Lower Epidermal Cells Research Articles

UVA Induced Darkening of Lower Epidermal Cells as an in vitro System of Immediate Pigment Darkening (IPD) and Mechanisms of IPD

AbstractImmediate pigment darkening (IPD), which is a skin tanning reaction induced by UVA or visible light irradiation, is generally thought to result from photo oxidation of pre‐existing melanin. Only a few in vitro systems useful for studying the detailed mechanisms have been developed. The purpose of this study is to present UVA‐induced darkening at the cell level in an in vitro system and clarify the mechanisms of IPD.Human lower epidermal cells (LECs) separated by the Percoll density gradient centrifugation and murine B16 malignant melanoma cells (B16Cs) were treated to prepare a melanin containing, pyridine‐insoluble precipitate (PUP). The degree of darkness of the UVA‐exposed cells was expressed as reflectance at 400 nm (RE) from PUP. With increasing UVA dose, the RE from B16C‐PUP induced no significant change, but the RE from LEC‐PUP decreased. Thus the model of UVA‐induced darkening at the cell level using LEC was successful. Measurement of the height of electron spin resonance (ESR) signal from PUPs of whole epidermal cells and of B16Cs revealed a 10% decrease in the former and no significant change in the latter after UVA treatment. These results suggest that a combination of the melanin in intracellular melanosomes and UVA exposure alone did not induce melanin darkening of IPD, and also that the semiquinoid form of melanin monomeric units decreased in the keratinocyte melanin. Taking into consideration the molecular structure of melanin, these results also suggest that photo oxidation of melanin monomeric units from the semiquinoid to the quinoid form is one of the mechanisms of IPD causing the darkening of melanin pigment.

Distribution and mobility of concanavalin A receptors on isolated guinea pig epidermal cells at various stages of differentiation.

Trypsinized guinea pig epidermal cells were separated by velocity sedimentation at unit gravity. Based on the relationship between cell size and both morphological and functional aspects of differentiation, the cells were classified as lower (a diameter less than 12.5 micron), middle (a diameter between 12.5 and 15 micron), and upper (a diameter greater than 15 micron) epidermal cells. Fresh cells exposed to rhodaminated concanavalin A (Con A) were sedimented and reacted with fluoresceinated anti-Con A serum to distinguish cell surface Con A from intracellular lectin. Labeling at 4 degrees C resulted in a uniform surface distribution of Con A irrespective of cell size. After a 1-hr incubation of Con A-labeled cells in lectin-free medium at 37 degrees C, lower epidermal cells and approximately half of middle epidermal cells internalized Con A/receptor complexes by endocytosis while lectin remained diffusely on the remainder of middle epidermal cells and upper epidermal cells. By electron microscopy, ferritin-Con A was clustered on surface areas and invaginations of the plasma membrane before being endocytosed. We concluded that the differentiation of epidermal cells was accompanied by progressive decrease in endocytosis and, most probably, mobility of Con A receptors.

In situ identification, localization and quantification of flavones in petals and green leaves of Silene pratensis grown under different light regimes

Quartz optic microscopy with variable wavelength illumination was used to locate and quantify the ultraviolet absorbing flavone isovitexin 7-0-qlucoside in leaf and petal epidermis in Silene pratensis. Mean vacuolar absorption spectra and mean cell wall thickness were used to estimate flavone contents in different organs. The flavone spectrum in vivo coincides with that found in vitro (absorption peaks at 273 and 335 nm). Flavone concentration in the green leaves is determined by the light levels under which individual plants were raised; with low levels (8,000 lux) a few upper epidermal cells show faint absorption at 335 nm. In plants raised at 18,000 lux, 60-70 % of the upper epidermal cells absorbed at 334 nm and flavone concentration in the absorbing cells was 1-3 mM. In plants raised under high light intensity (36,000 lux), most of the upper epidermal cells absorbed at 335 nm and the flavone concentration in the cells ranged from 8.5 to 15 mM. In the high light intensity plants some lower epidermal cells also absorb at 335 nm (flavone concentrations 2-5 mM). In all plants investigated, nearly all the cells of the upper epidermis of the netals absorb strongly at 335 nm (concentrations exceeding 19 mM).

Accumulation of Cytokinin-Induced Betacyanin in Specific Cells ofAmaranthus tricolorSeedlings

The accumulation of betacyanin, in dark-grown Amaranthus tricolor seedlings, in response to cytokinins or red light, occurs mainly in two specific tissues, the lower epidermal cells of the cotyledons (with the exception of guard cells), and the endodermis of the hypocotyl. The possible significance of this 'spatial pattern of competence' is discussed, together with the concept of target cells in relation to plant hormones. The effect of removing exogenously supplied cytokinin at various times during a 24 h induction period is reported. There is no evidence that cytokinins act by a 'triggering' effect with a long half life, the response in the target cells being the same as that expected from the amount of cytokinin and cytokinin metabolite remaining in the tissue at the time of extraction. Either continuous presence of cytokinin is needed or any trigger action is short lived, and continuous 're-triggering' is needed to achieve maximum response.

Hyphal anastomosis inPyricularia oryzae cav.

Hyphal anastomosis inPyricularia oryzae occurs naturally in the lower epidermal cells and in the vascular bundles of young lesions on rice. In those cells the invading blast fungus are active. Two hyphal cells lying side by side start an anastomosis by forming two, one from each, very short penetration pegs which are opposite to each other. The cell wall of the pegs and the wall in the vicinity of them are then gradually eliminated and thus form a fusion aperture of 0.2–0.6 μm in diameter that is big enough for the migration or exchange of nucleus and cytoplasm between two hyphal cells. The explanation of genetical variation inP. oryzae may be sought on the basis of the ultrastructural evidence of hyphal anastomoses presented in this paper.

Histological changes associated with virus localization in TMV-infected Pinto bean leaves

Light and scanning electron microscopy of TMV-infected bean leaf tissue revealed severe damage of epidermal and palisade cells in the necrotic lesion. Sometimes, the adjoining mesophyll cells were affected but the lower mesophyll and lower epidermal cells did not show cytopathic changes leading to collapse and necrosis of cells in a local lesion. Fluorescent microscopy demonstrated accumulation of fluorescent metabolites extending 4 to 5 mm beyond the lesion perimeter and electron microscopy failed to detect virus in this outer margin of the lesion. Histochemical tests indicated that the appearance of fluorescent metabolites corresponded with extensive callose formation in the cells bordering the lesion. Inhibition of necrosis by either ascorbate infiltration or elevated temperature treatment resulted in the absence of fluorescent metabolites and also of callose deposition. However, mechanically injured, ascorbate infiltrated tissue showed callose deposition suggesting callose formation was not inhibited by ascorbate. The significance of these cellular changes in relation to virus localization is discussed.

Epidermal studies in some species ofAdiantum L.

Epidermal morphology of 22 species, including 2 varieties ofAdiantum is described. The upper and lower epidermal cells are either rectangular or irregular in shape and generally arranged parallel to the veins. The anticlinal walls of the intercostal cells are usually deeply sinuous. The costal cells are narrower, much elongated with sinuous walls except inA. cuneatum, A. fergusoni andA. formosum in which the cells are straight walled. Stomata are anomocytic type, the largest ones occur inA. macrophyllum, the smallest inA. peruvianum. Uniseriate, 2–4 celled, thick-walled acicular hairs occur in 5 species ofAdiantum. Characteristic “Spicular Cells” have been obsreved inA. macrophyllum.

The Role of the Epidermis in the Histopathogenesis of Lichen Planus

Detailed enzyme histochemical studies were performed on 18 biopsy specimens of lichen planus. The majority of the biopsies came from patients with acute lichen planus, but 3 were obtained from hypertrophic lesions of long standing. The most striking finding was a marked apparent depression of respiratory enzyme activity in the affected epidermis using techniques for the demonstration of succinic dehydrogenase, cytochrome oxidase and NAD diaphorase activity. Decreased epidermal cell turnover, damage to lower epidermal cells where these enzymes normally show maximal activity or local anoxia are amongst the factors which are considered to be responsible for this enzyme depression. No increase in various hydrolytic enzymes associated with lysosomal activity, such as nonspecific esterase and acid phosphatase, could be demonstrated in areas where basal cell necrosis was a marked feature. A great reduction in the number of melanocytes was indicated by the dopa-oxidase reation in active lesions. The relevance of these various findings with particular reference to the role of the lower epidermis in the histogenesis of lichen planus is discussed.

Iwanoff Effect in Leaves of Cotton (Gossypium hirsutum)

AbstractWhen a leaf is excised from a plant by cutting the petiole in air, the stomata sometimes exhibit an “Iwanoff effect” or temporary increase of aperture before entering the phase of hydroactive closure. Simultaneous and separate measurements of transpiration from upper and lower leaf surfaces, derived from thermocouple psychrometers, photosynthesis measurements from either or both surfaces obtained with an Infrared Gas Analyser and measurements with a nitrous oxide diffusion porometer have been made on leaves of Gossypium hirsutum (cotton) before and after severing the petiole. The effect of previous illumination of the plant on the occurrence of the Iwanoff effect has been studied. The results obtained are consistent with the suggestion that an Iwanoff effect is observed when there is little or no water stress, but fails to appear if water stress has developed, even though it may not yet have reached the level at which hydroactive stomatal closure would occur. Furthermore the Iwanoff effect appears to be limited to the stomata of the upper surface in cotton leaves. This seems to be due to the greater accessibility of the upper than the lower epidermal cells, to the water demand of the internal tissues which follows excision. Evidence is also presented to show that the adaxial stomates do not necessarily close completely in the dark.

Internal Leaf Surface and Stomatal Abundance in Arctic and Alpine Populations of Oxyria Digyna

Internal leaf surface is greater in alpine populations of Oxyria digyna than in arctic populations grown under identical conditions. Outlines of lower epidermal cells of leaves vary among 10 arctic and alpine populations. Numbers of stomata, as well as epidermal cells, per unit area in the upper epidermis increase from north to south. Such a trend is not found in the lower epidermis. An alpine population from Mt. Washington has many more stomata per unit area on the lower epidermis than the upper, suggesting a closer affinity to the European alpine populations and to arctic populations than to its western North American and alpine conditions may be due to the development of ecological races which differ in structure and metabolic potential

Chloroplastic Structures in the Epidermis of Spinach Leaves

1. Leaves of Spinacia oleracea have the typical structure of mesophytic, dicotyledonous leaves. 2. Pigmented granules, which are distinct morphological structures and resemble the grana of mesophyll chloroplasts, are present in the cytoplasm of both upper and lower epidermal cells of spinach leaves. 3. These granules are of two types: light-green, an average of 1.1 μ in diameter; and yellow-green, an average of 1.2 μ in diameter. Both types demonstrate fluorescence and birefringence; and, therefore, they may be chlorophyll-containing structures. They may possibly be either immature or degenerate chloroplasts. 4. Glycerine and formalin treatment of the epidermal tissues does not affect the birefringence of the granules even after 12 days, though after 30 days in glycerine their birefringence may be lost.

Lower epidermis of leaf midrib as an imdicator of its hardness in sugarcane

(a) Number of Silica cells per unit area in the lower epidermis of leaf midribs of thirteen varieties of sugarcane, covering a wide range of hardness of leaf midribs was noted. P.O.J. 2725,Sewari (Nargori group) and Co 299 had on the average, 39·4 to 41·4 of them in a circular field which was 470 µ in diameter, whereas in Co 331, Co 513 andChin (Saraitha group) the number was as low as 13·3 to 14·5 in the same area. (b) Silica cells were found to have no consistent association either with the weight required to puncture the midrib on its convex side or with the thickness of the outer cell wails, both the correlation coefficients being too tow to be significant even at 10%, level. (a) The range of the thickness of outer walls of long cells in the epidermis as expressed in the divisions of the eye-piece micrometer was from 14·5 inSewari (Nargori group) to 23·5 in Co 421 (I division = 0·22µ). (b) The varietal differences were significant at 5% level. (a) Weights required to puncture a midrib varied from 598 gm. inChin to 1273 gm. in Co 285 and these for the varieties studied were found to be significantly different at 5% level. (b) The correlation coefficient between this character and the thickness of cell walls was found to be + 0·6377 which was significant at the same level. (c) The thickness of outer wall of long cells of lower epidermis could, therefore, be used as a fairly reliable indicator of the puncture-weight and, therefore, of the hardness of a leaf midrib. 4. The erratic behaviour of four varieties, namely Co 285, P.O.J. 2725,Chin andSaraitha (Saraitha group) in which the puncture-weights were found to be bisher or lower than those warranted by the thickness of cell walls was explained by the size and number of vascular bundles and the sclerenchymatous cuchions together with the thickness of sclerenchymatous cell walls when these characters were considered in relation to the size of a midrib in cross-section. All the four varieties were found to be abnormal for one character or the other.