The Plant Cuticle: An Ancient Guardian Barrier Set Against Long-Standing Rivals

The aerial surfaces of plants are covered by a protective barrier formed by the cutin polyester and waxes, collectively referred to as the cuticle. Plant cuticles prevent the loss of water, regulate transpiration, and facilitate the transport of gases and solutes. As the cuticle covers the outermost epidermal cell layer, it also acts as the first line of defense against environmental cues and biotic stresses triggered by a large array of pathogens and pests, such as fungi, bacteria, and insects. Numerous studies highlight the cuticle interface as the site of complex molecular interactions between plants and pathogens. Here, we outline the multidimensional roles of cuticle-derived components, namely, epicuticular waxes and cutin monomers, during plant interactions with pathogenic fungi. We describe how certain wax components affect various pre-penetration and infection processes of fungi with different lifestyles, and then shift our focus to the roles played by the cutin monomers that are released from the cuticle owing to the activity of fungal cutinases during the early stages of infection. We discuss how cutin monomers can activate fungal cutinases and initiate the formation of infection organs, the significant impacts of cuticle defects on the nature of plant–fungal interactions, along with the possible mechanisms raised thus far in the debate on how host plants perceive cutin monomers and/or cuticle defects to elicit defense responses.

Structural dermis remodeling in a skin expansion rat model

Introduction. Skin expansion is known to be the most effective way to obtain skin for alloplastic closing of large defects, and it has proven to be successfully used in various fields of surgery, cosmetology, and traumatology. At the same time, the issues of skin flap restructuring when it is stretched and possible range of its application are still relevant. In this regard, the aim was to study the adaptive skin rearrangements of the fibrous skeleton in a murine skin expansion model. Materials and methods. We used the skin of mature male Wistar rats (N=30) after a 2-week stretching. We utilized a complex morphological light and electron microscopy approach as well as an immunohistochemi-cal method to determine the types of collagen and to study the alterations in skin samples. Results. We revealed pronounced reactive changes in the skin structural components in the skin expansion area. On day 14, we observed a decrease in the epidermal cell layer thickness as well as stretching, partial disorganization, and damage of dermal fibrous structure. At the same time, cellular mechanisms of regen-eration and activation of collagen synthesis were launched, the morphological substrate of which was (1) a significant 2.7-fold increase in the number density of fibroblasts, which produce substances for building fibrous structures, (2) a five-fold increase in macrophages, which are a catalyst for the fibroblast functional activity and (3) a collagen fiber types’ redistribution s with Type III collagen structures’ predominance. Conclusion. The results indicate, first of all, the restructuring of the dermal fibrous component, which im-plies reparative and restorative processes. These must be taken into account in clinical practice to achieve not only an esthetic effect but also the subsequent adequate functioning and vital activity of the skin flap. Keywords: skin expansion, fibrous dermis, remodeling, skin, hyperextension

SAW homeodomain transcription factors regulate initiation of leaf margin serrations

Plant leaves are the main photosynthetic organ of plants and they occur in an array of different shapes. Leaf shape is determined by morphogenesis whereby patterning of the leaf margin can result in interspaced leaf serrations, lobes, or leaflets, depending on the species, developmental stage, and in some instances the environment. In Arabidopsis, mutations in the homeodomain transcription factors SAW1 and SAW2 result in more prominent leaf margin serrations. Here we show that serrations appear precociously in the saw1 saw2 mutant. The pattern of auxin maxima, and of PIN1 and CUC2 expression, which form a feedback loop that drives serration outgrowth, is altered in saw1 saw2 and correlates with precocious serration initiation. SAW1 is not expressed in the outer epidermal cell layer where PIN1 convergence points generate auxin maxima. Instead, SAW1 is expressed on the adaxial side of the leaf and expression in this domain is sufficient for function. We suggest that SAW1 and SAW2 repress serration initiation and outgrowth by promoting the transition to a determinate fate in the leaf margin.

An epidermis-driven mechanism positions and scales stem cell niches in plants

How molecular patterning scales to organ size is highly debated in developmental biology. We explore this question for the characteristic gene expression domains of the plant stem cell niche residing in the shoot apical meristem. We show that a combination of signals originating from the epidermal cell layer can correctly pattern the key gene expression domains and notably leads to adaptive scaling of these domains to the size of the tissue. Using live imaging, we experimentally confirm this prediction. The identified mechanism is also sufficient to explain de novo stem cell niches in emerging flowers. Our findings suggest that the deformation of the tissue transposes meristem geometry into an instructive scaling and positional input for the apical plant stem cell niche.

Immunohistochemical Study of Transforming Growth Factor-α Expression in Normal and Perforated Tympanic Membrane

An immunohistochemical study of transforming growth factor-α (TGF-α) distribution was carried out to clarify the mechanism responsible for accelerated epidermal cell proliferation after perforation of the rabbit tympanic membrane. In the normal tympanic membrane, TGF-α expression was not observed, whereas after perforation, over the whole tympanic membrane including the margin of the perforation, TGF-α-positive cells appeared and were scattered in the epidermal cell layer. After healing of the perforation, a marked decrease of TGF-α-positive cells in the tympanic membrane was observed. This finding suggests that TGF-α induces proliferation of epidermal cells after the perforation stimulus.

Differential Expression of Chitinase and ß-1,3-Glucanase Genes in Various Tissues of Potato Plants

We have analyzed the tissue-specific expression of chitinase, β-1,3-glucanase and, for com parison, phenylalanine ammonia-lyase genes in healthy, unstressed potato (Solanum tuberosum) plants by using RNA -RNA hybridization and immunostaining techniques to localize the respective mRNAs and proteins in situ. Preparations of leaf, flower, shoot tip, node and axillary bud revealed that chitinase exhibited a distinctive and characteristic expression pattern in being confined to the epidermal cell layer, while β-1,3-glucanase and phenylalanine ammonia-lyase were present to varying extents in most tissues of these organs. These distinctive patterns of expression suggest fundamentally different roles for the two glucanohydrolases in the metabolism of unstressed plants

Characterization of red alder ectomycorrhizae: a preface to monitoring belowground ecological responses

Critical ecological research on belowground ecosystems has often been impeded because of the inability to adequately recognize ectomycorrhizal relationships, especially the abundance, diversity, and distribution of the fungus component, and the specificity of particular fungus–host combinations. Red alder, with its high degree of host specificity and paucity of fungal symbionts, provides an ideal model for studying these attributes. Eleven morphologically recognizable types of ectomycorrhizae were characterized from field-collected root material, greenhouse soil bioassays, and laboratory syntheses. Most mycobionts were basidiomycetes, as evidenced by abundant clamp connections present in the mantle and extramatrical hyphae. Seven mycobionts identified to species included Alpova diplophloeus, Thelephora terrestris, Lactarius obscuratus, Cortinarius bibulus, Laccaria laccata, Hebeloma crustuliniforme, and Paxillus involutus. Many of the ectomycorrhizae collected in the field appeared to have more than one mycobiont present in the mantle. Root tips could generally be categorized into either flexuous or succulent morphological types. The flexuous types were long, thin, indeterminate in growth, with an acute root apex, and the mantle and Hartig net in longitudinal section were not well formed near the root apex. The succulent types were short, thick, determinate in growth, with a rounded root apex, and the mantle and Hartig net in longitudinal section were well formed near the root apex. Additional characteristics important in distinguishing among red alder ectomycorrhizal types included color, extent of extramatrical hyphae development, mantle surface characteristics, and selected microchemical reactions. Mantle thickness was highly variable and not useful in characterization. Hartig net development was shallow, and regardless of mycorrhizal origin, rarely extended beyond one epidermal cell layer. Key words: ectomycorrhizae, Alnus, characterization, ecology, belowground.

Alpha-amylase in seed hulls of developing Brassica campestris

Extracts of hulls from developing Brassica campestris and Brassica napus seeds were examined for α-amylase activity. The enzyme was compared with α-amylase from barley pericarp and germinated barley seeds, using isoelectric focusing. Enzymes of similar isoelectric point (pI) were present in B. campestris, B. napus, and barley pericarp. Additional bands of activity were present in B. napus. The major α-amylase component of germinated barley has a high pI, but no corresponding isozyme was detected in the other three samples. The increase in total activity of α-amylase in Brassica seed hulls coincided with the increase in starch granule size in the epidermal cell layer, with maximum activity approximately 16 days after pollination.

The regulation of gene mutation in plants

This discussion is based largely on work on mutable genes in maize by McClintock (1946-68, 1965), Brink and his associates (Barclay & Brink 1952; Brink & Nilan 1952), and Peterson (1966), with some points illustrated by reference to my own studies on Antirrhinum majus in collaboration with B. J. Harrison at the John Innes Institute and G. R. K. Sastry at the University of Leeds. The phenomenon of high mutability is, I believe, likely to have the same basis in Antirrhinum (and in numerous other flowering plants) as in maize. I shall not be dealing with the equally interesting and possibly related phenomenon of paramutation , described by Brink (1964). The mutability we are concerned with is set apart from most gene mutation by its extraordinarily high frequency. One finds alleles at well-known gene loci in both maize and Antirrhinum which mutate thousands of times in the development of every plant carrying them so that, if the gene in question controls pigmentation, numerous differently coloured spots and sectors of various sizes appear throughout the plant. All the examples I shall be mentioning concern anthocyanin pigmentation in the maize seed or in the epidermal cell layer of Antirrhinum. The mutations affect not only these visibly pigmented tissues but also the subepidermal cells, which do not normally form pigment themselves but give rise to germ cells which can transmit an altered capacity for pigment synthesis to the entire plant in the next generation. In some cases the frequency of mutations among the germ cells can amount to several per cent and in our Antirrhinum system we have occasionally encountered frequencies of more than 50 %. We are dealing here with a process which is at least 3 or 4 orders of magnitude more frequent than any reasonable estimate of the general frequency of errors in DNA replication.