Photosynthetic Tissues Research Articles

Locked up Inside the Vessels: Rare Earth Elements Are Transferred and Stored in the Conductive Tissues of the Accumulating Fern Dryopteris erythrosora.

Rare earth elements (REEs) are strategic metals strongly involved in low-carbon energy conversion. However, these emerging contaminants are increasingly disseminated into ecosystems, raising concern regarding their toxicity. REE-accumulating plants are crucial subjects to better understand REE transfer to the trophic chain but are also promising phytoremediation tools. In this analysis, we deciphered REE accumulation sites in the REE-accumulating fern Dryopteris erythrosora by synchrotron X-ray μfluorescence (μXRF). This technique allows a high-resolution and in situ analysis of fresh samples or frozen-hydrated cross sections of different organs of the plant. In the sporophyte, REEs were translocated from the roots to the fronds by the xylem sap and were stored within the xylem conductive system. The comparison of REE distribution and accumulation levels in the healthy and necrotic parts of the frond shed light on the differential mobility between light and heavy REEs. Furthermore, the comparison emphasized that necrotized areas were not the main REE-accumulating sites. Finally, the absence of cell-to-cell mobility of REEs in the gametophyte suggested the absence of REE-compatible transporters in photosynthetic tissues. These results provide valuable knowledge on the physiology of REE-accumulating ferns to understand the REE cycle in biological systems and the expansion of phytotechnologies for REE-enriched or REE-contaminated soils.

Determination of Paraquat in Arabidopsis Tissues and Protoplasts by UHPLC-MS/MS.

Paraquat is a cost-effective herbicide, widely used in many countries, that can induce severe oxidative stress in photosynthetic tissues. Studying plant herbicide resistance or antioxidant stress mechanisms requires determining the cellular paraquat level when plants are treated by paraquat. The traditional isotopic labeling method has the potential risk to cause problems to both human health and the environment. For radioisotope manipulation, special operation spaces and strict environmental inspection are also required. In addition, the radiolabeled paraquat is increasingly hard to buy due to the extended production cycle. Here, we describe a nonradioactive method to determine the paraquat level in a small number of Arabidopsis tissues or protoplasts, using a high resolution ultra-high-performance liquid chromatography (UHPLC)-mass spectrometry (MS)/MS method. This method is highly selective and sensitive, and more environmentally compatible and technically feasible than the isotope detection method.

Predicting ecosystem productivity based on plant community traits.

With the rapid accumulation of plant trait data, major opportunities have arisen for the integration of these data into predicting ecosystem primary productivity across a range of spatial extents. Traditionally, traits have been used to explain physiological productivity at cell, organ, or plant scales, but scaling up to the ecosystem scale has remained challenging. Here, we show the need to combine measures of community-level traits and environmental factors to predict ecosystem productivity at landscape or biogeographic scales. We show how theory can extend the production ecology equation to enormous potential for integrating traits into ecological models that estimate productivity-related ecosystem functions across ecological scales and to anticipate the response of terrestrial ecosystems to global change.

Stomatal pore width and area measurements in Zea mays.

Stomatal pores are adjustable microscopic holes on the surface of photosynthetic tissues that help regulate multiple aspects of plant physiology. Stomatal pores facilitate gas exchange necessary for photosynthesis, water transport, and temperature regulation. Pore size is influenced by many intertwined environmental, molecular, cellular, and physiological cues. Accurate and precise measurements of pore size is important for understanding the mechanisms that adjust pores and plant physiology. Here we investigate whether conventional pore measurements of width are appropriate for the economically important crop plant Zea mays . Our studies demonstrate that pore area is a more sensitive measurement than width in this plant.

Roles of plastid-located phosphate transporters in carotenoid accumulation.

Enhanced carotenoid accumulation in plants is crucial for the nutritional and health demands of the human body since these beneficial substances are acquired through dietary intake. Plastids are the major organelles to accumulate carotenoids in plants and it is reported that manipulation of a single plastid phosphate transporter gene enhances carotenoid accumulation. Amongst all phosphate transport proteins including phosphate transporters (PHTs), plastidial phosphate translocators (pPTs), PHOSPHATE1 (PHO1), vacuolar phosphate efflux transporter (VPE), and Sulfate transporter [SULTR]-like phosphorus distribution transporter (SPDT) in plants, plastidic PHTs (PHT2 & PHT4) are found as the only clade that is plastid located, and manipulation of which affects carotenoid accumulation. Manipulation of a single chromoplast PHT (PHT4;2) enhances carotenoid accumulation, whereas manipulation of a single chloroplast PHT has no impact on carotenoid accumulation. The underlying mechanism is mainly attributed to their different effects on plastid orthophosphate (Pi) concentration. PHT4;2 is the only chromoplast Pi efflux transporter, and manipulating this single chromoplast PHT significantly regulates chromoplast Pi concentration. This variation subsequently modulates the carotenoid accumulation by affecting the supply of glyceraldehyde 3-phosphate, a substrate for carotenoid biosynthesis, by modulating the transcript abundances of carotenoid biosynthesis limited enzyme genes, and by regulating chromoplast biogenesis (facilitating carotenoid storage). However, at least five orthophosphate influx PHTs are identified in the chloroplast, and manipulating one of the five does not substantially modulate the chloroplast Pi concentration in a long term due to their functional redundancy. This stable chloroplast Pi concentration upon one chloroplast PHT absence, therefore, is unable to modulate Pi-involved carotenoid accumulation processes and finally does affect carotenoid accumulation in photosynthetic tissues. Despite these advances, several cases including the precise location of plastid PHTs, the phosphate transport direction mediated by these plastid PHTs, the plastid PHTs participating in carotenoid accumulation signal pathway, the potential roles of these plastid PHTs in leaf carotenoid accumulation, and the roles of these plastid PHTs in other secondary metabolites are waiting for further research. The clarification of the above-mentioned cases is beneficial for breeding high-carotenoid accumulation plants (either in photosynthetic or non-photosynthetic edible parts of plants) through the gene engineering of these transporters.

Adjustments in photosynthetic pigments, PS II photochemistry and photoprotection in a tropical C4 forage plant exposed to warming and elevated [CO2

Global climate change will impact crops and grasslands, affecting growth and yield. However, is not clear how the combination of warming and increased atmospheric carbon dioxide concentrations ([CO2]) will affect the photosystem II (PSII) photochemistry and the photosynthetic tissue photoinhibition and photoprotection on tropical forages. Here, we evaluated the effects of elevated [CO2] (∼600 μmol mol−1) and warming (+2 °C increase temperature) on the photochemistry of photosystem II and the photoprotection strategies of a tropical C4 forage Panicum maximum Jacq. grown in a Trop-T-FACE facility under well-watered conditions without nutrient limitation. Analysis of the maximum photochemical efficiency of PSII (Fv/Fm), the effective PSII quantum yield Y(II), the quantum yield of regulated energy dissipation Y(NPQ), the quantum yield of non-regulated energy dissipation Y(NO), and the malondialdehyde (MDA) contents in leaves revealed that the photosynthetic apparatus of plants did not suffer photoinhibitory damage, and plants did not increase lipid peroxidation in response to warming and [CO2] enrichment. Plants under warming treatment showed a 12% higher chlorophyll contents and a 58% decrease in α-tocopherol contents. In contrast, carotenoid composition (zeaxanthin and β-carotene) and ascorbate levels were not altered by elevated [CO2] and warming. The elevated temperature increased both net photosynthesis rate and aboveground biomass but elevated [CO2] increased only net photosynthesis. Adjustments in chlorophyll, de-epoxidation state of the xanthophylls cycle, and tocopherol contents suggest leaves of P. maximum can acclimate to 2 °C warmer temperature and elevated [CO2] when plants are grown with enough water and nutrients during tropical autumn-winter season.

Mitochondria in photosynthetic cells: Coordinating redox control and energy balance.

In photosynthetic tissues in the light, the function of energy production is associated primarily with chloroplasts, while mitochondrial metabolism adjusts to balance ATP supply, regulate the reduction level of pyridine nucleotides, and optimize major metabolic fluxes. The tricarboxylic acid cycle in the light transforms into a noncyclic open structure (hemicycle) maintained primarily by the influx of malate and the export of citrate to the cytosol. The exchange of malate and citrate forms the basis of feeding redox energy from the chloroplast into the cytosolic pathways. This supports the level of NADPH in different compartments, contributes to the biosynthesis of amino acids, and drives secondary metabolism via a supply of substrates for 2-oxoglutarate-dependent dioxygenase and for cytochrome P450-catalyzed monooxygenase reactions. This results in the maintenance of redox and energy balance in photosynthetic plant cells and in the formation of numerous bioactive compounds specific to any particular plant species. The noncoupled mitochondrial respiration operates in coordination with the malate and citrate valves and supports intensive fluxes of respiration and photorespiration. The metabolic system of plants has features associated with the remarkable metabolic plasticity of mitochondria that permit the use of energy accumulated during photosynthesis in a way that all anabolic and catabolic pathways become optimized and coordinated.

The leaf anatomical trade-offs associated with plant ecological strategy variation

Plant functioning depends on variation in resource economics traits (acquisition vs. conservation) and the size of plants and their parts (the ‘global spectrum of plant form and function’). The anatomical basis of single traits (e.g., leaf mass per area; LMA) is generally understood, but little is known regarding the relationship between anatomical trade-offs and ecological strategies (representing integrated suites of traits). We hypothesised correlations between the relative extent of leaf tissue types and Grime’s Competitor Stress-tolerator Ruderal (CSR) strategies, principally a trade-off between structural (mechanical/fibro-vascular) vs. photosynthetic (chlorenchyma and intercellular airspace; ICAS) tissues, for ecologically contrasting herbaceous angiosperms in northern Italy. Specifically, that in the lamina portion, the trade-off represents the economics spectrum (S-R selection), but in the midvein portion, it reflects the mechanical constraints inherent to supporting large leaves (i.e., varies with C-selection). We used microscopy and image analysis to determine the relative cross-sectional area of tissues from transverse leaf sections (lamina and midvein portions) of angiosperms of contrasting CSR strategies. Principal components analysis (PCA) determined that the main trade-off (PCA1) was between mechanical/fibro-vascular tissues vs. ICAS/epidermis/chlorenchyma, but that this was associated with the economics spectrum (R- to S-selection) in the lamina, and with size (C-selection) for the midvein. A secondary trade-off in both lamina and midvein portions involved ICAS (i.e., the internal gas diffusion pathway) vs. chlorenchyma/epidermis (light capture), associated with S- to R-selection, respectively. Our results confirm the expectation that ecological strategy variation has a basis in underlying trade-offs between tissues with contrasting metabolic/architectural (i.e., economics/size-related) roles.

Early leaf development of Typha domingensis Pers. (Typhaceae)

ABSTRACT Typha domingensis Pers. (cattail) is a globally widespread aquatic plant that causes significant impacts as an invasive species; this ability is dependent on its photosynthetic capacity that is related to leaves. Thus, understanding leaf development is essential for interpreting shoot growth and the formation of its photosynthetic area. This study investigates leaf ontogeny in T. domingensis from early stages until complete development of primary tissues. Plants were collected from natural wetlands and cultivated in a greenhouse. Rhizomes were then selected, and leaves were removed to enable the emergence of new shoots. Rhizome fragments containing leaves were collected at 1-day intervals until day 7 and were subjected to routine procedures in plant microtechnique. New leaves emerged from lateral buds located along the rhizome. The anatomy of scale leaves differs from that of photosynthetic leaves since they contain solid inclusions without palisade parenchyma. Leaf primordia arose laterally from the shoot apical meristem, which was organized as a tunica-corpus. Final leaf shape was influenced by different meristematic zones: the leaf apical meristem, the marginal meristem, the rib meristem, and intercalary meristems. Most leaf tissues developed basipetally, except for xylem and phloem. Within seven days following leaf initiation, all primary tissues were developed and morphologically functional. Leaf formation of Typha domingensis is similar to that of other monocot species. Leaves of T. domingensis develop very early, providing fully functional photosynthetic tissues, which may have implications for its invasive capacity.

Identification and expression analysis of pineapple sugar transporters reveal their role in the development and environmental response.

In plants, sugars are required for several essential functions, including growth, storage, signaling, defense and reproduction. Sugar transporters carry out the controlled movement of sugars from source (leaves) to sink (fruits and roots) tissues and determine the overall development of the plant. Various types of sugar transporter families have been described in plants, including sucrose transporters (SUC/SUT), monosaccharide transporter (MST) and SWEET (from "Sugar Will Eventually be Exported Transporters"). However, the information about pineapple sugar transporters is minimal. This study systematically identified and classified 45 MST and 4 SUC/SUT genes in the pineapple genome. We found that the expression patterns of sugar transporter genes have a spatiotemporal expression in reproductive and vegetative tissues indicating their pivotal role in reproductive growth and development. Besides, different families of sugar transporters have a diel expression pattern in photosynthetic and non-photosynthetic tissues displaying circadian rhythm associated participation of sugar transporters in the CAM pathway. Moreover, regulation of the stress-related sugar transporters during cold stress indicates their contribution to cold tolerance in pineapple. Heterologous expression (yeast complementation assays) of sugar transporters in a mutant yeast strain suggested that SUT1/2 have the ability to transport sucrose, and STP13, STP26, pGlcT-L2 and TMT4 are able to transport glucose, whereas SWEET11/13 transport both sucrose and fructose. The information provided here would help researchers further explore the underlying molecular mechanism involved in the sugar metabolism of pineapple.

Effects of Free Amino Acids, Metallothionein, and Chemical Forms of Heavy Metals on the Accumulation and Detoxification of Cadmium and Chromium in Chinese Goldthread (Coptis chinensis Franch.)

Chinese goldthread (Coptis chinensis Franch.) is an important medicinal plant worldwide. However, its clinical safety is negatively impacted by high cadmium (Cd) and chromium (Cr) levels. Understanding the accumulation pattern and detoxification mechanism of heavy metals, such as Cd and Cr, is important for regulating their transportation and reducing their accumulation in plants. Free amino acids (FAAs), metallothioneins, and chemical forms of heavy metals are closely associated with heavy metal accumulation and detoxification mechanisms. In the present study, we evaluated the uptake of Cd and Cr in Chinese goldthread and characterized the changes in FAA levels, CcMT2, a metallothionein gene, expression under Cd and Cr stress, and Cr chemical forms in various tissues of Chinese goldthread. The majority of Cd and Cr was retained in the roots; this might be the tolerance strategy utilized by Chinese goldthread to protect the aboveground photosynthetic tissues. A chemical continuous extraction method was utilized to analyze the chemical forms of Cr, and the results suggested that Cr was primarily fixed by oxalate in all tissues, and after Cr treatment, Cr tended to combine with phosphate to form an insoluble complex that reduced the toxicity and bioavailability of Cr in Chinese goldthread. The accumulation of Cd and Cr was significantly positively correlated with valine, histidine, threonine, tyrosine, and serine levels and significantly negatively correlated with glutamic acid and alanine levels. The variation in proline levels under Cd stress was different than that under Cr stress. FAAs might affect the accumulation of and resistance to Cd and Cr through various detoxification strategies, such as chelation with heavy metals ions and conversion into the required products. Furthermore, CcMT2 was isolated for the first time and found to be dominantly expressed in leaves. CcMT2 was induced under Cd and Cr stress in all plant tissues, indicating its role in the accumulation of and tolerance to Cd and Cr.

Biogeographical patterns of community-level content of N and P and their stoichiometric ratios in subtropical forest floor bryophytes

• Biogeographical patterns of nutrients for bryophytes remain largely unknown. • Relationships between bryophyte nutrients and environmental factors were calculated. • Bryophyte N and P content increased with increasing elevations and decreasing MAT. • Nutrient content of bryophytes and those of soil were positively associated. • Soil nutrient content and MAT were more important determinants of bryophyte N and P. With special phylogenetic status, life history, morphology, adaptations, and ecophysiological strategies, bryophytes differ from vascular plants in terms of the requirement, uptake, allocation, and releasing rate of nutrients. However, biogeographical patterns of nutrients for bryophytes remain largely unknown. The present study determined and calculated the community-level carbon (C), nitrogen (N), and phosphorus (P) content and their stoichiometric ratios of the photosynthetic tissues of the subtropical forest-floor bryophytes collected from 295 sites in Sichuan province, China. We aimed to find out: 1) the geographical patterns in the content of N and P and the stoichiometric ratio of N to P for bryophytes; 2) the effects of environmental factors (climate, soil nutrient content, and stand attributes); and 3) the driving factors. We found that the bryophytes collected from the western plateau had a higher P content and a lower N:P than those from the eastern basin. The bryophytes’ N and P content generally increased with increasing elevations and decreasing mean annual temperature (MAT) and potential evaporation, while the N:P ratio decreased with decreasing elevations. But these patterns were scale-dependent. Nutrient content of bryophytes and those of soil were positively associated. Bryophyte N content was unrelated to mean annual precipitation (MAP) and stand attributes, while P content was negatively related to MAP and shrub and herb cover. Among the environmental factors at play, soil nutrient content and MAT were more important determinants of bryophyte N and P content than MAP and stand attributes. This study contributes to a better understanding of the relationships among environmental factors and bryophyte N and P at a basin-mountain transition zone and provides evidence to quantitatively assess the ecological role of bryophytes in nutrient cycling in the ecosystem.

Effect of Salinity on Leaf Functional Traits and Chloroplast Lipids Composition in Two C3 and C4 Chenopodiaceae Halophytes.

Salt stress is one of the most common abiotic kinds of stress. Understanding the key mechanisms of salt tolerance in plants involves the study of halophytes. The effect of salinity was studied in two halophytic annuals of Chenopodiaceae Salicornia perennans Willd. and Climacoptera crassa (Bied.) Botsch. These species are plants with C3 and C4-metabolism, respectively. We performed a comprehensive analysis of the photosynthetic apparatus of these halophyte species at different levels of integration. The C3 species S. perennans showed larger variation in leaf functional traits—both at the level of cell morphology and membrane system (chloroplast envelope and thylakoid). S. perennans also had larger photosynthetic cells, by 10–15 times, and more effective mechanisms of osmoregulation and protecting cells against the toxic effect of Na+. Salinity caused changes in photosynthetic tissues of C. crassa such as an increase of the mesophyll cell surface, the expansion of the interface area between mesophyll and bundle sheath cells, and an increase of the volume of the latter. These functional changes compensated for scarce CO2 supply when salinity increased. Overall, we concluded that these C3 and C4 Chenopodiaceae species demonstrated different responses to salinity, both at the cellular and subcellular levels.

Similar structural complexity of phenols in plant morphotypes with contrasting soluble phenol concentration and richness in arid rangelands of Patagonia

Phenols can play a significant role in plant tolerance of drought and herbivory. We assessed the concentration, richness and structural complexity of soluble phenols (hereafter phenols) in leaves of different species representing different plant morphotypes of arid ecosystems. We selected seven species representative of the three main plant morphotypes of the Patagonia Monte (Argentina): tall evergreen shrubs (TES), medium evergreen shrubs (MES), and perennial grasses (PG). These morphotypes differed in plant height, rooting depth, proportion of photosynthetic tissues, specific leaf area, and concentration of phenols and N in leaves. We found 48 compounds belonging to six types of phenols differing in structural complexity (low complexity: simple phenols, phenolic acids and phenolic esters; medium complexity: hydroxycinnamic acids and phenylpropenes; and high complexity: quinones, flavonols and flavones). Phenols of low and medium complexity were the most abundant in all morphotypes, while those of high complexity, probably the most costly for plants, were nearly exclusive of some tall evergreen shrubs. In general, PG, MES and TES had low, intermediate and high phenol concentration (8.5, 27.2, 202.5 mg g−1DW, respectively) and richness (15, 25, 37 compounds, respectively) in leaves. The richness of phenols was significantly and positively related to phenol concentration. However, we did not find distinctive phenol compound patterns among morphotypes. Our results suggest that drought and, to some extent, herbivory have exerted selective selection pressure on richness and phenol concentration in leaves of contrasting morphotypes but the type of phenols accumulated probably depends on intrinsic species attributes within each morphotype.

A win-win scenario for photosynthesis and the plasma membrane H+ pump.

In plants, cytosolic and extracellular pH homeostasis are crucial for various physiological processes, including the uptake of macronutrients and micronutrients, cell elongation, cell expansion, and enzyme activity. Proton (H+) gradients and the membrane potential are generated by a H+ pump consisting of an active primary transporter. Plasma membrane (PM) H+-ATPase, a PM-localized H+ pump, plays a pivotal role in maintaining pH homeostasis in plant cells and extracellular regions. PM H+-ATPase activity is regulated by protein abundance and by post-translational modifications. Several stimuli have been found to activate the PM H+-ATPase through phosphorylation of the penultimate threonine (Thr) of the carboxy terminus. Light- and photosynthesis-induced phosphorylation of PM H+-ATPase are conserved phenomena among various plant species. In this work, we review recent findings related to PM H+-ATPase regulation in the photosynthetic tissues of plants, focusing on its mechanisms and physiological roles. The physiological roles of photosynthesis-dependent PM H+-ATPase activation are discussed in the context of nitrate uptake and cytoplasmic streaming in leaves.

Responses of chlorophyll fluorescence and non-structural carbohydrate accumulation of Castanopsis kawakamii seedlings to seed dispersal positions

When seeds fallen from the mother trees, their initial contact physical environment was litter or soil. The dispersal positions of seeds (seeds positioned on top of the litter, the soil surface and beneath the litter) determine the process of their natural regeneration. We simulated three different dispersal positions of Castanopsis kawakamii, including seeds positioned on top of the litter (2 and 4 cm litter was placed below the seed layer), soil surface (without litter), and seeds beneath the litter (2, 4, 6 and 8 cm litter covers in the upper layer of seeds). We examined the effects of seed dispersal position on the chlorophyll fluorescence characteristics, non-structural carbohydrate, specific leaf area, leaf dry matter content and nutrient content of seedlings. The results showed that leaf nitrogen content per area of seedlings had significantly positive correlation with soluble sugar content, non-structural carbohydrate content, and negative correlation with specific leaf area across different dispersal positions. Seedlings of the moderate litter cover (2 and 4 cm) adopted resource acquisitive strategies by increasing relative chlorophyll content, soluble sugar content, non-structural carbohydrate content, leaf dry matter content, leaf nitrogen content and phosphorus contents per area, and decreasing specific leaf area to achieve their demands for rapid growth. Seedlings grew on soil surface and beneath the deep litter (6 and 8 cm) adopted the resource conservative strategies with higher leaf nitrogen content per mass and specific leaf area, lower leaf dry matter content, and non-structural carbohydrate content to intercept more effective light resources to compensate for the shady environment brought by deep litter. This would further decrease the probability of seedling mortality due to 'carbon starvation'. Seedlings under litter layer stored starch in leaf, and reduced the energy consumption of photosynthetic tissues (low PSⅡ maximum photochemical efficiency) to maintain seedling growth. Comprehensive analysis of entropy method indicated that low amount of litter cover (2 cm) significantly promoted seedling growth of C. kawakamii. In the future, we could regulate the thickness of litter layer to promote the growth and regeneration of C. kawakamii seedlings in natural forest.

Multi-level physiological and morphological adjustment of Haloxylon ammodendron related to groundwater drawdown in a desert ecosystem

Climate change and anthropogenic exploitation will increase groundwater lowering rates and aggravate groundwater shortage, particularly in desert ecosystems that rely heavily on groundwater. We conducted detailed studies about morphological and ecophysiological traits of two Haloxylon ammodendron communities across different groundwater depths in the Gurbantonggut Desert in China during an extreme drought period. When photosynthetic twig temperatures exceeded 45°C, photosynthesis was suppressed and dropped to zero, while stomatal conductance and transpiration rate increased rapidly. This decoupled behavior may cool photosynthetic tissues to prevent permanent damage. The optimum temperature decreased by ∼3°C in H. ammodendron at deep groundwater sites with less soil-water availability, which contributed to improving water use efficiency (WUE) at lower temperatures. H. ammodendron at the deep groundwater site had lower photosynthetic twig size and plant height while higher proportion of twig and branch biomass, which induced a denser canopy structure, and they had greater leaf dry mass content, photosynthetic pigments, and non-structural carbohydrates, and more negative predawn shoot water potential. Overall, our study indicates that H. ammodendron could alleviate adverse effects of reduced soil water availability and maintain photosynthetic capacity through multiple morphological and physiological adjustments. This establishes the basis for predicting responses of desert shrubs to groundwater drawdown.

Species composition and identification of pathogens of real powdery mildew of pumpkin crops

When cultivating pumpkin crops in most agricultural regions of the world, one of the most aggressive diseases is real powdery mildew, the damage of plants in which, under optimal soil and climatic conditions for the pathogen, reaches 100%. In the open and protected ground, among the cultivated representatives of the Cucurbitaceae family, the most widespread and harmful are the species Sphaerotheca fuliginea (Schlecht ex Fr.) Poll and Erysiphe cichoracearum f. sp. cucurbitacearum (DC ex Merat). In regions where both phytopathogens are present, mixed infections may occur, making identification difficult, and, accordingly, further plant protection measures. The pathogens of this powdery mildew of pumpkin crops have different requirements for temperature and humidity. During the growing season, there may be a change in species composition when conditions change, for example, when a new season begins. Symptoms of the disease in the form of a white or yellowish powdery plaque in the form of rounded spots (mainly on the leaves) can manifest themselves at all stages of plant development, the susceptibility of which increases by the beginning of fruiting. According to biological characteristics, S. fuliginea and E. cichoracearum are obligate biotrophic pathogens, unable to exist independently without living photosynthetic tissue, except for the wintering (sexual) stage of teleomorphs in the form of globular kleistothecia. At this stage, it is not difficult to differentiate pathogens by the morphology of kleistothecium. When analyzing the plant material of melons with the naked eye, S. fuliginea and E. cichoracearum cause similar symptoms of damage, but by microscopy these organisms can be distinguished by a complex of morphological characteristics. Taxonomically significant features are: the location of the mycelium, the formation of conidia (single or chain), the presence or absence of noticeable fibrosin bodies, the features of the appressoria, the size and shape of the conidia, as well as the position and type of their sprout tubes. The works of Russian and foreign scientists have shown the possibility of determining the types and physiological races of pathogens using an indirect method: reactions to differentiator plants. To date, about 30 physiological races of the pathogen Podosphaera xanthii (Sphaerotheca fuliginea) and 2 races of E. cichoracearum are known. However, this method does not always correlate with the methods of molecular analysis. Determination of the species composition of powdery mildew pathogens is a starting point for the development of a further strategy for the cultivation of pumpkin crops and in breeding work for resistance to this disease.

Light regulates xylem cell differentiation via PIF in Arabidopsis.

The balance between cell proliferation and differentiation in the cambium defines the formation of plant vascular tissues. As cambium cells proliferate, subsets of daughter cells differentiate into xylem or phloem. TDIF-PXY/TDR signaling is central to this process. TDIF, encoded by CLE41 and CLE44, activates PXY/TDR receptors to maintain proliferative cambium. Light and water are necessary for photosynthesis; thus, vascular differentiation must occur upon light perception to facilitate the transport of water and minerals to the photosynthetic tissues. However, the molecular mechanism controlling vascular differentiation in response to light remains elusive. In this study we show that the accumulation of PIF transcription factors in the dark promotes TDIF signaling and inhibits vascular cell differentiation. On the contrary, PIF inactivation by light leads to a decay in TDIF activity, which induces vascular cell differentiation. Our study connects light to vascular differentiation and highlights the importance of this crosstalk to fine-tune water transport.

Post‐fire recovery of soil microbial functions is promoted by plant growth

AbstractForest fires can alter the biological properties of soils. There is increasing evidence that fires cause a shift in soil microbial communities, which play a central role in forest carbon and nutrient cycling. In this study, we evaluate the effect of soil heating on soil microbial functions. We hypothesised that fire reduces the catabolic functional diversity of soil, and that post‐fire plant growth enhances its recovery. To test this, we experimentally heated a forest soil at 200°C (T200) or 450°C (T450). Heated and unheated soils were then incubated in tubs with or without live grass (Lolium perenne L.). We determined the functional profiles by measuring the substrate‐induced respiration (SIR) using the Microresp™ technique and analysed nutrient availability at the end of the incubation. At both temperatures, soil heating altered the respiration responses to substrate additions and the catabolic functional diversity of soils. Functional diversity was initially reduced in T200 soils but recovered at the end of the incubation. In contrast, T450 soils initially maintained the catabolic functional diversity, but decreased at the end of the incubation. Heating‐induced nutrient availability stimulated the growth of grass, which in turn increased the response to several substrates and increased the functional diversity to values similar to the unheated controls. Our results suggest that fire‐driven alteration of soil microbial communities has consequences at a functional level, and that the recovery of plant communities enhances the recovery of soil microbial functions.Highlights Soil experimental heating altered microbial functions and reduced soil functional diversity. Soil heating also increased nutrient availability, enhancing plant growth. Growth of plants promoted the recovery of soil functional diversity. Post‐fire recovery of functional diversity may be related to the recovery of photosynthetic tissues.