4植物梭梭和沙拐枣更为稳定的光合积累和水分利用效率,说明部分C3植物具备不弱于C4荒漠植物的干旱耐受适应能力;虽然水分亏缺对3种植物的光合作用能力均存在不同程度抑制作用,但未对其光合积累造成不可逆转的影响。可见3种植物都有很强的干旱适应与耐受能力,这种能力表明沙漠公路防护林的灌溉管理还有进一步的节水空间。     

Dark chilling increases glucose-6-phosphate dehydrogenase activity in soybean leaves

Available evidence suggests that the stress‐induced increase in the activity of glucose‐6‐phosphate dehydrogenase (G6PDH, EC 1.1.1.49), the key regulatory enzyme of the oxidative pentose phosphate pathway, might often be related to the presence of plant water deficit. The response of G6PDH to dark chilling in chilling sensitive plant species is still unknown. In this communication we report on this response and its dependence on the presence of chill‐induced drought stress. A chilling sensitive soybean (Glycine max L. Merr.) genotype was exposed to dark chilling of the entire plant (whole‐chilled) or only the shoots and leaves (shoot‐chilled). The development of chill‐induced drought stress upon illumination was quantified by measurement of proline and relative water content (RWC). Chill‐induced drought stress (decrease in RWC and increase in proline content) developed with time in whole‐chilled plants, but not in shoot‐chilled plants. The response of the above‐mentioned treatments on G6PDH activity in fully expanded leaves was assessed. In parallel, the effects on CO₂ assimilation, PSII activity and chloroplast fructose‐1,6‐bisphosphatase (FBPase EC 3.1.3.11) and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco EC 4.1.1.39) activity were quantified. A decrease in CO₂ assimilation rate, FBPase activity and ribulose‐1,5‐bisphosphate (RuBP) content was observed in whole‐chilled but not in shoot‐chilled plants. However, in shoot‐chilled plants regulation of diurnal PSII activity was altered. The increase in the activation state of NADP‐dependent malate dehydrogenase (NADP‐MDH EC 1.1.1.82) in shoot‐chilled plants suggests an increase in stromal redox state. Although the two different dark chilling treatments resulted in distinct physiological and biochemical effects, both induced an increase in foliar G6PDH activity, suggesting an important role of this enzyme during and following dark chilling stress, irrespective of the presence of chill‐induced drought stress.     

A Comparison of the Effects of Chilling on Leaf Gas Exchange in Pea (Pisum sativum L.) and Cucumber (Cucumis sativus L.)

The effects of chilling on the photosynthesis of a chilling-resistant species, pea (Pisum sativum L. cv Alaska) and a chilling-sensitive species, cucumber (Cucumis sativus L. cv Ashley) were compared in order to determine the differences in the photosynthetic chilling sensitivity of these two species. For these experiments, plants were chilled (5°C) for different lengths of time in the dark or light. Following a 1 hour recovery period at 25°C, photosynthetic activity was measured by gas exchange (CO₂ uptake and H₂O release), quantum yield, and induced chlorophyll fluorescence. The results show that pea photosynthesis was largely unaffected by two consecutive nights of chilling in the dark, or by chilling during a complete light and dark cycle (15 hours/9 hours). Cucumber gas exchange was reduced by one night of chilling, but its quantum yield and variable fluorescence were unaffected by dark chilling. However, chilling cucumber in the light led to reduced CO₂ fixation, increased internal leaf CO₂ concentration, decreased quantum yield, and loss of variable fluorescence. These results indicate that chilling temperatures in conjunction with light damaged the light reactions of photosynthesis, while chilling in the dark did not.     

Co‐expression of NCED and ALO improves vitamin C level and tolerance to drought and chilling in transgenic tobacco and stylo plants

Abscisic acid (ABA) regulates plant adaptive responses to various environmental stresses, while l ‐ascorbic acid (AsA) that is also named vitamin C is an important antioxidant and involves in plant stress tolerance and the immune system in domestic animals. Transgenic tobacco (Nicotiana tabacum L.) and stylo [Stylosanthes guianensis (Aublet) Swartz], a forage legume, plants co‐expressing stylo 9‐cis‐epoxycarotenoid dioxygenase (SgNCED1) and yeast d ‐arabinono‐1,4‐lactone oxidase (ALO) genes were generated in this study, and tolerance to drought and chilling was analysed in comparison with transgenic tobacco overexpressing SgNCED1 or ALO and the wild‐type plants. Compared to the SgNCED1 or ALO transgenic plants, in which only ABA or AsA levels were increased, both ABA and AsA levels were increased in transgenic tobacco and stylo plants co‐expressing SgNCED1 and ALO genes. Compared to the wild type, an enhanced drought tolerance was observed in SgNCED1 transgenic tobacco plants with induced expression of drought‐responsive genes, but not in ALO plants, while an enhanced chilling tolerance was observed in ALO transgenic tobaccos with induced expression of cold‐responsive genes, but not in SgNCED1 plants. Co‐expression of SgNCED1 and ALO genes resulted in elevated tolerance to both drought and chilling in transgenic tobacco and stylo plants with induced expression of both drought and cold‐responsive genes. Our result suggests that co‐expression of SgNCED1 and ALO genes is an effective way for use in forage plant improvement for increased tolerance to drought and chilling and nutrition quality.     

Protein synthesis at low temperatures in two soybean cultivars differing by their cold sensitivity

The effect of low temperatures (14°C/8°C, day/night) on polypeptide synthesis in leaves of two soybean ( Glycine max [L.] Merr.) cvs (Verdon and Maple Arrow) differing in cold sensitivity was investigated. The two cultivars were initially characterized in terms of cold tolerance according to their growth at the young plant stage at 14°C/8°C. Verdon was found to be more tolerant than Maple Arrow. In vivo [³⁵S]-methionine labeled polypeptides were resolved by two-dimensional electrophoresis. Autoradiograms were computer analyzed to evidence and quantify significative changes occurring after 5 days at 14°C/8°C, and to compare the response of the two cultivars. Most of the observed changes were quantitative. The two cultivars essentially exhibited a common modified polypeptide pattern in response to cold temperatures, but the changes were quantitatively more pronounced in the most tolerant cultivar. Computer analysis of two-dimensional electrophoresis gels allowed, for the first time, characterization of cultivar differences in terms of protein pattern under cold conditions.     

Improvement of heat and drought photosynthetic tolerance in wheat by overaccumulation of glycinebetaine

Within their natural habitat, crops are often subjected to drought and heat stress, which suppress crop growth and decrease crop production. Causing overaccumulation of glycinebetaine (GB) has been used to enhance the crop yield under stress. Here, we investigated the response of wheat (Triticum aestivum L.) photosynthesis to drought, heat stress and their combination with a transgenic wheat line (T6) overaccumulating GB and its wild-type (WT) Shi4185. Drought stress (DS) was imposed by controlling irrigation until the relative water content (RWC) of the flag leaves decreased to between 78 and 82%. Heat stress (HS) was applied by exposing wheat plants to 40°C for 4 h. A combination of drought and heat stress was applied by subjecting the drought-stressed plants to a heat stress as above. The results indicated that all stresses decreased photosynthesis, but the combination of drought and heat stress exacerbated the negative effects on photosynthesis more than exposure to drought or heat stress alone. Drought stress decreased the transpiration rate (Tr), stomatal conductance (Gs) and intercellular CO₂ concentration (Ci), while heat stress increased all of these; the deprivation of water was greater under drought stress than heat stress, but heat stress decreased the antioxidant enzyme activity to a greater extent. Overaccumulated GB could alleviate the decrease of photosynthesis caused by all stresses tested. These suggest that GB induces an increase of osmotic adjustments for drought tolerance, while its improvement of the antioxidative defense system including antioxidative enzymes and antioxidants may be more important for heat tolerance.     

Ameliorative Effect of Chlormequat Chloride and IAA on Drought Stressed Plants of <Emphasis Type="Italic">Cymbopogon Martinii</Emphasis> and <Emphasis Type="Italic">C. winterianus</Emphasis>

Responses of Cymbopogon martinii and C. winterianus to drought stress and chlormequat chloride and IAA application are compared. These two species are important source of essential oil production in drought regions. For both species and their cultivars relative water content (RWC), herbage yield and oil amount decreased under drought, while oil biosynthesis increased. Oil concentration increased significantly under drought in C. winterianus while peroxidase activity increased in C. martinii. Amount of geraniol increased under drought stress in C. martinii while citronellal and geraniol accumulation decreased in C. winterianus. Ameliorative effects of chlormequat chloride and IAA were observed in drought stressed plants of both species. Herbage yield increased significantly in chlormequat chloride and IAA treated stressed plants of C. winterianus, while oil concentration increased in C. martinii. Ameliorative effect of IAA in increasing oil yield was significant in drought stressed plants of both the species. Changes in various morpho-physiological traits indicated that chlormequat chloride and IAA can partially alleviate the detrimental effect of drought in these aromatic grasses.     

The role of salicylic acid in response of two rice cultivars to chilling stress

Two rice (Oryza sativa L.) cultivars differing in chilling sensitivity, Changbaijiu (chilling-tolerant) and Zhongjian (chilling-sensitive) were pre-treated with 0.5, 1.0 and 2.0 mM salicylic acid (SA) for 24 h before chilling at 5°C for 1 d. Chilling induced SA accumulation, particularly conjugated SA in both leaves and roots of the two rice cultivars. After SA administration, SA accumulated in the roots of both cultivars at a concentration-dependent manner, whereas only a slight increase was observed in their leaves. Conjugated SA accounted for most of the increase. The beneficial effect of SA treatment on protecting rice seedlings from chilling injury was not observed at any concentration in either cultivar. Pre-treatment with SA even decreased their chilling tolerance confirmed by increased electrolyte leakage and lipid peroxidation. Further, most of the activities of antioxidant enzymes decreased or remained unchanged in leaves and roots of SA pre-treated seedlings after chilling. These results implied that down-regulation of antioxidant defence might be involved in the reduction of chilling tolerance in SA-pre-treated plants.     

Abiotic stress tolerance in transgenic eggplant (Solanum melongena L.) by introduction of bacterial mannitol phosphodehydrogenase gene

In the present work, the bacterial mannitol-1-phosphodehydrogenase(mtlD) gene was introduced into eggplant(Solanummelongena L.) by Agrobacteriumtumefaciens-mediated transformation. Several transformants weregenerated and the transgene integration was confirmed by PCR, dot blot andSouthern blot analysis. Transgenic lines of T₀ and T₁generations were examined for tolerance to NaCl-induced salt stress,polyethylene glycol-mediated drought and chilling stress under bothinvitro and in vivo growth conditions. Aconsiderable proportions of transgenic seeds germinated and seedlings grew wellon 200 mM salt-amended MS basal medium, whereas seeds ofuntransformed control plants failed to germinate. Further, leaf explants fromthe transgenics could grow and showed signs of shoot regeneration onsalt-amended MS regeneration medium, whereas wild type did not respond, and infact the explants showed necrosis and loss of chlorophyll after about one week.The transgenic leaves could also withstand desiccation, and transgenics couldgrow well under chilling stress, and hydroponic conditions with salt stress ascompared to wild type plants. Thus, the transgenic lines were found to betolerant against osmotic stress induced by salt, drought and chilling stress.The morphology of the transgenic plants was normal as controls, but thechlorophyll content was higher in some of the lines. These observations suggestthat mtlD gene can impart abiotic stress tolerance ineggplant.     

Expression profiling of rice cultivars differing in their tolerance to long-term drought stress

Understanding the molecular basis of plant performance under water-limiting conditions will help to breed crop plants with a lower water demand. We investigated the physiological and gene expression response of drought-tolerant (IR57311 and LC-93-4) and drought-sensitive (Nipponbare and Taipei 309) rice (Oryza sativa L.) cultivars to 18 days of drought stress in climate chamber experiments. Drought stressed plants grew significantly slower than the controls. Gene expression profiles were measured in leaf samples with the 20 K NSF oligonucleotide microarray. A linear model was fitted to the data to identify genes that were significantly regulated under drought stress. In all drought stressed cultivars, 245 genes were significantly repressed and 413 genes induced. Genes differing in their expression pattern under drought stress between tolerant and sensitive cultivars were identified by the genotype x environment (G x E) interaction term. More genes were significantly drought regulated in the sensitive than in the tolerant cultivars. Localizing all expressed genes on the rice genome map, we checked which genes with a significant G x E interaction co-localized with published quantitative trait loci regions for drought tolerance. These genes are more likely to be important for drought tolerance in an agricultural environment. To identify the metabolic processes with a significant G x E effect, we adapted the analysis software MapMan for rice. We found a drought stress induced shift toward senescence related degradation processes that was more pronounced in the sensitive than in the tolerant cultivars. In spite of higher growth rates and water use, more photosynthesis related genes were down-regulated in the tolerant than in the sensitive cultivars.     

Effects of chilling stress on leaf morphology,anatomy, ultrastructure,gas exchange,and essential oils in the seasonally dimorphic plant Teucrium polium (Lamiaceae)

The Mediterranean region (and globally also other regions) is characterized by the presence of phryganic plants, i.e. subshrubs that grow under hot and arid environmental conditions. These plants are reported to be affected by summer drought stress. However, in the present study the phryganic plant Teucrium polium (mountain germander) appears to be affected by winter chilling stress rather than by summer drought stress in a specific area. Winter leaves of the plant are smaller and thicker compared to summer leaves, have more stomata and glandular hairs, and their chloroplasts are larger, more numerous, with voluminous starch grains. Moreover, epidermal and mesophyll cells of winter leaves contain in their vacuoles dark phenolics and calcium oxalate crystals. Summer leaves are devoid of vacuolar phenolics and their chloroplasts possess many large plastoglobuli. Leaf gas exchange parameters (photosynthesis, transpiration, stomatal conductance) are significantly higher in winter leaves. Concentrations of osmoprotectors (stress indicators) like proline and soluble sugars are similarly higher in winter leaves. Essential oil assessments showed a significantly higher oil yield of winter leaves compared to summer leaves. Percentages of the major oil components (linalool, terpinen-4-ol, germacrene D, and spathulenol) are remarkably higher in winter oils than in summer oils. In conclusion, low environmental temperatures (1–10 °C) appear to decisively influence the structure and function of winter leaves compared to summer leaves. Winter plants undergo chilling stress to which they respond by developing various mechanical and chemical defensive strategies.