Fine structure of isolated and non-isolated potato tuber periderm

Cell walls of the periderm of native potato tuber (Solanum tuberosum L. cv. Primura) consist of a primary wall, a suberized secondary wall and a tertiary wall. With a mixture of pectinase and cellulase intact periderm membranes can be isolated. Isolation does not affect fine structure. It is suggested that the lignin in the middle lamellae and primary walls prevents the enzymes from digesting pectinaceous materials and cellulose. In specimens fixed with OsO₄, the suberized walls appear as alternating electrondense and electron-lucent lamellae. This lamellar architecture is not altered by extraction with chloroform. Therefore, the current view that the electronlucent lamellae consist of soluble lipids (waxes) can no longer be maintained. It is argued that the lamellation is a property of the suberin itself, and the suberized wall consists of alternating layers of suberins differing in polarity. A hypothesis of suberin assembly from sub-units is advanced and the subunits are shown for the first time.     

Electron-microscopic and morphometric study of vesiculation in the epithelial cell layer of the toad urinary bladder

Summary The sequence of events in the establishment of a keratinised epidermis has been related to age and crown rump length in fetal rats. Differentiation of the epidermis occurs under cover of the periderm throughout gestation. Ten stages are defined between 12d intra-uterine life and birth. Membrane-coating granules (MCGs) appeared at 18d (Stage 4) after the appearance of tonofilaments but before the appearance of the first fetal keratohyaline granules (KHGs) at 19d (Stage 5). Measurement of the position of MCGs within the cells showed a less marked concentration near the superficial border of the cells than that found at later stages. As KHGs formed, exocytosis of MCGs occurred into the intercellular space immediately deep to the periderm. It is suggested that after 19d (Stage 5) the periderm serves to retain the contents of the MCGs in this space so providing the permeability barrier and that prior to that stage the periderm itself probably provides the permeability barrier of fetal skin.     

Identification of regulatory elements recapitulating early expression of L-plastin in the zebrafish enveloping layer and embryonic periderm

We have cloned and characterized an intronic fragment of zebrafish lymphocyte cytosolic protein 1 (lcp1, also called L-plastin) that drives expression to the zebrafish enveloping layer (EVL). L-plastin is a calcium-dependent actin-bundling protein belonging to the plastin/fimbrin family of proteins, and is necessary for the proper migration and attachment of several adult cell types, including leukocytes and osteoclasts. However, in zebrafish lcp1 is abundantly expressed much earlier, during differentiation of the EVL. The cells of this epithelial layer migrate collectively, spreading vegetally over the yolk. L-plastin expression persists into the larval periderm, a transient epithelial tissue that forms the first larval skin. This finding establishes that L-plastin is activated in two different embryonic waves, with a distinct regulatory switch between the early EVL and the later leukocyte. To better study L-plastin expressing cells we attempted CRISPR/Cas9 homology-driven recombination (HDR) to insert a self-cleaving peptide (Cre-P2A-EGFP-CAAX) downstream of the native lcp1 promoter. This produced a stable zebrafish line expressing Cre recombinase in EVL nuclei and green fluorescence in EVL cell membranes. In vivo tracking of these labeled cells provided enhanced views of EVL migration behavior, membrane extensions, and mitotic events. Finally, we experimentally dissected key elements of the targeted lcp1 locus, discovering a ∼300 bp intronic sequence sufficient to drive EVL expression. The lcp1: Cre-P2A-EGFP-CAAX zebrafish should be useful for studying enveloping layer specification, gastrulation movements and periderm development in this widely used vertebrate model. In addition, the conserved regulatory sequences we have isolated predict that L-plastin orthologs may have a similar early expression pattern in other vertebrate embryos.     

Simultaneous cell death and desquamation of the embryonic diffusion barrier during epidermal development

The periderm is an epithelial layer covering the emerging epidermis in early embryogenesis of vertebrates. In the chicken embryo, an additional cellular layer, the subperiderm, occurs at later embryonic stages underneath the periderm. The questions arose what is the function of both epithelial layers and, as they are transitory structures, by which mechanism are they removed. By immunocytochemistry, the tight junction (TJ) proteins occludin and claudin-1 were localized in the periderm and in the subperiderm, and sites of close contact between adjacent cells were detected by electron microscopy. Using horseradish peroxidase (HRP) as tracer, these contacts were identified as tight junctions involved in the formation of the embryonic diffusion barrier. This barrier was lost by desquamation at the end of the embryonic period, when the cornified envelope of the emerging epidermis was formed. By TUNEL and DNA ladder assays, we detected simultaneous cell death in the periderm and the subperiderm shortly before hatching. The absence of caspases-3, -6, and -7 activity, key enzymes of apoptosis, and the lack of typical morphological criteria of apoptosis such as cell fragmentation or membrane blebbing point to a special form of programmed cell death (PCD) leading to the desquamation of the embryonic diffusion barrier.     

Wax and suberin development of native and wound periderm of potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) and its relation to peridermal transpiration

Native and wound periderm was isolated enzymatically from potato (Solanum tuberosum L. cv. Desirée) tubers at different time intervals between 0 days up to 4 weeks after harvesting. Wound periderm formation was induced by carefully removing native periderm from freshly harvested tubers before storage. The chemical composition of lipids (waxes) obtained by chloroform extraction, as well as the monomeric composition of native and wound suberin polymer after transesterification by boron trifluoride/methanol, was analyzed using gas chromatography and mass spectrometry. Both types of periderm contained up to 20% extractable lipids. Besides linear long-chain aliphatic wax compounds, alkyl ferulates were detected as significant constituents. In wound periderm they amounted to more than 60% of the total extracts. Within 1 month of storage, suberin amounts in the polymer increased 2-fold in native periderm (180 g cm^–2), whereas in wound periderm about 75.0 g cm^–2 suberin polymer was newly synthesized. Native potato tuber periderm developed a very efficient transport barrier for water with permeances decreasing from 6.4×10^–10 m s^–1 to 5.5×10^–11 m s^–1 within 1 month of storage. However, the water permeability of wound periderm was on average 100 times higher with permeances decreasing from 4.7×10^–8 m s^–1 after 3 days to only 5.4×10^–9 m s^–1 after 1 month of storage, although suberin and wax amounts in wound periderm amounted to about 60% of native periderm. From this result it must be concluded that the occurrence of suberin with wax depositions in cell walls does not necessarily allow us to conclude that these cell walls must be nearly perfect barriers to water transport. In addition to the occurrence of the lipophilic biopolymer suberin and associated waxes, the still unknown molecular arrangement and precisely localized deposition of suberin within the cell wall must contribute to the efficiency of suberin as a barrier to water transport.     

An ultrastructural study of periderm granules in the regenerating feather of the jungle fowl

Summary Periderm granules in the support cells of regenerating feathers of mature male Jungle Fowls were studied ultrastructurally and histochemically. Histochemical results showed the absence of carbohydrate and lipid, and the presence of protein in the periderm granules. The periderm granules were measured at successive levels of feather regeneration. The mean size of the periderm granules increased significantly as the regenerating feather matured, and this observation was suggestive of a storage function, perhaps of surplus or waste protein. The cells in which the periderm granules are found also contain glycogen. There are numerous desmosomal junctions on their interdigitating plasma membranes. These transient cells may collect waste, provide nutrition, and serve as a protective barrier for the definitive cells of the regenerating feather.     

云南紫胶虫八种寄主树次生韧皮部与周皮的解剖

云南紫胶虫８种寄生树的次生韧生皮部轴向系统由筛管、伴胞、韧皮薄壁组织细胞、纤维组成,横向系统为射线。青果榕和久树中分别尚有乳汁和这和分泌组织,滇刺枣与久树中筛板斜到横向,有复筛板,单筛板。蒙自合欢和雨树均具有复筛板,筛板分别为倾斜到横向及倾斜,其余植物的筛板均横向,具单筛板,除蒙自合欢外筛管分子都有Ｐ－蛋白质;除青果榕外筛管分子都具有淀粉。除雨树、宝树、久树外、直径１．５－２．０ｃｍ的小枝条的木拴     

Ultrastructural changes in hatching-gland cells of pike embryos (Esox lucius L.) and evidence for their degeneration by apoptosis

Summary Around hatching, when the pike embryo sheds its acellular egg envelope, marked changes occur in the cellular covering of the embryo. This cellular covering consists of a peridermal layer and a mono-layered presumptive epidermis. The periderm begins to disintegrate shortly before hatching and is sloughed off in the first posthatching period. The cellular covering produces hatching enzyme, the protease that partly dissolves the zona radiata interna of the acellular envelope. By means of the peroxidase-anti-peroxidase staining method with antibodies against hatching enzyme the cells producing this enzyme (hatching gland cells, HGCs) could be identified ultrastructurally. They are interspersed as single cells between the periderm and the presumptive epidermis. The secretory cycle of the HGC was studied. Hatching enzyme is released by an exocytotic secretory process in which multiple secretion into a secretion vacuole predominates. Exocytosis into surrounding intercellular spaces also occurs. These results show that the HGCs are merocrine glands. The HGC also has some holocrine nature, however, in that only a single, massive release of its secretory product occurs. The death of the transitory HGCs in posthatching stages is characterized by condensation of the cell, formation of surface protuberances and splitting up into globular cell fragments. Eventually these fragments are ingested by epidermal cells and digested. These results lead to the conclusion that the pike HGCs degenerate by apoptosis, unlike true holocrine cells.