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Hydathodes are usually associated with water exudation in plants. However, foliar water uptake (FWU) through the hydathodes has long been suspected in the leaf‐succulent genus Crassula (Crassulaceae), a highly diverse group in southern Africa, and, to our knowledge, no empirical observations exist in the literature that unequivocally link FWU to hydathodes in this genus. FWU is expected to be particularly beneficial on the arid western side of southern Africa, where up to 50% of Crassula species occur and where periodically high air humidity leads to fog and/or dew formation. To investigate if hydathode‐mediated FWU is operational in different Crassula species, we used the apoplastic fluorescent tracer Lucifer Yellow in combination with different imaging techniques. Our images of dye‐treated leaves confirm that hydathode‐mediated FWU does indeed occur in Crassula and that it might be widespread across the genus. Hydathodes in Crassula serve as moisture‐harvesting structures, besides their more common purpose of guttation, an adaptation that has likely played an important role in the evolutionary history of the genus. Our observations suggest that ability for FWU is independent of geographical distribution and not restricted to arid environments under fog influence, as FWU is also operational in Crassula species from the rather humid eastern side of southern Africa. Our observations point towards no apparent link between FWU ability and overall leaf surface wettability in Crassula. Instead, the hierarchically sculptured leaf surfaces of several Crassula species may facilitate FWU due to hydrophilic leaf surface microdomains, even in seemingly hydrophobic species. Overall, these results confirm the ecophysiological relevance of hydathode‐mediated FWU in Crassula and reassert the importance of atmospheric humidity for some arid‐adapted plant groups. Summary Statement: This study demonstrates that foliar water uptake (FWU) through hydathodes, previously suspected but unconfirmed, is indeed operational in most Crassula species. This phenomenon occurs across different habitats and highlights the ecophysiological relevance of atmospheric humidity for these plants. [ABSTRACT FROM AUTHOR]

Plant diseases are an important threat to food production. While major pathogenicity determinants required for disease have been extensively studied, less is known on how pathogens thrive during host colonization, especially at early infection stages. Here, we used randomly barcoded-transposon insertion site sequencing (RB-TnSeq) to perform a genome-wide screen and identify key bacterial fitness determinants of the vascular pathogen Xanthomonas campestris pv campestris (Xcc) during infection of the cauliflower host plant (Brassica oleracea). This high-throughput analysis was conducted in hydathodes, the natural entry site of Xcc, in xylem sap and in synthetic media. Xcc did not face a strong bottleneck during hydathode infection. In total, 181 genes important for fitness were identified in plant-associated environments with functional enrichment in genes involved in metabolism but only few genes previously known to be involved in virulence. The biological relevance of 12 genes was independently confirmed by phenotyping single mutants. Notably, we show that XC_3388, a protein with no known function (DUF1631), plays a key role in the adaptation and virulence of Xcc possibly through c-di-GMP-mediated regulation. This study revealed yet unsuspected social behaviors adopted by Xcc individuals when confined inside hydathodes at early infection stages.

Pseudomonas simiae WCS417 is a plant growth–promoting rhizobacterium that improves plant health and development. In this study, we investigate the early leaf responses of Arabidopsis thaliana to WCS417 exposure and the possible involvement of formate dehydrogenase (FDH) in such responses. In vitro–grown A. thaliana seedlings expressing an FDH::GUS reporter show a significant increase in FDH promoter activity in their roots and shoots after 7 days of indirect exposure (without contact) to WCS417. After root exposure to WCS417, the leaves of FDH::GUS plants grown in the soil also show an increased FDH promoter activity in hydathodes. To elucidate early foliar responses to WCS417 as well as FDH involvement, the roots of A. thaliana wild-type Col and atfdh1-5 knock-out mutant plants grown in soil were exposed to WCS417, and proteins from rosette leaves were subjected to proteomic analysis. The results reveal that chloroplasts, in particular several components of the photosystems PSI and PSII, as well as members of the glutathione S-transferase family, are among the early targets of the metabolic changes induced by WCS417. Taken together, the alterations in the foliar proteome, as observed in the atfdh1-5 mutant, especially after exposure to WCS417 and involving stress-responsive genes, suggest that FDH is a node in the early events triggered by the interactions between A. thaliana and the rhizobacterium WCS417. [Graphic: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Toothed leaf margins are common (∼36%) in the New Zealand indigenous flora, and are most abundant in cool forests with high rainfall. Toothed margins are often associated with hydathodes, specialised structures that release water and solutes to maintain positive xylem pressure. However, the presence of hydathodes is mainly known from herbaceous plants. Here we investigate the presence and morphology of hydathodes in indigenous woody species representing 25 families, 33 genera and 57 species, with toothed and entire leaf margins. We tested whether toothed leaf margins on predominantly evergreen species are associated with hydathodes. Two types of structures on leaves were recognised: laminar hydathodes, water pores larger than normal stomata and associated with veins, and hydathodes positioned at the terminus of leaf teeth serviced by principal veins. Laminar hydathodes occur more frequently, but not exclusively, on toothed leaves (on 61.8% of toothed species vs. 48.0% of entire-margined species). Leaf tooth hydathodes are complex structures with undifferentiated, porous tissue plugs linked to splayed vein termini of vessel elements and often form a distinctive cap on leaf teeth. Tooth hydathodes occur on ∼90% of the serrated leaves species sampled. Ontogenetic differences in hydathode occurrence were noted in Alectryon excelsus as leaf morphology changes with plant age from a serrated to a non-serrated form. Quintinia acutifolius showed a similar pattern between individuals with different leaf morphologies. In our sampled dataset, tree species with any type of hydathode occur in areas with a higher ratio of rainfall to potential evapotranspiration than tree species without hydathodes. This pattern was not observed in shrubs. The strong association between marginal hydathodes and toothed leaves in New Zealand trees, plus the association with higher rainfall environments, suggests that these structures function to release hydraulic water pressure in plants on periodically saturated soils in high rainfall zones. [ABSTRACT FROM AUTHOR]

This study presents the first comparative analysis of the leaf secretory structures across Asteraceae. In this work, the leaf secretory structures of more than 500 species of 35 of the 40 tribes and 11 of the 13 subfamilies of Asteraceae are described and compared to evaluate their diversity at the tribe level and to identify evolutionary patterns. Leaf secretory structures are present in 28 of the 35 analyzed tribes and correspond to canals (recorded in 17 tribes), secretory cavities (1 tribe), hydathodes (19 tribes), laticifers (4 tribes) and glandular trichomes (24 tribes). Canals are mostly associated with vascular bundles and predominate in Asteroideae, while cavities were only present within Tageteae. Hydathodes occur in leaves without divisions and with well-developed teeth. Laticifers were observed only in the tribes of Cichorioideae. Seven glandular trichome morphotypes were differentiated by their cellular composition and shape. These observations together with the available information showed that secretory structures are found in 80% of the Asteraceae tribes. Four of the 40 tribes did not present any type of secretory structure. Our study reveals that almost all of the tribes possess one to three types of secretory structures, and are absent in some early-diverging clades. Character evolution analyses show that glandular trichomes are plesiomorphic in Asteraceae. This study found that secretory structures prevail in late-diverging lineages and were taxonomically informative at different levels. Our comparative study of the secretory structures in Asteraceae is essential for the standardization of its terminology and will provide a frame of reference for future studies. [ABSTRACT FROM AUTHOR]

The digestive organs of carnivorous plants have external (abaxial) glands and trichomes, which perform various functions. Dionaea muscipula Ellis (the Venus flytrap) is a model carnivorous plant species whose traps are covered by external trichomes. The aim of the study was to fill in the gap regarding the structure of the stellate outer trichomes and their immunocytochemistry and to determine whether these data support the suggestions of other authors about the roles of these trichomes. Light and electron microscopy was used to show the trichomes' structure. Fluorescence microscopy was used to locate the carbohydrate epitopes that are associated with the major cell wall polysaccharides and glycoproteins. The endodermal cells and internal head cells of the trichomes were differentiated as transfer cells, and this supports the idea that stellate trichomes transport solutes and are not only tomentose-like trichomes. Trichome cells differ in the composition of their cell walls, e.g., the cell walls of the internal head cells are enriched with arabinogalactan proteins (AGPs). The cell walls of the outer head cells are poor in both low and highly homogalacturonans (HGs), but the immature trichomes are rich in the pectic polysaccharide (1–4)–β-D-galactan. In the immature traps, young stellate trichomes produce mucilage which may protect the trap surface, and in particular, the trap entrance. However, the role of these trichomes is different when the outer head cells collapse. In the internal head cells, a thick secondary wall cell was deposited, which together with the thick cell walls of the outer head cells played the role of a large apoplastic space. This may suggest that mature stellate trichomes might function as hydathodes, but this should be experimentally proven. [ABSTRACT FROM AUTHOR]

Guttation is the mechanism by which liquid exudes from hydathodes located on the tip, along the margins, and on the adaxial and abaxial surfaces of leaves. In contrast to stomata, hydathodes, also known as water stomata or water pores, are often open, representing the path of least resistance to liquid outflow from them. Guttation fluids are made up of several organic compounds. This paper focuses on the defensive properties of the chemical compositions of the guttation extracts of Oryza sativa, Momordica charantia, Luffa acutnugula, and Ricinus communis extracted using five different solvents, which were analyzed using Gas Chromatography–Mass Spectrometry (GC-MS). The mass spectra of the compounds present in the guttation fluids were matched by the National Institute of Standards and Technology (NIST) library. GC-MS analysis of guttation fluid extracts of crop plants revealed the existence of compounds with antifungal and antimicrobial properties which may act as barriers to pathogens. The numerous compounds found in plant extracts, such as fatty acids, organic acids, and terpenoids, have a wide range of protective activities and mechanisms that can serve as the first line of defense against pests and diseases. [ABSTRACT FROM AUTHOR]

Background and Aims Ferns are the second largest group of vascular plants and are distributed nearly worldwide. Although ferns have been integrated into some comparative ecological studies focusing on hydathodes, there is a considerable gap in our understanding of the functional anatomy of these secretory tissues that are found on the vein endings of many fern leaves. In this study, we aimed to investigate the phylogenetic distribution, structure and function of fern hydathodes. Methods We performed a global review on fern hydathodes and their phylogenetic distribution, carried out an ancestral character state reconstruction, and studied the structure, guttation and elemental composition of salt residues of eight species, and the diurnal patterns of xylem pressure of two species. Key Results Hydathodes are known from 1189 fern species, 92 genera and 19 families of 2 orders, Equisetales and Polypodiales. Stochastic character mapping indicated multiple gains and losses of hydathodes at the genus level, occurring especially during the last 50 million years of fern evolution. Hydathodes were located on the adaxial leaf surface and characterized by a cytoplasm-rich, pore-free epidermis, and became functional for several weeks after nearly complete leaf expansion. In two species, positive xylem pressure built up at night, potentially facilitating guttation. Guttation fluid was rich in Ca and often Si, but also contained P, Mg, Na and Al. Conclusions Stochastic character mapping and the structural and functional diversity of hydathodes indicate multiple origins, and their presence/absence in closely related taxa implies secondary losses during fern evolution. Positive xylem pressure and high air humidity play an important role as drivers of guttation. Hydathodes may contribute to the regulation of leaf nutrient stoichiometry by the release of excessive compounds and minerals other than waste products, but the presence of essential chemical elements in salt residues also indicates possible leakage. [ABSTRACT FROM AUTHOR]

Saxifraga paniculata is a subalpine succulent perennial plant arranged in a rosette that is usually found in shallow soil among limestone rocks. Stereoscopic, light and scanning electron microscopy were used to describe the anatomical structure of S. paniculata leaves, paying special attention to structures related to CaCO3 (calcium carbonate) release. Anomocytic stomata are unevenly distributed on each leaf face, being absent in the lower third. The basal leaf margin presents translucent pluricellular trichomes of variable length and width. Towards the apical margin, trichomes become teeth. Both trichomes and teeth are completely covered with whitish CaCO3 crystals. Each tooth has a circular cavity connected to a single hydathode through pores. Clearing treatment revealed camptodromous leaf venation. Anatomical structure shows a bifacial cross-section with spongy mesophyll cells at basal part, becoming heterogeneous at the apex with palisade mesophyll on the adaxial face. Hydathodes are epithematic and connected to outer cavities via two kidney-shaped guard cells showing large substomatal cavity. The epithem is surrounded by a thickened sheath and is formed of highly packed elongated cells with interspersed tracheary elements. CaCO3 deposits consist of microscopic crystals with varying geometries, of which the rhombus is the basic unit. [ABSTRACT FROM AUTHOR]

Saxifraga paniculata is a subalpine succulent perennial plant arranged in a rosette that is usually found in shallow soil among limestone rocks. Stereoscopic, light and scanning electron microscopy were used to describe the anatomical structure of S. paniculata leaves, paying special attention to structures related to CaCO3 (calcium carbonate) release. Anomocytic stomata are unevenly distributed on each leaf face, being absent in the lower third. The basal leaf margin presents translucent pluricellular trichomes of variable length and width. Towards the apical margin, trichomes become teeth. Both trichomes and teeth are completely covered with whitish CaCO3 crystals. Each tooth has a circular cavity connected to a single hydathode through pores. Clearing treatment revealed camptodromous leaf venation. Anatomical structure shows a bifacial cross-section with spongy mesophyll cells at basal part, becoming heterogeneous at the apex with palisade mesophyll on the adaxial face. Hydathodes are epithematic and connected to outer cavities via two kidney-shaped guard cells showing large substomatal cavity. The epithem is surrounded by a thickened sheath and is formed of highly packed elongated cells with interspersed tracheary elements. CaCO3 deposits consist of microscopic crystals with varying geometries, of which the rhombus is the basic unit. [ABSTRACT FROM AUTHOR]

Premise: Extrafloral nectaries have mainly been studied in angiosperms, but have also been reported in 39 fern species. Here we provide a global review of nectaries in ferns and examined their structure, function, and nectar sugar composition in two genera. Methods: We searched in the literature and living plant collections of botanical gardens for indications of fern nectaries, observed nectar‐feeding animals, studied the morphoanatomy in the two genera Aglaomorpha and Campyloneurum, and analyzed the total sugar concentrations and ratios of 16 species. Diurnal nectar release was observed with time‐lapse photography. Results: We found evidence for nectaries in 101 species of ferns from 11 genera and 6 families. Most of the nectary‐bearing species were tree ferns (Cyatheaceae) and epiphytic ferns of the family Polypodiaceae. Nectaries consisted of cytoplasm‐rich parenchyma with large nuclei and an epidermis with or without stomata, were attached to amphiphloic vascular bundles, and released nectar on the lower leaf surface mainly on expanding leaves during the night. Sugar concentrations varied between species (3.8–15.3%) but not between genera, and were sucrose‐dominant (3 spp.), sucrose‐rich (7), or hexose‐rich (3). In the greenhouse, introduced ants, scale insects, and snails fed on the nectar. Conclusions: The wide taxonomic distribution, variable morphology, locations, and sugar compositions point to multiple evolutionary origins of fern nectaries. Nectar release in young leaves might attract mutualistic ants to protect leaves against herbivores only during this most vulnerable developmental stage. Even ex‐situ, fern nectar is a valuable food source because it attracted several opportunistic animal species. [ABSTRACT FROM AUTHOR]

The digestive organs of carnivorous plants have external (abaxial) glands and trichomes, which perform various functions. Dionaea muscipula Ellis (the Venus flytrap) is a model carnivorous plant species whose traps are covered by external trichomes. The aim of the study was to fill in the gap regarding the structure of the stellate outer trichomes and their immunocytochemistry and to determine whether these data support the suggestions of other authors about the roles of these trichomes. Light and electron microscopy was used to show the trichomes’ structure. Fluorescence microscopy was used to locate the carbohydrate epitopes that are associated with the major cell wall polysaccharides and glycoproteins. The endodermal cells and internal head cells of the trichomes were differentiated as transfer cells, and this supports the idea that stellate trichomes transport solutes and are not only tomentose-like trichomes. Trichome cells differ in the composition of their cell walls, e.g., the cell walls of the internal head cells are enriched with arabinogalactan proteins (AGPs). The cell walls of the outer head cells are poor in both low and highly homogalacturonans (HGs), but the immature trichomes are rich in the pectic polysaccharide (1–4)–β-D-galactan. In the immature traps, young stellate trichomes produce mucilage which may protect the trap surface, and in particular, the trap entrance. However, the role of these trichomes is different when the outer head cells collapse. In the internal head cells, a thick secondary wall cell was deposited, which together with the thick cell walls of the outer head cells played the role of a large apoplastic space. This may suggest that mature stellate trichomes might function as hydathodes, but this should be experimentally proven.

Hydathodes are typically found at leaf teeth in vascular plants and are involved in water release to the outside. Although morphological and physiological analysis of hydathodes has been performed in various plants, little is known about the genes involved in hydathode function. In this study, we performed fluorescent protein-based imaging and tissue-specific RNA-seq analysis in Arabidopsis hydathodes. We used the enhancer trap line E325, which has been reported to express green fluorescent protein (GFP) at its hydathodes. We found that E325-GFP was expressed in small cells found inside the hydathodes (named E cells) that were distributed between the water pores and xylem ends. No fluorescence of the phloem markers pSUC2:GFP and pSEOR1:SEOR1-YFP was observed in the hydathodes. These observations indicate that Arabidopsis hydathodes are composed of three major components: water pores, xylem ends, and E cells. In addition, we performed transcriptome analysis of the hydathode using the E325-GFP line. Microsamples were collected from GFP-positive or -negative regions of E325 leaf margins with a needle-based device (~130 µm in diameter). RNA-seq was performed with each single microsample using a high-throughput library preparation method called Lasy-Seq. We identified 72 differentially expressed genes. Among them, 68 genes showed significantly higher and four genes showed significantly lower expression in the hydathode. Our results provide new insights into the molecular basis for hydathode physiology and development. [ABSTRACT FROM AUTHOR]

Leaf teeth, i.e. projections of the leaf margin, are common among angiosperms. These structures may differ in several aspects, e.g. in the presence or absence of an associated gland. Cucurbitoid teeth, which have an associated gland, have been reported to species of Datiscaceae, Begoniaceae and Cucurbitaceae, all from order Cucurbitales. However, no structural characterization has ever been made to confirm the nature of such associated gland in species of Cucurbitaceae; rather, studies so far have merely reported the occurrence of guttation. We aimed to anatomically characterize and identify the nature of glands associated with cucurbitoid teeth in Cucurbitaceae species. Margin samples of leaves at different developmental stages were obtained from seven Cucurbitaceae species, fixed in FAA and processed following usual procedures in optical and scanning electron microscopies. Saplings of Cucumis sativus were placed in a humidity chamber to induce guttation for ulterior chemical characterization of the exudate. Hydathodes were confirmed to occur in all studied species. Their structure consists of an uniseriate epidermis with water pores, reduced epithem, absent sheath and terminal vascularization being formed exclusively by xylem. The presence of sugars in the exudate, which could lead to mistaking hydathodes for nectaries, was ruled out by glucose strip tests. We have characterized, for the first time, the structure of hydathodes in the Cucurbitaceae, thereby elucidating the structure of the glands associated with cucurbitoid teeth. Investigating tooth structure in the Begoniaceae and Datiscaceae should contribute to better knowing the order through taxonomic and biological perspectives. [ABSTRACT FROM AUTHOR]

Leaf teeth are projections on the leaf blade margin. They are structurally variable, with characters that are important for taxonomy and phylogeny, but there is a paucity of information on the anatomy of these structures and little understanding of the features and their functions. Here we describe and compare the leaf tooth anatomy of 47 eudicot species. Toothed margin samples from leaves at different developmental stages were collected, fixed and studied under light and scanning electron microscopy. We identified eight leaf tooth morphotypes, six of which occurred with glands. Hydathodes were the most common glands, being found in 11 species; colleters were found in ten species and extrafloral nectaries were found in two species. Cunonioid teeth either devoid of glands or associated with hydathodes were found in Lamiales, Asterales and Apiales. Dillenioid teeth associated with hydathodes were found in Dilleniales. Spinose teeth associated with colleters were found in Aquifoliales. In rosids, we found begonioid, malvoid, theoid, urticoid and violoid teeth, which may be associated with either colleters or nectaries or lack an associated gland. For each family studied, there was only one type of association between gland and tooth, demonstrating the systematic potential of these glands in eudicots. [ABSTRACT FROM AUTHOR]

• Melpomene peruviana is one of the toughest ferns adapted to xeric environments. • Morpho-anatomical xeromorphic features allow this species to reduce water loss. • It accumulates compounds well known by their antioxidant and water-holding capacity. Melpomene peruviana is one of the ecologically toughest fern species that prospers under climatically extreme conditions between 3400-5200 meters above sea level and occasionally in dry areas at lower elevations. To gain a better understanding of the adaptations that allow this species to withstand such extreme environmental conditions, we investigated the anatomy and histochemistry of the sporophyte of three populations of M. peruviana. All plant organs exhibited thick cuticles, and vascular bundles surrounded by a ring or cap of sclereids and suberized endodermis. Roots also showed an exodermis with U-shaped thickening. The sclereids and the chlorenchyma of the leaf mesophyll were rich in phenolic compounds. Tannins were detected in the spongy parenchyma close to the vascular bundles of the leaf. Hydathodes revealed a cutinized endodermal layer and the presence of flavonoids, lipidic/terpenoid droplets, and free sugars in the epidermis and parenchyma cells. Rhizome scales had basal idioblasts and apical clavate glands with complex contents rich in phenolic compounds, lipids, terpenes, mucilaginous polysaccharides and proteins. Some of the observed morpho-anatomical characteristics such as microphylly, small stomata in high densities, thick cuticles and sclerenchyma close to the vascular tissue, reduce water loss by evapotranspiration and correspond to typical xeromorphic fern features. Among the histochemical characteristics, mucilaginous polysaccharides may act as gels to absorb and retain water while phenolic compounds are recognized for their antioxidant activity. The three populations exhibited a remarkable uniformity concerning their histochemical assays, stomatal dimensions and densities, and tissue thickness. The anatomy and histochemistry of M. peruviana are described for the first time, highlighting morphoanatomical and histochemical characteristics that act as key adaptations to xeric environmental conditions. [ABSTRACT FROM AUTHOR]

Pseudomonas simiae WCS417 is a plant growth-promoting rhizobacterium that improves plant health and development. In this study, we investigate the early leaf responses of Arabidopsis thaliana to WCS417 exposure and the possible involvement of formate dehydrogenase (FDH) in such responses. In vitro-grown A. thaliana seedlings expressing an FDH::GUS reporter show a significant increase in FDH promoter activity in their roots and shoots after 7 days of indirect exposure (without contact) to WCS417. After root exposure to WCS417, the leaves of FDH::GUS plants grown in the soil also show an increased FDH promoter activity in hydathodes. To elucidate early foliar responses to WCS417 as well as FDH involvement, the roots of A. thaliana wild-type Col and atfdh1-5 knock-out mutant plants grown in soil were exposed to WCS417, and proteins from rosette leaves were subjected to proteomic analysis. The results reveal that chloroplasts, in particular several components of the photosystems PSI and PSII, as well as members of the glutathione S -transferase family, are among the early targets of the metabolic changes induced by WCS417. Taken together, the alterations in the foliar proteome, as observed in the atfdh1 - 5 mutant, especially after exposure to WCS417 and involving stress-responsive genes, suggest that FDH is a node in the early events triggered by the interactions between A. thaliana and the rhizobacterium WCS417. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license., Competing Interests: The author(s) declare no conflict of interest.

A taxonomic treatment for the 17 species of Elaphoglossum sect. Setosa found in Brazil is presented. The species of this section are recognized by the presence of subulate scales and hydathodes on adult leaves, or if hydathodes apparently absent, the leaves less than 10 cm long and spathulate. Several species are also characterized by the presence of minute glandular hairs on petioles and laminae. In Brazil, the group is most diverse in the mountains of southeastern Brazil, where the species grow in a variety of habitats, from deeply shaded riverbeds to partially sunny road banks. Elaphoglossum boragineum, E. brachyneuron, E. eximium and E. hieracioides are first records for the country, some of these known from only one or two collections made on mountains in northern Brazil. Additionally, misapplied names that have long been used in the literature and herbarium specimens, such as E. aubertii, E. jamesonii, E. plumieri, E. spatulatum, and E villosum are here excluded from the Brazilian flora. We provide identification keys, descriptions, synonyms, comments, line drawings, spore images, distribution maps, and an index of herbarium vouchers to all species accepted in this treatment. Lectotypes are designated for Acrostichum alpestre, A. boragineum, and A. tenellum. A neotype is designated for A. horridulum. [ABSTRACT FROM AUTHOR]

Pteris vittata, a fern able to hyperaccumulate arsenic (As) in its fronds, has been object of a number of studies aimed to understand the mechanisms involved in As absorption and tolerance. This study has focused on a new mechanism, As leaching, already observed inP. vittata, but not explained, based on the possible involvement of hydathodes, not yet described in this fern; moreover, the results contained in this article will provide information on a more detailed frond anatomy ofP. vittata. A combination of light and electron microscopic techniques (transmission electron microscopy and environmental scanning electron microscopy with energy dispersive X-ray) and chemical analyses (inductively coupled plasma atomic emission spectroscopy) was used. The results suggest that in phytoremediation processes under field conditions there could be the need to know the atmospheric conditions before harvesting plants, to avoid the loss of As in the environment. [ABSTRACT FROM PUBLISHER]

Sixty-seven coalified compression specimens of leaves, one attached to a stem, have been found in the St. Mary River Formation (uppermost Campanian–lowermost Maastrichtian, Upper Cretaceous) near Cardston, Alberta, Canada. Leaves have long multi-veined petioles with clasping bases, and an ellipsoid to obovate lamina with a convex to almost flat apex, and a crenate margin with one order of convex-convex chloranthoid teeth with angular sinuses. Tooth apices often end in a small concavity interpreted as a hydathode. Several primary veins enter the lamina in a flabellate manner. The central primary vein branches pinnately while lateral primaries, dichotomize toward the margin producing a reticulodromous pattern of secondaries. Secondaries arising from the lateral primary veins are the result of consistent dichotomies and anastomoses with a concurrent loss of gauge. Tertiary veins are alternate percurrent, and quaternaries form an irregular reticulate fabric. Quaternary veins form polygonal areoles with freely ending veinlets. Some specimens show a polygonal pattern of sub-epidermal aerenchyma like that of many other aquatics. Plants are compared to other fossil aquatic taxa, including those from the St. Mary River Formation and extant members of Ranunculaceae, Menyanthaceae and Nymphaeaceae. The specimens are described as a new amphibious aquatic: Zlatkovia crenulata Rothwell & Stockey gen. et sp. nov., eudicot family incertae sedis. This assemblage meaningfully enriches our understanding of aquatic and adjacent wetland habitats near the close of the Cretaceous, and emphasizes that the structure of modern wetland communities was well established before the end of the Mesozoic. [ABSTRACT FROM AUTHOR]

We used lanthanum nitrate as an apoplastic tracer to examine possible mechanisms of retrieval nutrient in the epithem of laminar hydathodes of Ficus formosana Maxim. Cytochemical data showed that vesicles, of constant size about 100 nm, containing the precipitation of lanthanum were present in the cytoplasm and pericytoplasm. These lanthanum-containing vesicles were associated with the elongated profiles of endoplasmic reticulum (ER). Lanthanum deposits were also observed in other organelles such as mitochondria and peroxisomes. Lanthanum nitrate, an apoplastic tracer, can't penetrate the plasmalemma hence its distribution in the vesicles was via endocytosis. In particular, we found that lanthanum precipitation was not present in the plasmolemmasomes, which are the structures of the fluid-phase endocytosis of plasmalemma. From SEM/EDX results, we proposed that the lanthanum ion (La3+) or calcium ion (Ca2+) was absorbed and transported into cell by the coated vesicles endocytosis, not through the fluid-phase endocytosis. The coated vesicle endocytosis, a selective pathway, is a possible mechanism for the uptake of metal ions, which then are further transported into other organelles. [ABSTRACT FROM AUTHOR]

The survival of all plants depends on their abilities to obtain, retain and transport a variety of substances into, through, and out of their bodies. Guttation is one of these abilities to exude fluids out of leaves in the form of droplets through special structures called "hydathodes." These hydathodes are principally located at the tips and margins or edges of the leaves. Guttation is a biophysicochemical and physiological phenomenon in plants which is often noticed in the early morning in a wide range of plant species including angiosperms, gymnosperms, algae, and fungi. The water droplets exuded by guttation contain both the organic and inorganic substances including microorganisms and trickle down from the exuding sites bathing the soil surface and plant residues lying underneath. The main physiological roles of guttation consisting of essentially xylem and phloem saps driven by root pressure involve the transport of water, nutrients, metabolites, hormones, enzymes, transport proteins, pathogenesis-related proteins, etc. within the plants impacting their growth, development, biological, and economic yield. Thus, it serves a variety of purposes in plants. It may also serve as valve for release of excess hydrostatic pressure. Guttation has been shown to play a crucial role in controlling leaf senescence and photosynthesis. Its intensity has been found to be an indicator of root activity. The role of hydathodes has been suggested to be crucial in maintaining water status of plants enabling them survive and grow under water-limited situations. The guttation fluids have tendency to enrich soil fertility and improve its biochemistry by adding and activating certain enzymes such as peroxidases which catalyze the oxidative cross-linking and polymerization of certain organic compounds by hydrogen peroxide and other organic peroxides. The exudation of certain compounds having natural herbicidal effect on other plants helps exercise control over ecological balance among plant communities. Further, it may also serve as a noninvasive assessment test for pesticide residues in plants facilitating proper plant protection measures. It is of great significance that guttation is a means of excreting excess of harmful elements such as Ni, Se, etc. from metal-enriched soils thereby promoting plant growth on such inhospitable soils. Of particular interest is the fact that the variation in color of guttation fluids caused by the presence of different species of fungi therein provides a useful tool for taxonomic classification of certain fungi. Though guttation fluids are considered to be an ideal habitat for pathogen development causing some diseases however, they also contain antimicrobial phylloplane proteins that not only protect plants from certain diseases, they rather elevate disease resistance of certain field crops as well. Guttation fluids may also be used for the production of pharmaceuticals by transgenic plants. However, nutrient losses through guttation at times may be of sufficient magnitude to alter markedly the behavior of the plant. Taken all together, it may be summarized that guttation may be viewed as an efficient barometer for gauging internal chemical strategies translating into increased plant growth, development, and productivity. [ABSTRACT FROM AUTHOR]

The digestive organs of carnivorous plants have external (abaxial) glands and trichomes, which perform various functions. Dionaea muscipula Ellis (the Venus flytrap) is a model carnivorous plant species whose traps are covered by external trichomes. The aim of the study was to fill in the gap regarding the structure of the stellate outer trichomes and their immunocytochemistry and to determine whether these data support the suggestions of other authors about the roles of these trichomes. Light and electron microscopy was used to show the trichomes' structure. Fluorescence microscopy was used to locate the carbohydrate epitopes that are associated with the major cell wall polysaccharides and glycoproteins. The endodermal cells and internal head cells of the trichomes were differentiated as transfer cells, and this supports the idea that stellate trichomes transport solutes and are not only tomentose-like trichomes. Trichome cells differ in the composition of their cell walls, e.g., the cell walls of the internal head cells are enriched with arabinogalactan proteins (AGPs). The cell walls of the outer head cells are poor in both low and highly homogalacturonans (HGs), but the immature trichomes are rich in the pectic polysaccharide (1-4)-β-D-galactan. In the immature traps, young stellate trichomes produce mucilage which may protect the trap surface, and in particular, the trap entrance. However, the role of these trichomes is different when the outer head cells collapse. In the internal head cells, a thick secondary wall cell was deposited, which together with the thick cell walls of the outer head cells played the role of a large apoplastic space. This may suggest that mature stellate trichomes might function as hydathodes, but this should be experimentally proven.

The ecophysiological function(s) and consequences of guttation, a phenomenon by which water is exuded by and accumulated as droplets along the leaf margins under high humidity in many plants that grow in wet soil, has been poorly studied and remains largely unknown. Thus, leaf gas exchange and chlorophyll fluorescence were examined, using two experimental approaches, in Alchemilla mollis plants under conditions that promoted guttation and those that prevented this phenomenon. Although results were variable, depending on the experimental approach, prevention of guttation effected reductions in photosynthesis and transpiration, as well as photochemical activity measured with fluorescence techniques. These findings lend partial support for a previously hypothesized function of guttation: prevention of excess water in leaves, yet they contradict those of several other studies. More work is required in order to adequately understand the function of guttation. [ABSTRACT FROM AUTHOR]

The species delimitation of Lemmaphyllum, including the former segregated Lepidogrammitis in China, was considered as unresolved. Previous treatments accepted between one and 20 species. In the present study, multivariate analysis and maximum parsimony analyses were carried out on data from herbarium specimens of this genus by evaluating 24 quantitative characters and 13 qualitative characters. In total, 558 specimens representing 11 previously accepted species and one variety in China were studied. As a result, three species and two varieties were recognized, Lemmaphyllum pyriforme, L. rostratum, L. carnosum, L. carnosum var. microphyllum, and L. carnosum var. drymoglossoides. Two new combinations and seven new synonyms were introduced. An identification key and distribution maps were provided. This study also elucidated the diagnostic value of two previously ignored characters, scales at the base of stipe and laminae hydathodes. [ABSTRACT FROM AUTHOR]

Aldama arenaria (Baker) E.E.Schill. & Panero and Aldama robusta (Gardner) E.E.Schill. & Panero are aromatic plants, morphologically very similar and usually confused on the analysis of exsiccates. The present study aimed to identify the secretory structures present in vegetative organs and to survey for anatomical features with diagnostic value between A. arenaria and A. robusta based on an examination of these organs. Aldama arenaria and A. robusta exhibit hydathodes in the dentate ornamentations of the leaf margins and apices in addition to glandular trichomes, secretory cavities and ducts, all of which vary with respect to type and location in each species. Xylopodia and adventitious roots constitute the underground system. The xylopodium is covered by epidermis or by suberised cells resulting from periclinal divisions of parenchyma cells. The tuberisation process of adventitious roots results mainly from hypertrophy and hyperplasia of medullary cells, especially in A. arenaria. Through anatomical analysis, useful features for distinction between A. arenaria and A. robusta in exsiccates and fresh materials were identified, and these features were related mainly to the position and frequency of secretory structures. [ABSTRACT FROM AUTHOR]

Guttation is one of the most conspicuous visible phenomena in plants occurring in a wide range of plants. The guttation fluids, though look clear and translucent, carry a number of organic and inorganic constituents. The organic component may include sugars, amino acids, general proteins, antimicrobial phylloplane proteins, transport proteins for transporting sucrose, purine and cytokinins, toxic elements etc. and enzymes such as peroxidases, dehydrogenases, ATPases, in addition to mRNA, ATP, reductants and other important ingredients of plant life. Guttation fluids also contain a number of natural plant hormones such as auxins, gibberellins, cytokinins, abscisic acid etc., apart from several vitamins. Recent discoveries have revealed the presence of a number of salts, ions, nutrients and macromolecules in guttation fluid playing significant role in enhancing disease resistance, tolerance to toxic elements, photosynthetic efficiency, biomass production and economic yield of agricultural crops. In the light of aforementioned discoveries in guttation transgenic plants have been created to serve as bio-factories for producing various kinds of phytochemicals of immense agricultural, pharmaceutical, nutriceutical, therapeutic, cosmeceutic and commercial significance impacting food productivity and human health adding happiness to life. [ABSTRACT FROM AUTHOR]

ABSTRACT Boron (B) is known to accumulate in the leaf margins of different plant species, arguably a passive consequence of enhanced transpiration at the ends of the vascular system. However, transpiration rate is not the only factor affecting ion distribution. We examine an alternative hypothesis, suggesting the participation of the leaf bundle sheath in controlling radial water and solute transport from the xylem to the mesophyll in analogy to the root endodermis. In banana, excess B that remains confined to the vascular system is effectively disposed of via dissolution in the guttation fluid; therefore, impairing guttation should aggravate B damage to the leaf margins. Banana plants were subjected to increasing B concentrations. Guttation rates were manipulated by imposing a moderate osmotic stress. Guttation fluid was collected and analysed continuously. The distribution of ions across the lamina was determined. Impairing guttation indeed led to increased B damage to the leaf margins. The kinetics of ion concentration in guttation samples revealed major differences between ion species, corresponding to their distribution in the lamina dry matter. We provide evidence that the distribution pattern of B and other ions across banana leaves depends on active filtration of the transpiration stream and on guttation. [ABSTRACT FROM AUTHOR]

Since the first collection in 1910, botanists have recognized Sarcopilea (Urticaceae) as a dramatic example of con-vergence with succulent woody members of Crassulaceae. Phylogenetic analyses based on nuclear ribosomal DNA ITS and the trnL-F non-coding plastid DNA regions place Sarcopilea in a Neotropical clade of Pilea. A study of the cystolith, pollen and achene morphology, and of hydathode, hydrenchyma, and stornata position was also performed, confirming the molecular results. Across Rosales, leaf succulence is restricted to the genera Pilea and Sarcopilea. Furthermore, all succulent species of Pilea have an abaxial water-storage hydrenchyma layer in their leaves, a condition unique to the genus. The conditions of adaxial stornata (epistomatic, hyperstomatic), as well as hydathodes restricted to the submarginal abaxial leaf surface, were found in all Neotropical leaf-succulent species. Carbon isotope-ratio mass spectroscopy shows Sarcopilea to have C3 photo-synthesis, therefore Crassulacean acid metabolism is still unknown in Rosales. The impact of molecular systematics of Carib-bean endemic genera is discussed. In light of the new phylogenetic placement of Sarcopilea, a replacement name is provided (Pilea fairchildiana). [ABSTRACT FROM AUTHOR]

Abstract: The leaves, flower and stems of the southern African angiosperm resurrection plant Myrothamnus flabellifolia were investigated at the ultrastructural level to determine the source of previously reported fungal contamination. Fungal mycelia and hyphae of the genera Aspergillus and Penicillium were found localized to the hydathodes of the leaves and stigmatic surfaces of the female flowers in both desiccated and hydrated specimens. A waxy bacterium of the genus Bacillus was found to colonise the waxy epidermal surfaces of the leaves and flowers which was also where fungal cells were found to be absent. It is suggested that the wax like deposits within the leaves and stems as well as over the epidermal surface prevent the growth of the fungal organisms. These fungi opportunistically invade moist surfaces, such as the floral stigmas, during periods of moisture availability and may thus negatively impact plant development. [Copyright &y& Elsevier]

Guttation is a physiological phenomenon resulting in oozing of drops of xylem sap on the tips or edges of leaves of some vascular plants. Of 11 species belonging to different botanical families, only rice (Oryza sativa L.) was found to guttate heavily. Therefore, the process of guttation in rice was studied in depth. Guttation was found to occur from margins, tips, adaxial and abaxial surfaces of leaves. It was the leaf margins that exuded most (151 μl), followed by adaxial surface (135 μl), and tips (98 μl), in that order. Further, the “ridged” portions exuded more fluid than “smooth” portions of the same leaf blade. The rate of guttation was 132 μl at anthesis, 120 μl at tillering, 112 μl at heading and milky stages, and 42 μl at dough stage. The wind velocity and soil moisture stress, as external factors, played dominant roles in the regulation of guttation. Genotypic variability existed for guttation among six cultivars, with cv. NDRH-2 registering the highest value of 110 μl and Mahsuri the lowest (62 μl). The guttational rates exhibited by various cultivars were positively correlated with their panicle weights, i.e., the yield sink capacity, which may be used as a selection criterion for breeding for enhanced yield. These findings on various aspects of guttation in rice are novel. The information should be useful to breeders for creating a new efficient rice plant having altered genetic makeup for increased guttation for yield improvement. [ABSTRACT FROM AUTHOR]

A study of inflorescence and flower development in 12 species from four of the six subgenera of Gunnera (Gunneraceae) was carried out. In the species of subgenus Panke, initiation of floral apices along the partial inflorescences is acropetal but ends up in the late formation of a terminal flower, forming a cyme at maturity. The terminal flower is the largest and the most complete in terms of merosity and number of whorls and thus it is the most diagnostic in terms of species-level taxonomy. The lateral flowers undergo a basipetal gradient of organ reduction along the inflorescence, ranging from bisexual flowers (towards the distal region) to functionally (i.e. with staminodia) and structurally female flowers (towards the proximal region). Our results show that the terminal structure in Gunnera is a flower rather than a pseudanthium. The terminal flower is disymmetric, dimerous and bisexual, representing the common bauplan for Gunnera flowers. It has a differentiated perianth with two sepals and two alternate petals, the latter opposite the stamens and carpels. Comparisons with other members of the core eudicots with labile floral construction are addressed. We propose vegetative and floral putative synapomorphies for the sister-group relationship between Gunneraceae and Myrothamnaceae. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160, 262–283. [ABSTRACT FROM AUTHOR]

The vase life of 26 anthurium (Anthurium andraeanum Hort.) cultivars was evaluated in three separate trials. In the first trial, the influence of 12 morphophysiological characteristics of the cut flower on vase life was investigated. Of these, only spathe color and abaxial stomatal density were able to accurately predict vase life. A vase life prediction equation based on abaxial stomatal density, green/not green and white/not white was able to explain the cultivar variation in vase life in two separate trials conducted over two seasons. The equation was further validated using a different set of anthurium cultivars. Although vase life varied over seasons, the relative ranking of cultivars was similar as indicated by joint regression analysis. Changes in vase life over season were mediated through changes in stomatal density. Time to spadix necrosis was the only senescence indicator that occurred in all cultivars and was highly correlated to vase life determined by a complex criterion in all trials. Time to spadix necrosis is therefore suggested as a simplified criterion for vase life assessment. The possible mechanism for vase life deterioration and an approach to improving vase life in anthurium is discussed. [ABSTRACT FROM AUTHOR]

The leaf teeth glands in four taxa from Salicaceae and six from ‘Flacourtiaceae’ were examined using both light and scanning electron microscopes. There appears to be a progression from glands of simple structure in the flacourtiaceous taxa and a tendency to a more complicated development in morphology and anatomy of the salicaceous species. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 241–256. [ABSTRACT FROM AUTHOR]

Why the leaves of cold temperate deciduous and moisture-loving angiosperms are so often toothed has long puzzled biologists because the functional consequences of teeth remain poorly understood. Here we provide functional and structural evidence that marginal leaf teeth of Chloranthus japonicus, an understory herb, enable the release of guttation sap during root pressure. When guttation from teeth hydathodes was experimentally blocked, we found that the leaf intercellular airspaces became flooded. Measurements of chlorophyll a fluorescence revealed that internal flooding resulted in an inhibition of photosynthesis, most likely through the formation of a film of water within the leaf that reduced CO2 diffusion. Comparing a developmental series of leaves with and without teeth experimentally covered with wax, we found that teeth did not affect overall leaf stomatal conductance and CO2 uptake. However, maximal and effective light-saturation PSII quantum yields of teeth were found to be lower or equal to the surrounding lamina throughout leaf ontogeny. Collectively, our results suggest hydathodes and their development on teeth apices enable the avoidance of mesophyll flooding by root pressure. We discuss how these new findings bear on the potential physiological interpretations of models that apply leaf marginal traits to infer ancient climates. [ABSTRACT FROM AUTHOR]

• The epiphytic species of Campyloneurum have the largest number of layers in theinner cortex of the root. • In Campyloneurum the nectary presence on the petioles and lamines is frequent. • The meristelas number is a taxonomy character relevant for Campyloneurum. Anatomical characters of the sporophyte of five Campyloneurum species are presented: C. aglaolepis, C. angustifolium, C. angustipaletum, C. lorentzii , and C. tucumanense , to evaluate anatomical characters with a taxonomic value. Histological sections of the root, rhizome, and petiole were made in three sections (basal, middle, and distal) and lamina, using specimens of herbarium and material collected for this purpose. Observations were made with a light microscope and a scanning electron microscope. The anatomical characters, such as the type of helical thickening in parenchymal cells in outer cortex and the number of layers in the inner cortex of the root; diameter, presence of prurine, number of meristeles and sclereid nests in the rhizome; adaxial groove and the number of vascular bundles in the petiole; and mesophyll, stomata and hairs types in the lamina, shows a highly significant in taxonomic value for the separation between the five studied species. For the first time, hydathodes, nectaries, diacytic stomatal types and homogeneous mesophyll are described in Campyloneurum , and the anatomy of C. tucumanense is presented. [ABSTRACT FROM AUTHOR]

Changes of view on the course of the transpiration stream beyond the veins in leaves are followed from the imbibition theory of Sachs, through the (symplastic) endosmotic theory of Pfeffer (which prevailed almost unquestioned until the late 1930's), to Strugger's experiments with fluorescent dye tracers and the epifluorescence microscope. This latter work persuaded many to return to the apoplastic-(wall)-path viewpoint which, despite early and late criticisms that were never rebutted, is still widely held. Tracer experiments of the same kind are still frequently published without consideration of the evidence that they do not reveal the paths of water movement. Experiments on rehydration kinetics of leaves have not produced unequivocal evidence for either path. The detailed destinies of the solutes that reach the leaf in the transpiration stream have received little attention. Consideration of physical principles governing flow and evaporation in a transpiring leaf emphasizes that: (1) Diffusion over interveinal distances at the rates in water will account for substantial solute movement in a few minutes, even in the absence of flow. (2) Diffusion can occur also against opposing flow. (3) Volume fluxes in veins are determined by the diameter of the largest vessels, and all the leaves examined contain high conductance supply veins which are tapped into by low-conductance distributing veins. (4) Edges and teeth of leaves will be places of especially rapid evaporation, and they often have high-conductance veins leading to them. (5) Solutes in the stream will tend to accumulate at leaf margins. On the basis of recent work, the view is maintained that the water of the stream enters the symplast through cell membranes very close to tracheary elements. Also, that this occurs locally over a small area of membrane. Many solutes in the stream are left outside in the apoplast. [ABSTRACT FROM AUTHOR]

The TGA genes encode a family of basic domain-leucine zipper (bZIP) transcription factors that are conserved in higher plants. We have continued to unravel the complexity of this gene family by using a polymerase chain reaction (PCR)-based approach. Taking advantage of the conserved amino acid sequence in the bZIP domain found in all members of this gene family, two degenerate oligonucleotides were synthesized based on the sequence of this region in order to amplify by PCR the analogous genomic fragments from the various TGA loci in Arabidopsis. This approach has led us to the finding of a new member of the TGA gene family, and subsequently the isolation of a gene designated as TGA6. Further characterization of the TGA6 locus confirmed our prediction that the gene structure of this family is remarkably conserved. Genomic Southern blot analysis revealed that TGA6 is a single-copy gene in Arabidopsis. Based on the genomic sequence information, gene-specific primers were synthesized for isolating the cDNA that corresponds to the coding region. Subsequently, the cDNA for TGA6 was cloned and sequenced. Gel mobility shift assays with in vitro translated TGA6 protein showed that TGA6 is more like TGA5 in terms of its in vitro DNA-binding properties. The expression of TGA6 in different tissues was estimated by using reverse transcriptase (RT)-PCR and further analyzed in transgenic Arabidopsis lines expressing a TGA6 promoter-GUS fusion. TGA6 promoter activity is found primarily in roots of young seedlings. As seedlings develop, TGA6 is expressed in aging cotyledons, mesophyll cells of hydathodes on leaf margins, vascular tissue and trichomes of senescing rosette leaves, but is very low in primary roots of mature plants. High levels of expression persist in young lateral roots and in regions of the primary root where lateral roots are emerging. In flowers, the activity is localized predominantly to mature pollen grains. The expression pattern of TGA6 reported here is strikingly similar to that of an Arabidopsis acidic chitinase gene. Possible biological significance of TGA6 in cellular defense against pathogens and abiotic stress is discussed. [ABSTRACT FROM AUTHOR]

Laminar hydathodes are known from only three dicot families. In Urticaceae they are associated with minor vein junctions in all five tribes, as surveyed from cleared leaves of 43 species in 30 genera. Only one species lacked hydathodes. Exclusively adaxial hydathodes were found in 28 genera. In tribe Elatostemeae, laminar hydathodes in Pilea and Pellionia species are abaxial, adaxial, or on both surfaces. Guttation was observed in four species. Urtica dioica (adaxial) and Pilea pumila (abaxial) were studied anatomically in detail. Hydathodes in the former have normal bundle structure but xylem gaps sometimes occur. In the latter, phloem is displaced in three previously undescribed ways: 1) ends abruptly near hydathode, 2) curves into connecting vein at adjacent junction, or 3) departs xylem, skirts hydathode independently, and rejoins adjacent xylem strand. Laminar hydathodes are a unifying character of the Urticaceae, and they also strengthen its close relationship to the Moraceae. [ABSTRACT FROM AUTHOR]

Formate dehydrogenase (FDH) catalyzes the conversion of formate (HCOO−) into carbon dioxide (CO 2), coupled with the reduction of NAD+ to NADH. FDH involvement in the response against abiotic stress is well established whereas FDH role against pathogen attack is less known. Therefore, the in silico correlation analysis of the FDH transcript with a biotic stress dataset was performed, which highlighted correlation with genes involved in the response against pathogen attack. Next, a reduction in the expression of an FDH reporter construct in the hydathodes of Arabidopsis thaliana leaves infected with Xanthomonas campestris pv campestris (Xcc) was observed. We also observed an increased proliferation of Xcc in the hydathodes of an atfdh1-5 mutant during the early stages of infection, which further supports FDH involvement in an early defense response activated in the hydathodes upon Xcc infection, possibly through modulation of formate levels. • Plant Formate dehydrogenase catalyzes the conversion of formate into carbon dioxide. • Expression of A. thaliana FDH-encoding gene correlates with genes involved in plant defense responses. • FDH promoter activity is reduced, in the hydathodes, upon infection with Xanthomonas campestris campestris Xcc. • Spread of Xcc through hydathodes is enhanced in atfdh1-5 mutant. • We propose formate as signaling molecule during early plant response against Xcc. [ABSTRACT FROM AUTHOR]

Xanthomonas campestris pv. campestris (Xcc) causes the devastating disease Black rot in Brassicaceae. Typically Xcc enters the plant through specialized organs on the leaf margin, called hydathodes, and spreads from there through the vasculature. In order to mimic natural entry as closely as possible, we here describe a "hydathode guttation"-based entry assay for Xcc in Arabidopsis. This disease assay combines spray inoculation with the induction of guttation and allows reabsorption of guttation droplets by the plant. Moreover, our assay relies on a bioluminescent reporter strain of Xcc to allow direct visualization of both entry and subsequent spreading of Xcc in its host. The assay allows the routine infection from one to two hydathodes per Arabidopsis leaf. Infections are scored 14 days post inoculation, just before the infection goes systemic.