One dry summer: a leaf proteome study on the response of oak to drought exposure

One of the most prominent hallmarks of the expected climate change in Europe is the higher prevalence of longer and more intense periods of summer drought. To preserve European oak forests, of considerable importance for European economical and ecological development, under these conditions knowledge on the mechanisms by which broad-leaved trees cope with drought is needed. In this study the effect of one season of drought stress, corresponding in length and soil water content to a dry summer, on young pedunculate oak trees (Quercus robur L.) was investigated by monitoring phenotypical parameters, the analysis of carbohydrate accumulation and a 2D-DIGE-based proteome study of leaves. In our experimental system, mimicking the conditions of a dry summer, the plants displayed reduced growth, moreover the transition through the developmental stages was affected. The data obtained during this study, supported by a separately published gene expression analysis study, indicated that the oak tried to adapt its metabolism in order to maintain its full molecular functionality. Initially the plants seemed to be able to cope with the imposed stress. However prolonged drought exposure overwhelmed the adaptive mechanisms and at the last sampling point of this study the molecular machinery succumbed.     

Root growth of different oak provenances in two soils under drought stress and air warming conditions

Background and aims

Oaks are considered to be drought- and thermo-tolerant tree species. Nevertheless, species and provenances may differ in their ecological requirements. We hypothesised that (i) provenances from xeric sites are better adapted to drought than those from more humid sites, (ii) oaks direct root growth towards resource-rich layers, and (iii) air-warming promotes root growth.

Methods

To test different provenances of Quercus robur, Q. petraea and Q. pubescens, we conducted a model ecosystem experiment with young trees, grown on acidic and calcareous soil, subjected to drought, air warming, the combination of warming and drought, and a control.

Results

The results were only in partial agreement with the first hypothesis. As expected the provenances originating from drier sites produced more biomass than those from more humid sites under drought conditions. Surprisingly, however, they reacted more sensitive to water limiting conditions, as they produced also substantially more biomass under well-watered conditions. The drought treatment reduced root mass substantially in the upper soil. In agreement with the second hypothesis this led to a shift in the centre of root mass to lower depth, where water was still more available than closer to the soil surface. In contrast to the third hypothesis, the air-warming treatment, which was very mild however compared to climate change scenarios, had no significant effects on root growth.

Conclusions

Given that the provenances from drier sites showed more biomass loss at water limiting conditions than provenances from more humid sites, it remains questionable whether provenances from drier sites are better suited for a future climate.     

紫花苜蓿叶性状对干旱的阶段性响应

通过盆栽控水试验,研究了不同生育时期陇东苜蓿(Medicago sativa L.cv.Longdong)叶性状对不同程度干旱的响应。结果表明:(1)随干旱加重,叶干物质含量(LDMC)、叶氮含量(LN)、比叶重(LMA)、叶厚(LT)上升,叶面积(LA)减小,叶磷含量(LP)无明显变化,叶绿素含量(Chl)和叶长宽比(L/W)波动较大。(2)随生育时期的延长,LT、LDMC、L/W和LA变化不明显,LN下降,LP呈倒"V"型趋势,LMA和Chl波动较大。(3)L/W与LN、LT显著负相关;LDMC与LT、LMA显著正相关;LMA与LT、LN显著正相关,与L/W、LP显著负相关;LN与LT显著正相关;LA与LP显著正相关,与LDMC、LMA、LN显著负相关;Chl与其他叶性状均不相关。尽管干旱下陇东苜蓿不同生育时期叶性状响应并未表现出一致的变化,叶性状的差异性变化还是部分反映了陇东苜蓿适应干旱而采取的综合策略。从不同生育时期的差异性反应角度出发,探讨干旱下的叶性状响应是阐明优良牧草紫花苜蓿水分适应性的新的尝试。     

Airborne ethylene may alter antioxidant protection and reduce tolerance of holm oak to heat and drought stress

Plant-emitted ethylene has received considerable attention as a stress hormone and is considered to play a major role at low concentrations in the tolerance of several species to biotic and abiotic stresses. However, airborne ethylene at high concentrations, such as those found in polluted areas (20-100 nL L(-1)) for several days, has received far less attention in studies of plant stress tolerance, though it has been shown to alter photosynthesis and reproductive stages (seed germination, flowering, and fruit ripening) in some species. To assess the potential effects of airborne ethylene on plant stress tolerance in polluted areas, the extent of oxidative stress, photo- and antioxidant protection, and visual leaf area damage were evaluated in ethylene-treated (approximately 100 nL L(-1) in air) and control (without ethylene fumigation) holm oak (Quercus ilex) plants exposed to heat stress or to a combination of heat and drought stress. Control plants displayed tolerance to temperatures as high as 50 degrees C, which might be attributed, at least in part, to enhanced xanthophyll de-epoxidation and 2-fold increases in alpha-tocopherol, and they suffered oxidative stress only when water deficit was superimposed on temperatures above 45 degrees C. By contrast, ethylene-treated plants showed symptoms of oxidative stress at lower temperatures (35 degrees C) than the controls in drought, as indicated by enhanced malondialdehyde levels, lower alpha-tocopherol and ascorbate concentrations, and a shift of the redox state of ascorbate to its oxidized form. In addition, ethylene-treated plants showed higher visual leaf area damage and greater reductions in the maximum efficiency of the PSII photochemistry than controls in response to heat stress or to a combination of heat and drought stress. These results demonstrate for the first time that airborne ethylene at concentrations similar to those found in polluted areas may reduce plant stress tolerance by altering, among other possible mechanisms, antioxidant defenses.     

Soil respiration in a Mediterranean oak forest at different developmental stages after coppicing

To assess the variation of soil respiration at different forest stages we measured it in a coppiced oak (Quercus cerris L.) chronosequence in central Italy during two campaigns, spanning 2 successive years, in four stands at different stages of the rotation: 1 year (S1), 5 years (S5), 10 years (S10) and 17 years (S17) after coppicing. The contribution of the different components of soil respiration flux (aboveground litter, belowground decomposition soil organic matter and root respiration) was estimated by a paired comparison of manipulative experiments between the recently coppiced stand (S1) and mature stand (S17). Ninety percent of soil respiration values were between 1.7 and 7.8 μmol m^?2 s^?1, with an overall mean (±SD) of 4.0±2.7 μmol m^?2 s^?1. Spatial variation of soil respiration was high (CV=44.9%), with a mean range (i.e. patch size) of 4.8±2.7 m, as estimated from a semivariance analysis. In the absence of limitation by soil moisture, soil respiration was related to soil temperature with the exponential Q₁₀ model (average Q₁₀=2.25). During summer, soil moisture constrained soil respiration and masked its dependence on soil temperature. Soil respiration declined over the years after coppicing. Assuming a linear decline with stand age, we estimated a reduction of 24% over a 20‐year‐rotation cycle. The response of soil respiration to temperature also changed with age of the stands: the Q₁₀ was estimated to decrease from 2.90 in S1 to 2.42 in S17, suggesting that different components or processes may be involved at different developmental stages. The contribution of heterotrophic respiration to total soil respiration flux was relatively larger in the young S1 stand than in the mature S17 stand.     

春小麦不同发育阶段抗氧化系统对田间缓慢干旱的响应

研究了两种抗旱性不同的春小麦(Triticum aestivum L.)品种定西24(抗旱性较强)和品种8139(抗旱性较弱)不同发育阶段体内抗氧化系统对田间缓慢干旱的响应情况。结果表明,在田间自然干旱条件下,随着土壤水分含量的逐渐降低,两品种小麦叶片水势和含水量均缓慢降低,叶片色素及可溶性蛋白含量也于幼苗期显著降低,植株生长受抑。叶片抗氧化酶系统如SOD、：POD、CAT以及GSH—ASC循环中的两种关键酶APX和GR活性,均在小麦发育前期如幼苗期和拔节期显著升高而于后期下降。主要抗氧化物质ASC含量也表现出相似的变化趋势。虽然抗氧化系统在两春小麦品种不同发育阶段对田间干旱的响应行为大体相同,而且干旱较敏感品种8139各物质对干旱的响应强于干旱较耐受品种定西24,但后者减轻干旱导致的氧化损伤的效率高于前者。试验还表明,在作物的不同发育阶段,抗氧化系统对田间缓慢干旱响应的策略不同,前期如幼苗期和拔节期主要表现为积极应对,后期如抽穗期和灌浆期主要表现为被动忍耐。     

Effects of silicon on defense of wheat against oxidative stress under drought at different developmental stages

The effects of silicon application before sowing on the drought-induced oxidative stress and antioxidant defense in wheat (Triticum aestivum L.) were investigated. Drought stress was applied by withholding watering till sampling at booting or filling stage. Application of Si increased the water potential of drought-stressed plants at filling stage, whereas it did not at booting stage. The superoxide dismutase (SOD) activity was inhibited and peroxidase (POD) activity was enhanced by drought at booting stage, and no differences were observed due to the Si treatment. At filling stage, however, application of Si increased the SOD activity and decreased the POD activity of drought-stressed plants. The catalase (CAT) activity was slightly increased by drought only in the absence of Si and at booting stage. The activity of glutathione reductase (GR) was not greatly influenced. Application of Si did not change the contents of H₂O₂, total soluble protein and protein carbonyl of drought-stressed plants at booting stage, whereas at filling stage, it decreased the content of H₂O₂ and protein carbonyl and increased the content of total soluble protein. The content of thiobarbituric acid reactive substances (TBARS) and the activities of acid phospholipase (AP) and lipoxygenase (LOX) in drought-stressed plants were also decreased by application of Si at both stages.     

Changes in the tobacco leaf apoplast proteome in response to salt stress

The apoplast of plant cells is a dynamic compartment involved in many processes, including maintenance of tissue shape, development, nutrition, signalling, detoxification and defence. In this work we used Nicotiana tabacum plants as a model to investigate changes in the soluble apoplast composition induced in response to salt stress. Apoplastic fluid was extracted from leaves of control plants and plants exposed to salt stress, using a vacuum infiltration procedure. Two-dimension electrophoretic analyses revealed about 150 polypeptide spots in the pH range of 3.0 to 10.0, in independent protein extracts, with a high level of reproducibility between the two sample sets. Quantitative evaluation and statistical analyses of the resolved spots in treated and untreated samples revealed 20 polypeptides whose abundance changed in response to salt stress. Mass spectroscopic peptide separation and sequencing was used to identify polypeptides affected by salt stress. While the levels of some proteins were reduced by salt-treatment, an enhanced accumulation of protein species known to be induced by biotic and abiotic stresses was observed. In particular, two chitinases and a germin-like protein increased significantly and two lipid transfer proteins were expressed entirely de novo. Some apoplastic polypeptides, involved in cell wall modifications during plant development, remained largely unchanged. The significance of these components is discussed in the context of stress responses in plants.     

Variation in the genetic structure and reproductive biology of holm oak populations

Five polymorphic enzymatic loci were studied in 30 populations of Quercus ilex distributed from Crete to North Africa. A high within-population genetic diversity was found for each locus studied. Most of the alleles were common to all the populations, indicating that the holm oak corresponds to a single genetic entity. Observation of breeding system characteristics showed that the holm oak is monoecious, wind-pollinated, and likely to possess genetic autoincompatibility. Furthermore, studies of flowering phenology in a single population showed that the period of flowering varied notably among trees. An average of 29% of the trees showed inter-annual variation in flowering time. The male, female or vegetative investment also varied widely among trees from one year to another. This results in a diversification of pollen source received by a given tree each year, and also from one year to another.     

干旱胁迫对不同种源香椿叶片膜脂过氧化和保护酶系统的影响

对来源于江苏、四川、湖南、湖北、河南和陕西的香椿〔Toona sinensis(A.Juss.)Roem.〕苗进行盆栽实验,研究干旱胁迫对香椿叶片膜脂过氧化和保护酶系统的影响。结果表明,随干旱胁迫程度的加强,6个种源香椿苗叶片中的丙二醛(MDA)含量增加,超氧化物歧化酶(SOD)和过氧化物酶(POD)活性增强,但各指标的变化幅度因种源不同而异。复水后,除重度干旱胁迫造成的SOD活性变化难以恢复外,其余指标基本能恢复至对照水平。综合MDA含量及SOD和POD活性的变化情况认为,来源于河南、陕西和江苏的香椿具有较强的抗旱能力,而来源于湖北、四川和湖南的香椿抗旱能力较弱。     

Changes of dehydrin profiles induced by drought in winter wheat at different developmental stages

Two cultivars of winter wheat (Triticum aestivum L.) differing in their drought tolerance (KTC86211 and ND7532) were subjected to a progressive soil water stress and recovery at four developmental stages. Dehydrins with molecular masses of 45 and 37 kDa were constitutively accumulated during all stages in both genotypes. The 28 kDa dehydrin accumulated exclusively at seedling stage in both genotypes. The 49 and 40 kDa dehydrins accumulated at both tillering and jointing stages but showed a genotype-specific pattern. The content of most dehydrins increased with decreased soil moisture and then decreased during recovery. These results suggest that accumulation pattern of dehydrins during water stress was related to the genotype and developmental stage.     

Variation in the intestinal microbiota at different developmental stages of Hynobius maoershanensis

Intestinal microbiota play an important role in the life of amphibians and its composition may vary by developmental stage. In this study, 16S rRNA high‐throughput sequencing was used to profile the intestinal microbiota of Hynobius maoershanensis, which exclusively inhabit the Maoer Mountain swamp at an altitude of approximately 2,000 m. We characterized the bacterial composition, structure, and function of the microbiota of H. maoershanensis at different developmental stages. The alpha diversity was not markedly different for the Simpson, Shannon, Ace, and Sobs indices of microbes. The beta diversity revealed that there were age‐related differences in the structure of the intestinal microbes of H. maoershanensis, specifically, at the phylum level. Bacteroidetes and Proteobacteria were the dominant bacteria present in the adult stage, and the relative abundance of Bacteroidetes was significantly higher compared with that of tadpoles. Firmicutes and Proteobacteria were the dominant phylum during the tadpole stage and their relative abundance was significantly higher compared with the adult period. Functional analysis revealed that the pathways associated with organismal systems and metabolism were significantly enriched in the adults, whereas human diseases, genetic information processing, and cellular processes were more enriched in the hindlimb bud stage. Human diseases and environmental information processing were more enriched in the forelimb bud stage at KEGG pathway level 1. Possibilities for the observed discrepancies include the adaptation to eating habits and the remodeling of the intestines during development. We speculated that H. maoershanensis adults may be more suitable to a high‐fiber diet, whereas the tadpoles are associated with a carnivorous diet. Our study provides evidence of variations in the intestinal microbiota during development in amphibians, highlighting the influence of historical developments on the intestinal microbiota and an increased understanding of the importance of physiological characteristics in shaping the intestinal microbiota of amphibians. These data will help us formulate more effective protection measures for H. maoershanensis.     

茂兰喀斯特森林不同演替阶段植物叶片功能性状与土壤因子的关系

植物如何改变功能性状来适应环境一直是生态学的研究征点。为探究茂兰喀斯特森林不同演替阶段植物叶片的适应策略，该文以茂兰自然保护区5个不同演替阶段(草本、灌木、灌乔、乔木和顶极群落阶段)优势种为研究对象，测定不同演替阶段的优势植物叶片功能性状与土壤理化性质。结果表明：(1)随着植被正向演替的进行，土壤全氮(STN)含量、土壤有机质(SOM)含量、土壤含水量(SWC)逐渐增加，土壤全磷(STP)含量和土壤全钾(STK)含量先增加后减少，土壤pH值整体呈减小的趋势。(2)随着植被演替的进行，叶面积(LA)、叶干物质含量(LDMC)、叶厚度(LT)和叶片碳含量(LCC)逐渐上升，比叶面积(SLA)与叶片钾含量(LKC)则与之相反，叶片氮含量(LNC)呈先升后降的趋势，叶片磷含量(LPC)呈先降后升的趋势。(3)冗余分析表明，演替初期植物主要分布在土壤pH值高而STK、STP、SWC、SOM、STN相对低的环境中，群落内植物叶片采取高SLA、LNC、LPC,低LA、LDMC、LT、LWC的性状组合，演替晚期植物主要分布在土壤水分和养分含量较高的环境，LDMC、LT、LA、LWC与演替初期相比呈上升...     

不同生育时期干旱对冬小麦氮素吸收与利用的影响

以抗旱性强的‘石家庄8号’和抗旱性弱的‘偃麦20’冬小麦(Triticum aestivum)为材料, 在田间遮雨棚条件下, 研究返青-拔节期、拔节-开花期和灌浆后期3个生育期不同干旱程度对冬小麦产量、氮素吸收、分配和利用的影响。结果表明, 在干旱条件下, 抗旱性强的‘石家庄8号’产量高于抗旱性弱的‘偃麦20’, 并且其3个生育时期轻度干旱均可提高产量。拔节-开花期干旱对两个冬小麦品种氮素的吸收和运转影响均最大, 其次为返青-拔节期, 而灌浆后期影响较小。不同生育期中度和重度干旱均降低了花前贮藏氮素向籽粒中的转移, 并且氮肥利用效率和生产率也较低, 而在返青-拔节和灌浆后期轻度干旱有利于营养器官的氮素向籽粒中转移, 提高了氮肥利用效率和生产率。在干旱条件下, 抗旱性强的‘石家庄8号’籽粒氮素积累对花前贮藏氮素再运转的依赖程度高, 而‘偃麦20’对花后氮素的积累和转移依赖较高。综合产量和氮素的转移特点, 在生产实践中, 返青-拔节期和灌浆后期要注意对小麦进行适度的干旱处理, 在拔节-开花期要保证冬小麦的充分灌溉, 从而有利于氮素的积累和分配。     

Comparative proteomic study reveals dynamic proteome changes between superhybrid rice LYP9 and its parents at different developmental stages

Heterosis is a common phenomenon in which the hybrids exhibit superior agronomic performance than either inbred parental lines. Although hybrid rice is one of the most successful apotheoses in crops utilizing heterosis, the molecular mechanisms underlying rice heterosis remain elusive. To gain a better understanding of the molecular mechanisms of rice heterosis, comparative leaf proteomic analysis between a superhybrid rice LYP9 and its parental cultivars 9311 and PA64s at tillering, flowering and grain-filling stages were carried out. A total of 384 differentially expressed proteins (DP) were detected and 297 DP were identified, corresponding to 222 unique proteins. As DP were divided into those between the parents (DP_PP) and between the hybrid and its parents (DP_HP), the comparative results demonstrate that proteins in the categories of photosynthesis, glycolysis, and disease/defense were mainly enriched in DP. Moreover, the number of identified DP_HP involved in photosynthesis, glycolysis, and disease/defense increased at flowering and grain-filling stages as compared to that at the tillering stage. Most of the up-regulated DP_HP involved in the three categories showed greater expression in LYP9 at flowering and grain-filling stages than at the tillering stage. In addition, CO₂ assimilation rate and apparent quantum yield of photosynthesis also showed a greater increase in LYP9 at flowering and grain-filling stages than at the tillering stage. These results suggest that the proteins involved in photosynthesis, glycolysis, and disease/defense as well as their dynamic regulation at different developmental stages may be responsible for heterosis in rice.     

Thylakoid proteome variation of Eutrema salsugineum in response to drought and salinity combined stress

It is well known that plant responses to stress involve different events occurring at different places of the cell/leaf and at different time scales in relation with the plant development. In fact, the organelles proteomes include a wide range of proteins that could include a wide range of proteins showing a considerable change in cellular functions and metabolism process. On this basis, a comparative proteomics analysis and fluorescence induction measurements were performed to investigate the photosynthetic performance and the relative thylakoid proteome variation in Eutrema salsugineum cultivated under salt stress (200 mM NaCl), water deficit stress (PEG) and combined treatment (PEG + NaCl) as a hyperosmotic stress. The obtained results showed a significant decrease of plant growth under drought stress conditions, with the appearance of some toxicity symptoms, especially in plants subjected to combined treatment. Application of salt or water stress alone showed no apparent change in the chlorophyll a fluorescence transients, primary photochemistry (fluorescence kinetics of the O-J phase), the PQ pool state (J-I phase changes), (Fv/Fm) and (Fk/Fj) ratios. However, a considerable decrease of all these parameters was observed under severe osmotic stress (PEG + NaCl). The thylakoid proteome analysis revealed 58 proteins showing a significant variation in their abundance between treatments (up or down regulation). The combined treatment (PEG + NaCl) induced a decrease in the expression of the whole PSII core subunit (D1, D2, CP43, CP47, PsbE and PsbH), whereas the OEC subunits proteins remained constant. An increase in the amount of PsaD, PsaE, PsaF, PsaH, PsaK and PsaN was detected under drought stress (PEG5%). No significant change in the accumulation of Cyt b6 and Cyt f was observed. Some regulated proteins involved in cellular redox homeostasis were detected (glutamine synthetase, phosphoglycerate kinase, transketolase), and showed a significant decrease under the combined treatment. Some oxidative stress related proteins were significantly up-regulated under salt or drought stress and could play a crucial role in the PSI photoprotection and the control of ROS production level.     

Photosynthetic response of sweet sorghum to drought and re‐watering at different growth stages

Sweet sorghum (Sorghum bicolor) is a C4 drought resistant species with a huge potential for bioenergy. Accentuated reductions in water availability for crop production and altered rainfall distribution patterns, however, will have direct impact on its physiological attributes, metabolic functions and plant growth. The objective of this study was to evaluate the effects of drought and re‐watering on the photosynthetic efficiency of sweet sorghum. Durable or short transient drought stress periods were imposed at early and late growth stages and compared with well‐watered plants. In spite of very similar drought levels at early and late growth stages (Ψ_soil = ?1.6 and ?1.7 MPa), the decrements in maximum quantum yield (?_Po) and performance index (PI) were about twice at late than at early growth stages. All the PI components, that is, density of active reaction centers (RCs), excitation energy trapping and conversion of excitation energy into electron flow followed a similar decreasing pattern. Upon re‐watering and regardless the duration and growth stage of the drought period, all the photosynthetic functions, and particularly those of photosystem II (PSII), fully recovered. Such effective self‐regulating functional activity by PSII photochemistry likely contributes to both high drought resistance and photosynthetic recovery capacity of sweet sorghum. At vegetative growth stages, the down regulation of the photochemistry seems to be the main photoprotective/regulative mechanisms, while at late growth stages, the accumulation of compatible solutes likely has a more preponderant role. The observed sugar concentration increments likely contributed to prevent permanent photo‐oxidative destruction of the PSII RCs of mature droughted sweet sorghum plants.