盐胁迫下荒漠共生植物红砂与珍珠的根茎叶中离子吸收与分配特征

西北荒漠地区C3小灌木红砂(Reaumuria soongorica)和C4半灌木珍珠猪毛菜(Salsola passerina)在特定环境下混生在一起,分布面积广阔。以采自腾格里沙漠边缘荒漠地带的天然野生珍珠猪毛菜和红砂群落的幼苗为材料,经0、100、200、300、400mmol/L NaCl盐溶液共同胁迫10 d,检测它们的含水量、主要矿质离子在根茎叶的含量与分布,揭示二者耐盐的共生协同的离子平衡适应机制。试验结果发现,珍珠猪毛菜叶片具有"吸钾排钠的"的耐盐特征,红砂叶片具备"吸钠排钾"的特征,吸收利用无机矿质离子具备互补效应。二者耐盐Cl、Ca和Si离子吸收与累积能力存在很大差异:随着盐胁迫程度加剧,红砂的根茎叶中Cl离子含量持续增加,并且为珍珠猪毛菜的2—5倍;珍珠猪毛菜根中Ca离子含量为红砂的2—3倍,但含量变化不显著;红砂根中Si离子含量迅速降低后稳定,并且是珍珠猪毛菜根的3—5倍,其他器官变化差异较小。因此,红砂与珍珠猪毛菜的共培养盐胁迫下根中吸收的离子侧重不同,红砂以Na、Cl、Si为主,珍珠猪毛菜以K、Ca为主。随着盐胁迫的程度加强,离子选择吸收系数S k,Na的变化趋势降低,表明二者叶部对Na的选择性减小,K的选择性吸收积累增大,增强了它们的抗盐性,最终使叶片所受盐害减小。总之红砂与珍珠猪毛菜共生的耐盐离子稳态机制显著不同,离子吸收与分布具有互补互利的效应。     

The photosynthetic pathway of the roots of twelve epiphytic orchids with CAM leaves

The photosynthetic pathway of the roots (both the white velamentous main portions and the green, nonvelamentous tips) was investigated in twelve taxa (natural species and intergeneric hybrid cultivars) of epiphytic orchids having CAM leaves. All organs contained chlorophyll, and the a/b ratios indicate that the organs, especially the roots, are likely shade-adapted. Stable carbon isotope ratios of the tissues were near −15‰ for all organs, a value typical of obligate (constitutive) CAM plants. Values for root tissues were slightly lower (more negative) than those of the leaves. The presence of CAM in the leaves of these orchids did not ensure that their roots performed CAM photosynthesis. Further work is needed to address the questions raised in this study and to determine if the photosynthetic roots of these taxa are capable of assimilating atmospheric CO₂.     

巨桉根系分解对菊苣生长及光合特性的影响

巨桉是我国退耕还林过程中采用的重要速生树种之一,被广泛用于人工造林。采用盆栽试验,研究了巨桉根系分解初期对菊苣幼苗生长和光合生理特性的影响。试验设置A1(50 g/盆)、A2(100 g/盆)和对照(CK)3个根系水平,将各处理的根系分别与10 kg土壤混合后装盆,播种菊苣。待A2处理植株的第3片真叶完全展开后测定菊苣光合生理指标及相关生长指标。结果表明:在巨桉根系分解初期,明显抑制了菊苣高生长、根生长、生物量积累、叶面积扩展及光合色素的合成,且随着根系添加量的增加抑制作用加大;菊苣叶片胞间CO2浓度(Ci)增加,而净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)均显著低于对照;随土壤中根系含量的增加,除CO2补偿点(CCP)呈增加趋势外,其他光响应和CO2响应的特征参数均呈明显的下降趋势,并与对照差异显著;各生长指标除与胞间CO2浓度呈现出负相关外,与其它光合特征参数、光合色素以及相应的响应曲线参数之间均呈现出显著或极显著的正相关关系;通过GC-MS检测表明,巨桉根系中含有2,6-二叔丁基对甲酚、N-甲基苯乙胺等多种具有化感潜力化学物质,在其分解过程中,这些化感物质逐步释放并作用于受体植物,抑制其光合色素合成和光合作用,降低其环境适应能力,从而抑制菊苣的生长。     

Variable Photosynthetic Metabolism in Leaves and Stems of Cissus quadrangularis L

By measuring titratable acidity, gas exchange parameters, mesophyll succulence, and ¹³C/¹²C ratios, we have shown that Cissus quadrangularis L. has C₃-like leaves and stems with Crassulacean acid metabolism (CAM). In addition, the nonsucculent leaves show the diurnal fluctuations in organic acids termed recycling despite the fact that all CO₂ uptake and stomatal opening occurs during the day. Young succulent stems have more C₃ photosynthesis than older stems, but both have characteristics of CAM. The genus Cissus will be a fruitful group to study the physiology, ecology, and evolution of C₃ and CAM since species occur that exhibit characteristics of both photosynthetic pathways.     

Spatial patterns of photosynthesis in thin- and thick-leaved epiphytic orchids: unravelling C3–CAM plasticity in an organ-compartmented way

Background and Aims

A positive correlation between tissue thickness and crassulacean acid metabolism (CAM) expression has been frequently suggested. Therefore, this study addressed the question of whether water availability modulates photosynthetic plasticity in different organs of two epiphytic orchids with distinct leaf thickness.

Methods

Tissue morphology and photosynthetic mode (C₃ and/or CAM) were examined in leaves, pseudobulbs and roots of a thick-leaved (Cattleya walkeriana) and a thin-leaved (Oncidium ‘Aloha’) epiphytic orchid. Morphological features were studied comparing the drought-induced physiological responses observed in each organ after 30 d of either drought or well-watered treatments.

Key Results

Cattleya walkeriana, which is considered a constitutive CAM orchid, displayed a clear drought-induced up-regulation of CAM in its thick leaves but not in its non-leaf organs (pseudobulbs and roots). The set of morphological traits of Cattleya leaves suggested the drought-inducible CAM up-regulation as a possible mechanism of increasing water-use efficiency and carbon economy. Conversely, although belonging to an orchid genus classically considered as performing C₃ photosynthesis, Oncidium ‘Aloha’ under drought seemed to express facultative CAM in its roots and pseudobulbs but not in its leaves, indicating that such photosynthetic responses might compensate for the lack of capacity to perform CAM in its thin leaves. Morphological features of Oncidium leaves also indicated lower efficiency in preventing water and CO₂ losses, while aerenchyma ducts connecting pseudobulbs and leaves suggested a compartmentalized mechanism of nighttime carboxylation via phosphoenolpyruvate carboxylase (PEPC) (pseudobulbs) and daytime carboxylation via Rubisco (leaves) in drought-exposed Oncidium plants.

Conclusions

Water availability modulated CAM expression in an organ-compartmented manner in both orchids studied. As distinct regions of the same orchid could perform different photosynthetic pathways and variable degrees of CAM expression depending on the water availability, more attention should be addressed to this in future studies concerning the abundance of CAM plants.     

Carbon and Nitrogen Metabolism in Leaves and Roots of Dwarf Bamboo (Fargesia denudata Yi) Subjected to Drought for Two Consecutive Years During Sprouting Period

Dwarf bamboo is an ecologically and economically important forest resource that is widespread in mountainous regions of eastern Asia and southern America. Fargesia denudata, one of the most important dwarf bamboos, is a staple food of the giant panda, but our knowledge about how F. denudata copes with drought stress is very limited. The objective of this study was to determine the responses of carbon (C) and nitrogen (N) metabolism to drought in leaves and roots of F. denudata plants. Plants were subjected to three water treatments, well-watered [WW, 85 % relative soil water content (RSWC)], moderate drought (MD, 50 % RSWC), and severe drought (SD, 30 % RSWC), for two consecutive years during the sprouting period. Plant growth parameters, levels of carbohydrates and N compounds, and activities of key enzymes involved in C and N metabolism were analyzed. In young leaves, C metabolism was in balance after drought stress, but nitrate (NO₃ ^?) reduction and ammonium (NH₄ ⁺) assimilation were accelerated. In old leaves, drought stress decreased carbohydrate contents by spurring the activities of the main enzymes that participate in C metabolism, whereas N metabolism was enhanced only under SD. Roots showed unchanged C metabolism parameters under MD, together with stable NO₃ ^? reduction and the key enzymes related to NH₄ ⁺ assimilation, whereas they were stimulated by SD. Hydrolysates of carbohydrates in old leaves could be transferred into roots, but only to meet MD. Meanwhile, roots could allocate more N nutrition to young leaves and less to old leaves. These changes regulated the overall metabolic balance of F. denudata. Consequently, the results indicate that different organs with various response strategies will be well adapted to different drought intensities for ensuring regular growth of F. denudata plants at the whole-plant level.     

Measuring whole plant CO2 exchange with the environment reveals opposing effects of the gin2–1 mutation in shoots and roots of Arabidopsis thaliana

Using a cuvette for simultaneous measurement of net photosynthesis in above ground plant organs and root respiration we investigated the effect of reduced leaf glucokinase activity on plant carbon balance. The gin2–1 mutant of Arabidopsis thaliana is characterized by a 50% reduction of glucokinase activity in the shoot, while activity in roots is about fivefold higher and similar to wild type plants. High levels of sucrose accumulating in leaves during the light period correlated with elevated root respiration in gin2–1. Despite substantial respiratory losses in roots, growth retardation was moderate, probably because photosynthetic carbon fixation was simultaneously elevated in gin2–1. Our data indicate that futile cycling of sucrose in shoots exerts a reduction on net CO₂ gain, but this is over-compensated by the prevention of exaggerated root respiration resulting from high sucrose concentration in leaf tissue.     

Spatial division of phosphoenolpyruvate carboxylase and nitrate reductase activity and its regulation by cytokinins in CAM-induced leaves of Guzmania monostachia (Bromeliaceae)

Crassulacean acid metabolism (CAM) is a physiological adaptation of plants that live in stress environment conditions. A good model of CAM modulation is the epiphytic bromeliad, Guzmania monostachia, which switches between two photosynthetic pathways (C₃–CAM) in response to different environmental conditions, such as light stress and water availability. Along the leaf length a gradient of acidity can be observed when G. monostachia plants are kept under water deficiency. Previous studies showed that the apical portions of the leaves present higher expression of CAM, while the basal regions exhibit lower expression of this photosynthetic pathway. The present study has demonstrated that it is possible to induce the CAM pathway in detached leaves of G. monostachia kept under water deficit for 7 d. Also, it was evaluated whether CAM expression can be modulated in detached leaves of Guzmania and whether some spatial separation between NO₃⁻ reduction and CO₂ fixation occurs in basal and apical portions of the leaf. In addition, we analyzed the involvement of endogenous cytokinins (free and ribosylated forms) as possible signal modulating both NO₃⁻ reduction and CO₂ fixation along the leaf blade of this bromeliad. Besides demonstrating a clear spatial and functional separation of carbon and nitrogen metabolism along G. monostachia leaves, the results obtained also indicated a probable negative correlation between endogenous free cytokinins – zeatin (Z) and isopentenyladenine (iP) – concentration and PEPC activity in the apical portions of G. monostachia leaves kept under water deficit. On the other hand, a possible positive correlation between endogenous Z and iP levels and NR activity in basal portions of drought-exposed and control leaves was verified. Together with the observations presented above, results obtained with exogenous cytokinins treatments, strongly suggest that free cytokinins might act as a stimulatory signal involved in NR activity regulation and as a negative regulator of PEPC activity in CAM-induced leaves of G. monostachia during a diel cycle.     

Physiological responses of Plantago algarbiensis and P. almogravensis shoots and plantlets to low pH and aluminum stress

We investigated the impact of low pH and aluminum (Al) stress on the growth, nutrients concentration, chlorophyll a fluorescence, photosynthetic pigment contents, proline and carbohydrate accumulation in shoots and plantlets (leaves and roots) of Plantago almogravensis and P. algarbiensis. Both species accumulated considerable and similar amounts of Al in their tissues, mainly in the roots. The presence of Al caused a significant reduction on root elongation in P. algarbiensis. Low pH and Al induced significant changes on nutrient accumulation, but no significant alterations on the maximum efficiency of PSII (F _v/F _m), quantum yield of PSII photochemistry (?_PSII), quantum yield of regulated energy dissipation (?_NPQ) and quantum yield of non-regulated energy dissipation (?_NO) were detected in both species in response to these stresses. However, Al increased significantly the non-photochemical quenching and the chlorophyll b content and decreased the PSII excitation pressure (1 ? q _p) in P. almogravensis leaves. Both stress treatments induced carbohydrate accumulation in the shoots and roots of this species, but not in leaves. In P. algarbiensis, low pH and Al decreased the photosynthetic pigment contents in the shoots, whereas Al stimulated the carbohydrate accumulation in the leaves. Although our data showed that both species are tolerant to Al³⁺ and H⁺, P. almogravensis appeared to be more adapted to maintain cellular physiology and growth under those conditions.     

Plasticity in carbon acquisition of the heterophyllous Luronium natans: An endangered freshwater species in Europe

Luronium natans (L.) Raf. (Floating Water-plantain) is an endangered amphibious freshwater species endemic to Europe. We examined the plasticity in carbon acquisition and photosynthesis in L. natans to assess if lack of plasticity could contribute to explain the low competitive ability of the species. The plasticity of photosynthesis in submerged leaves towards inorganic carbon availability was examined and the photosynthesis of submerged, floating and aerial leaves was contrasted. L. natans was shown to be plastic in inorganic carbon uptake, as it was able to effectively acclimate to changed concentrations of free-CO₂. The photosynthetic apparatus was down-regulated in plants grown at high CO₂. Chlorophyll concentration, Rubisco activity and maximum photosynthesis were significantly lower in submerged leaves of plants grown at high CO₂ (200 μM free-CO₂) compared to plants grown at low CO₂ (18 μM free-CO₂). Furthermore, bicarbonate utilization was down-regulated in response to high CO₂. Carbon acquisition of submerged, floating and aerial leaves of L. natans differed significantly. The aerial leaves were superior in photosynthesising in air and, surprisingly, the floating leaves had the highest rates of photosynthesis in water. The study did not support the hypothesis that the low competitive ability of L. natans is caused by inefficient photosynthesis or a lack of plasticity in photosynthesis. However, the somewhat low photosynthetic performance of the submerged leaves may be a contributing factor.     

Arbuscular Mycorrhizal Symbiosis with Arundo donax Decreases Root Respiration and Increases Both Photosynthesis and Plant Biomass Accumulation

The effect of arbuscular mycorrhiza (AM) symbiosis on plant growth is associated with the balance between costs and benefits. A feedback regulation loop has been described in which the higher carbohydrate cost to plants for AM symbiosis is compensated by increases in their photosynthetic rates. Nevertheless, plant carbon balance depends both on photosynthetic carbon uptake and respiratory carbon consumption. The hypothesis behind this research was that the role of respiration in plant growth under AM symbiosis may be as important as that of photosynthesis. This hypothesis was tested in Arundo donax L. plantlets inoculated with Rhizophagus irregularis and Funneliformis mosseae. We tested the effects of AM inoculation on both photosynthetic capacity and in vivo leaf and root respiration. Additionally, analyses of the primary metabolism and ion content were performed in both leaves and roots. AM inoculation increased photosynthesis through increased CO₂ diffusion and electron transport in the chloroplast. Moreover, respiration decreased only in AM roots via the cytochrome oxidase pathway (COP) as measured by the oxygen isotope technique. This decline in the COP can be related to the reduced respiratory metabolism and substrates (sugars and tricarboxylic acid cycle intermediates) observed in roots.     

Hydroxytropane tiglates in the roots of Mandragora species

Roots of Mandragora autumnalis and M. vernalis contain hyoscyamine, hyoscine, cuscohygrine, apoatropine 3α-tigloyloxytropane and 3,6-ditigloyloxytropane. Belladonnine is present in the dried roots but could not be detected in fresh roots. No major differences were found in the alkaloids present in the two species. This is the first time the presence of tiglic acid esters has been reported in Mandragora species and the significance of this in the chemotaxonomy of the genus is indicated.     

黄土丘陵区油松人工林生态系统碳密度及其分配

以子午岭林区油松(Pinus tabulaeformis)人工林为研究对象,通过野外调查与室内分析,探讨了幼龄9a、中龄23a、近熟33a和成熟47a等不同林龄林分的生物量、含碳率、碳密度及其时空分布特征。结果表明:(1)油松林各群落平均生物量大小排序为:乔木层(76.12 t/hm2)枯落物层(14.56 t/hm2)林下植被层(3.66 t/hm2)。乔木层生物量随林龄增大而持续增加,各器官中树干所占比例最大(38%—46%),其次为叶和根,枝和皮所占比例最小;林下植被层生物量随林龄增大呈先降低后增加趋势;枯落物层生物量随林龄增大则明显增加。(2)油松乔木、林下灌木、草本、枯落物平均含碳率依次为50.2%、44.5%、43.8%和40.6%。林龄对乔木各器官含碳率无显著影响,不同器官之间含碳率存在显著性差异,具体表现为叶(53.3%)枝(51.4%)皮(50.6%)干(49.8%)根(47.3%);灌木各器官含碳率表现为枝(46.0%)叶(44.8%)根(42.5%),草本则是地上(45.2%)地下(40.2%)。土壤(0—100 cm)含碳率在0.3%—2.7%之间,且具有明显的垂直分布特征:表层含碳率高,并随土壤深度的增加逐渐降低。(3)9、23、33和47年生油松林生态系统碳密度分别为70.49、100.48、167.71和144.26 t/hm2,其空间分布序列表现为土壤层植被层枯落物层,且植被层和土壤层是油松人工林的主要碳库。林龄是影响油松林木及群落碳密度积累的主导因子之一。随林龄增加,土壤碳密度所占生态系统碳密度份额逐渐降低,乔木层和枯落物层则逐渐增加。     

CAM photosynthesis in submerged aquatic plants

Crassulacean acid metabolism (CAM) is a CO₂-concentrating mechanism selected in response to aridity in terrestrial habitats, and, in aquatic environments, to ambient limitations of carbon. Evidence is reviewed for its presence in five genera of aquatic vascular plants, includingIsoëtes, Sagittaria, Vallisneria, Crassula, andLittorella. Initially, aquatic CAM was considered by some to be an oxymoron, but some aquatic species have been studied in sufficient detail to say definitively that they possess CAM photosynthesis. CO₂-concentrating mechanisms in photosynthetic organs require a barrier to leakage; e.g., terrestrial C₄ plants have suberized bundle sheath cells and terrestrial CAM plants high stomatal resistance. In aquatic CAM plants the primary barrier to CO₂ leakage is the extremely high difrusional resistance of water. This, coupled with the sink provided by extensive intercellular gas space, generates daytime CO₂(pi) comparable to terrestrial CAM plants. CAM contributes to the carbon budget by both net carbon gain and carbon recycling, and the magnitude of each is environmentally influenced. Aquatic CAM plants inhabit sites where photosynthesis is potentially limited by carbon. Many occupy moderately fertile shallow temporary pools that experience extreme diel fluctuations in carbon availability. CAM plants are able to take advantage of elevated nighttime CO2 levels in these habitats. This gives them a competitive advantage over non-CAM species that are carbon starved during the day and an advantage over species that expend energy in membrane transport of bicarbonate. Some aquatic CAM plants are distributed in highly infertile lakes, where extreme carbon limitation and light are important selective factors. Compilation of reports on diel changes in titratable acidity and malate show 69 out of 180 species have significant overnight accumulation, although evidence is presented discounting CAM in some. It is concluded that similar proportions of the aquatic and terrestrial floras have evolved CAM photosynthesis. AquaticIsoëtes (Lycophyta) represent the oldest lineage of CAM plants and cladistic analysis supports an origin for CAM in seasonal wetlands, from which it has radiated into oligotrophic lakes and into terrestrial habitats. Temperate Zone terrestrial species share many characteristics with amphibious ancestors, which in their temporary terrestrial stage, produce functional stomata and switch from CAM to C₃. Many lacustrineIsoëtes have retained the phenotypic plasticity of amphibious species and can adapt to an aerial environment by development of stomata and switching to C₃. However, in some neotropical alpine species, adaptations to the lacustrine environment are genetically fixed and these constitutive species fail to produce stomata or loose CAM when artificially maintained in an aerial environment. It is hypothesized that neotropical lacustrine species may be more ancient in origin and have given rise to terrestrial species, which have retained most of the characteristics of their aquatic ancestry, including astomatous leaves, CAM and sediment-based carbon nutrition.     

Positive effects of night warming on physiology of coniferous trees in late growing season: Leaf and root

Previous studies about the effects of experimental warming on tree species have focused primarily on response of morphology and physiology in leaf and biomass allocation in the growing season, and a few studies considered the importance of roots. Based on the available evidence, it is unclear whether photosynthesis rate is enhanced by night warming in late autumn an issue that deserves further investigation. Thus, we exposed two coniferous species, Picea asperata and Abies faxoniana, to night warming continued throughout the year to investigate morphological and physiological responses of roots and leaves in the autumn. The results showed that night warming caused significant increases in net influxes of NH₄⁺ and NO₃⁻ in P. asperata seedlings corresponding well with net H⁺ efflux and net influx of O₂. Meanwhile, night warming had a positive effect on foliar gas exchange such as net photosynthesis rate, apparent quantum efficiency, dark respiration rate and maximum quantum efficiency of PS II, and nitrate reductase activity of roots. Additionally, root morphology such as total roots length, surface area, specific root area and specific root length was also stimulated by night warming. In contrast, night warming decreased concentrations of non-structural carbohydrate in leaves and roots of both species in autumn. The present study demonstrates that night warming would enhance late autumn leaf photosynthetic rate, and increase N uptake capacity of roots.     

The role of root nitrate reduction in the systemic control of biomass partitioning between leaves and roots in accordance to the C/N-status of tobacco plants

The root/shoot-ratio is a simple parameter to describe the systemic response of plants to alterations of their nutritional status, as indicated by the C/N-balance of leaves. The ‘functional equilibrium hypothesis’ holds that leaf growth is limited by the supply of nitrogen from the roots, whereas root growth depends on the carbon supply from leaves. The nature of the systemic control that balances root and shoot growth is not fully understood. Previous experiments have shown that root growth of transformed tobacco plants, which lack functional root nitrate reductase, was severely impeded, when plants were grown on NO ₃ ^? as the sole N-source. In these experiments, the root/shoot-ratio was correlated with the Glutamate/Glutamine-ratio of roots. In the present study we tested the hypothesis that high internal Glu contents (in relation to Gln) inhibit root growth. Wild type and transformed tobacco plants were given access to both NH₄ and NO₃, and were cultivated at ambient and elevated pCO₂ in order to vary carbon availability. The uptake and assimilation of NH ₄ ⁺ by the root was significantly higher in transformed than in wild type tobacco, in particular at elevated pCO₂. Consequently, the Glu/Gln-ratio in the root of transformants was significantly lower than in NO ₃ ^? -grown plants, and was, in the present study, not different from the wild type. However, we failed to observe a correlation between plant architecture and the Glu/Gln-ratio of roots, suggesting that signals arising from the immediate products of nitrate reduction (nitrite) are involved in the systemic control of root growth. Furthermore the synthesis of root-derived signals, which affect N-turnover, starch re-mobilization and the growth of leaves, appears to be associated with root nitrate reduction. This enzymatic step seems to be indispensable for the systemic control of biomass partitioning, and plays a crucial role for the integration of carbon and nitrogen metabolism at the whole plant level.     

Proteomic analysis of Citrus sinensis roots and leaves in response to long-term magnesium-deficiency

Background

Magnesium (Mg)-deficiency is frequently observed in Citrus plantations and is responsible for the loss of productivity and poor fruit quality. Knowledge on the effects of Mg-deficiency on upstream targets is scarce. Seedlings of ‘Xuegan’ [Citrus sinensis (L.) Osbeck] were irrigated with Mg-deficient (0 mM MgSO₄) or Mg-sufficient (1 mM MgSO₄) nutrient solution for 16 weeks. Thereafter, we first investigated the proteomic responses of C. sinensis roots and leaves to Mg-deficiency using two-dimensional electrophoresis (2-DE) in order to (a) enrich our understanding of the molecular mechanisms of plants to deal with Mg-deficiency and (b) understand the molecular mechanisms by which Mg-deficiency lead to a decrease in photosynthesis.

Results

Fifty-nine upregulated and 31 downregulated protein spots were isolated in Mg-deficient leaves, while only 19 upregulated and 12 downregulated protein spots in Mg-deficient roots. Many Mg-deficiency-responsive proteins were involved in carbohydrate and energy metabolism, followed by protein metabolism, stress responses, nucleic acid metabolism, cell wall and cytoskeleton metabolism, lipid metabolism and cell transport. The larger changes in leaf proteome versus root one in response to Mg-deficiency was further supported by our observation that total soluble protein concentration was decreased by Mg-deficiency in leaves, but unaffected in roots. Mg-deficiency had decreased levels of proteins [i.e. ribulose-1,5-bisphosphate carboxylase (Rubisco), rubisco activase, oxygen evolving enhancer protein 1, photosynthetic electron transfer-like protein, ferredoxin-NADP reductase (FNR), aldolase] involved in photosynthesis, thus decreasing leaf photosynthesis. To cope with Mg-deficiency, C. sinensis leaves and roots might respond adaptively to Mg-deficiency through: improving leaf respiration and lowering root respiration, but increasing (decreasing) the levels of proteins related to ATP synthase in roots (leaves); enhancing the levels of proteins involved in reactive oxygen species (ROS) scavenging and other stress-responsive proteins; accelerating proteolytic cleavage of proteins by proteases, protein transport and amino acid metabolism; and upregulating the levels of proteins involved in cell wall and cytoskeleton metabolism.

Conclusions

Our results demonstrated that proteomics were more affected by long-term Mg-deficiency in leaves than in roots, and that the adaptive responses differed between roots and leaves when exposed to long-term Mg-deficiency. Mg-deficiency decreased the levels of many proteins involved in photosynthesis, thus decreasing leaf photosynthesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1462-z) contains supplementary material, which is available to authorized users.     

Essential mycorrhizal partners of the endemic Chilean orchids Chloraea collicensis and C. gavilu

Orchids are obligate mycoheterotrophic plants, relying on fungal nutrient resources to grow for their entire life or until they develop into photosynthetic seedlings. In Chile, orchids are represented by 7 genera and 63 species, 27 of which are endemic. Some Chilean species are considered endangered or rare, but many are insufficiently known. This study aims to isolate, culture, and identify fungal species found in symbiosis with the endemic Chilean orchids Chloraea collicensis Kraenzl. and Chloraea gavilu Lindl. for their potential to be used in future conservation programs. Roots of both species of orchids were collected in the field and those presenting pelotons were firstly cultured in agar-water and thereafter sub-cultured in potato dextrose agar media. Fungal colony growth was measured under the dissecting microscope. Fungal isolates from C. gavilu showed a higher growth rate than isolates from C. collicensis and could be used as inoculum for seed germination in further studies. Isolated colonies showed morphological characteristics of the form genus Rhizoctonia and presented two nuclei per cell. The ITS-nrDNA sequences confirmed their morphological identification as species of Tulasnella.     

Characterization and Partial Purification of Aldose-6-phosphate Reductase (Alditol-6-Phosphate:NADP 1-Oxidoreductase) from Apple Leaves

The Pereskia are morphologically primitive, leafed members of the Cactaceae. Gas exchange characteristics using a dual isotope porometer to monitor ¹⁴CO₂ and tritiated water uptake, diurnal malic acid fluctuations, phosphoenolpyruvate carboxylase, and malate dehydrogenase activities were examined in two species of the genus Pereskia, Pereskia grandifolia and Pereskia aculeata. Investigations were done on well watered (control) and water-stressed plants. Nonstressed plants showed a CO₂ uptake pattern indicating C₃ carbon metabolism. However, diurnal fluctuations in titratable acidity were observed similar to Crassulacean acid metabolism. Plants exposed to 10 days of water stress exhibited stomatal opening only during an early morning period. Titratable acidity, phosphoenolpyruvate carboxylase activity, and malate dehydrogenase activity fluctuations were magnified in the stressed plants, but showed the same diurnal pattern as controls. Water stress causes these cacti to shift to an internal CO₂ recycling (“idling”) that has all attributes of Crassulacean acid metabolism except nocturnal stomata opening and CO₂ uptake. The consequences of this shift, which has been observed in other succulents, are unknown, and some possibilities are suggested.