Species in the genus Utricularia are carnivorous plants that prey on invertebrates using traps of leaf origin. The traps are equipped with numerous different glandular trichomes. Trichomes (quadrifids) produce digestive enzymes and absorb the products of prey digestion. The main aim of this study was to determine whether arabinogalactan proteins (AGPs) occur in the cell wall ingrowths in the quadrifid cells. Antibodies (JIM8, JIM13, JIM14, MAC207, and JIM4) that act against various groups of AGPs were used. AGP localization was determined using immunohistochemistry techniques and immunogold labeling. AGPs localized with the JIM13, JIM8, and JIM14 epitopes occurred in wall ingrowths of the pedestal cell, which may be related to the fact that AGPs regulate the formation of wall ingrowths but also, due to the patterning of the cell wall structure, affect symplastic transport. The presence of AGPs in the cell wall of terminal cells may be related to the presence of wall ingrowths, but processes also involve vesicle trafficking and membrane recycling, in which these proteins participate.

The genus Utricularia (bladderworts) species are carnivorous plants that prey on invertebrates using traps with a high-speed suction mechanism. The outer trap surface is lined by dome-shaped glands responsible for secreting water in active traps. In terminal cells of these glands, the outer wall is differentiated into several layers, and even cell wall ingrowths are covered by new cell wall layers. Due to changes in the cell wall, these glands are excellent models for studying the specialization of cell walls (microdomains). The main aim of this study was to check if different cell wall layers have a different composition. Antibodies against arabinogalactan proteins (AGPs) were used, including JIM8, JIM13, JIM14, MAC207, and JIM4. The localization of the examined compounds was determined using immunohistochemistry techniques and immunogold labeling. Differences in composition were found between the primary cell wall and the cell secondary wall in terminal gland cells. The outermost layer of the cell wall of the terminal cell, which was cuticularized, was devoid of AGPs (JIM8, JIM14). In contrast, the secondary cell wall in terminal cells was rich in AGPs. AGPs localized with the JIM13, JIM8, and JIM14 epitopes occurred in wall ingrowths of pedestal cells. Our research supports the hypothesis of water secretion by the external glands.

Carnivorous plants can survive in poor habitats because they have the ability to attract, capture, and digest prey and absorb animal nutrients using modified organs that are equipped with glands. These glands have terminal cells with permeable cuticles. Cuticular discontinuities allow both secretion and endocytosis. In Drosophyllum lusitanicum, these emergences have glandular cells with cuticular discontinuities in the form of cuticular gaps. In this study, we determined whether these specific cuticular discontinuities were permeable enough to antibodies to show the occurrence of the cell wall polymers in the glands. Scanning transmission electron microscopy was used to show the structure of the cuticle. Fluorescence microscopy revealed the localization of the carbohydrate epitopes that are associated with the major cell wall polysaccharides and glycoproteins. We showed that Drosophyllum leaf epidermal cells have a continuous and well-developed cuticle, which helps the plant inhibit water loss and live in a dry environment. The cuticular gaps only partially allow us to study the composition of cell walls in the glands of Drosophyllum. We recoded arabinogalactan proteins, some homogalacturonans, and hemicelluloses. However, antibody penetration was only limited to the cell wall surface. The localization of the wall components in the cell wall ingrowths was missing. The use of enzymatic digestion improves the labeling of hemicelluloses in Drosophyllum glands.

Carnivorous plants are mixotrophs that have developed the ability to lure, trap, and digest small organisms and utilize components of the digested bodies. Leaves of Drosophyllum lusitanicum have two kinds of glands (emergences): stalked mucilage glands and sessile digestive glands. The stalked mucilage glands perform the primary role in prey lure and trapping. Apart from their role in carnivory, they absorb water condensed from oceanic fog; thus, plants can survive in arid conditions. To better understand the function of carnivorous plant emergences, the molecular composition of their cell walls was investigated using immunocytochemical methods. In this research, Drosophyllum lusitanicum was used as a study system to determine whether cell wall immunocytochemistry differs between the mucilage and digestive glands of other carnivorous plant species. Light and electron microscopy were used to observe gland structure. Fluorescence microscopy revealed the localization of carbohydrate epitopes associated with the major cell wall polysaccharides and glycoproteins. The mucilage gland (emergence) consists of a glandular head, a connecting neck zone, and stalk. The gland head is formed by an outer and inner layer of glandular (secretory) cells and supported by a layer of endodermoid (barrier) cells. The endodermoid cells have contact with a core of spongy tracheids with spiral-shaped thickenings. Lateral tracheids are surrounded by epidermal and parenchymal neck cells. Different patterns of cell wall components were found in the various cell types of the glands. Cell walls of glandular cells generally are poor in both low and highly esterified homogalacturonans (HGs) but enriched with hemicelluloses. Cell walls of inner glandular cells are especially rich in arabinogalactan proteins (AGPs). The cell wall ingrowths in glandular cells are significantly enriched with hemicelluloses and AGPs. In the case of cell wall components, the glandular cells of Drosophyllum lusitanicum mucilage glands are similar to the glandular cells of the digestive glands of Aldrovanda vesiculosa and Dionaea muscipula.

The two-armed bifids (bifid trichomes) occur on the external (abaxial) trap surface, petiole, and stem of the aquatic carnivorous plant Aldrovanda vesiculosa (Droseracee). These trichomes play the role of mucilage trichomes. This study aimed to fill the gap in the literature concerning the immunocytochemistry of the bifid trichomes and compare them with digestive trichomes. Light and electron microscopy was used to show the trichome structure. Fluorescence microscopy revealed the localization of carbohydrate epitopes associated with the major cell wall polysaccharides and glycoproteins. The stalk cells and the basal cells of the trichomes were differentiated as endodermal cells. Cell wall ingrowths occurred in all cell types of the bifid trichomes. Trichome cells differed in the composition of their cell walls. The cell walls of the head cells and stalk cells were enriched with arabinogalactan proteins (AGPs); however, they were generally poor in both low- and highly-esterified homogalacturonans (HGs). The cell walls in the trichome cells were rich in hemicelluloses: xyloglucan and galactoxyloglucan. The cell wall ingrowths in the basal cells were significantly enriched with hemicelluloses. The presence of endodermal cells and transfer cells supports the idea that bifid trichomes actively transport solutes, which are polysaccharide in nature. The presence of AGPs (which are considered plant signaling molecules) in the cell walls in these trichome cells indicates the active and important role of these trichomes in plant function. Future research should focus on the question of how the molecular architecture of trap cell walls changes in cells during trap development and prey capture and digestion in A. vesiculosa and other carnivorous plants.

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.

Carnivorous plants are unique due to their ability to attract small animals or protozoa, retain them in specialized traps, digest them, and absorb nutrients from the dissolved prey material; however, to this end, these plants need a special secretion-digestive system (glands). A common trait of the digestive glands of carnivorous plants is the presence of transfer cells. Using the aquatic carnivorous species Aldrovanda vesiculosa, we showed carnivorous plants as a model for studies of wall ingrowths/transfer cells. We addressed the following questions: Is the cell wall ingrowth composition the same between carnivorous plant glands and other plant system models? Is there a difference in the cell wall ingrowth composition between various types of gland cells (glandular versus endodermoid cells)? Fluorescence microscopy and immunogold electron microscopy were employed to localize carbohydrate epitopes associated with major cell wall polysaccharides and glycoproteins. The cell wall ingrowths were enriched with arabinogalactan proteins (AGPs) localized with the JIM8, JIM13, and JIM14 epitopes. Both methylesterified and de-esterified homogalacturonans (HGs) were absent or weakly present in the wall ingrowths in transfer cells (stalk cells and head cells of the gland). Both the cell walls and the cell wall ingrowths in the transfer cells were rich in hemicelluloses: xyloglucan (LM15) and galactoxyloglucan (LM25). There were differences in the composition between the cell wall ingrowths and the primary cell walls in A. vesiculosa secretory gland cells in the case of the absence or inaccessibility of pectins (JIM5, LM19, JIM7, LM5, LM6 epitopes); thus, the wall ingrowths are specific cell wall microdomains. Even in the same organ (gland), transfer cells may differ in the composition of the cell wall ingrowths (glandular versus endodermoid cells). We found both similarities and differences in the composition of the cell wall ingrowths between the A. vesiculosa transfer cells and transfer cells of other plant species.

The arabinogalactan proteins (AGP) play important roles in plant growth and developmental processes. However, to the best of our knowledge, there is no information on the spatial distribution of AGP in the plant organs and tissues of carnivorous plants during their carnivorous cycle. The Dionaea muscipula trap forms an \"external stomach\" and is equipped with an effective digestive-absorbing system. Because its digestive glands are composed of specialized cells, the hypothesis that their cell walls are also very specialized in terms of their composition (AGP) compared to the cell wall of the trap epidermal and parenchyma cells was tested. Another aim of this study was to determine whether there is a spatio-temporal distribution of the AGP in the digestive glands during the secretory cycle of D. muscipula. Antibodies that act against AGPs, including JIM8, JIM13 and JIM14, were used. The localization of the examined compounds was determined using immunohistochemistry techniques and immunogold labeling. In both the un-fed and fed traps, there was an accumulation of AGP in the cell walls of the gland secretory cells. The epitope, which is recognized by JIM14, was a useful marker of the digestive glands. The secretory cells of the D. muscipula digestive glands are transfer cells and an accumulation of specific AGP was at the site where the cell wall labyrinth occurred. Immunogold labeling confirmed an occurrence of AGP in the cell wall ingrowths. There were differences in the AGP occurrence (labeled with JIM8 and JIM13) in the cell walls of the gland secretory cells between the unfed and fed traps.

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Key sources of information on the nature of early terrestrial ecosystems are the fossilized remains of plants and associated organic encrustations, which are interpreted as either biofilms, biological soil crusts or lichens. The hypothesis that some of these encrustations might be the remains of the thalloid gametophytes of embryophytes provided the stimulus for this investigation. Fossils preserved in charcoal were extracted from Devonian Period (Lochkovian Stage, c. 410-419 Myr old) sediments at a geological site in Shropshire (UK). Scanning electron micrographs (SEMs) of the fossils were compared with new and published SEMs of extant bryophytes and tracheophytes, respectively. One specimen was further prepared and imaged by transmission electron microscopy. Fossils of thalloid morphology were composed almost entirely of cells with labyrinthine ingrowths; these also were present in fossils of axial morphology where they were associated with putative food-conducting cells. Comparison with modern embryophytes demonstrates that these distinctive cells are transfer cells (TCs). Our fossils provide by far the earliest geological evidence of TCs. They also show that some organic encrustations are the remains of thalloid land plants and that these are possibly part of the life cycle of a newly recognized group of plants called the eophytes.