Albino Tissues Research Articles

Import and unloading of 14C assimilate into nonphotosynthetic portions of variegated Coleus blumei leaves

Variegated leaves of Coleus blumei Benth. were exposed for 4 h to 1.85 MBq 14CO2 to study the movement of 14C assimilate from green to albino portions of the lamina. Autoradiographs showed considerable 14C activity in both veins and mesophyll of the central albino regions, whether the lamina was left intact or various parts of it were severed or removed prior to 14CO2 exposure. However, when all of the photosynthetic tissue was removed, virtually no label appeared in the albino tissue. Autoradiographs of chromatographed extracts of albino regions from intact leaves showed that sucrose was the most abundant labeled compound and that imported assimilate was unloaded and metabolized into a number of other compounds. The albino region is therefore a genuine sink. No label was imported into any part of mature leaves when lower leaves were fed 14CO2, and young developing leaves ceased to import in the tip-to-base progression typical of dicotyledonous leaves.

Ocular distribution of topically applied adrenaline in albino and pigmented rabbits.

Systemic absorption, ocular distribution and ocular metabolism in albino and pigmented rabbit of topically applied 1% [3H]l-adrenaline eye drops was studied by liquid scintillation counting and thin layer chromatography. The effect of adrenaline on the pupillary diameter was also registered. The peak plasma level of adrenaline was reached at 150 min. The corneal adrenaline metabolism was substantial, but did not vary with the rabbit strain. At 30 min after instillation, the total adrenaline concentration of pigmented iris and ciliary body exceeded that of corresponding albino tissues. At 180 min the drug concentration of the iris and ciliary body did not differ between the rabbit strains. The time course of adrenaline induced mydriasis was equal in both rabbit strains. Since neither total adrenaline concentration at 180 min nor the time course of adrenaline induced mydriasis differed between the rabbit strains, the higher initial adrenaline uptake by pigmented tissues is not explained by pigment binding. It is proposed that the increased initial binding of adrenaline by pigmented tissues is caused by a difference between pigmented and albino tissues in the number of adrenergic neurones; this is also supported by the literature.

Effect of ocular pigmentation on pilocarpine pharmacology in the rabbit eye. I. Drag distribution and metabolism

Systemic absorption, ocular metabolism and ocular distribution of pilocarpine were studied after ocular application of 2% solution of [ 3H]pilocarpine in albino and pigmented rabbits. Systemic absorption of ocularly applied pilocarpine was rapid. In the eye pilocarpine was efficiently and equally metabolized to pilocarpic acid in albino and pigmented rabbits. Pilocarpine accumulated in the pigmented iris, ciliary body, and choroid and retina more than in the corresponding albino tissues. Pretreatmeni with non-labelled pilocarpine did not affect the concentration of [ 3H]piIocarpine in the pigmented iris, ciliary body or choroid and retina, indicating a high capacity for drug bunding in these tissues.

A RECONSTRUCTION OF CELL DEVELOPMENT IN THE SHOOT APEX OF MAIZE

Somatic mutations were induced in maize embryos in order to follow the albino‐tissue patterns in mature plants. A reconstruction of cellular development in the shoot apex has been attempted. Two strains of maize were employed, wd/Yg2 and pastel‐8549/y1 for seed irradiation with gamma rays. After mature plants had developed from this radiated seed, the sectored plants were analyzed in detail for their patterns of albino tissue. The location and frequency of these patterns were correlated with cell number at various sites of the initial shoot apex in order to deduce the number of cells contributing to each frequency class. Various lines of evidence lead to the conclusion that the cellular differentiation in the shoot apex is organized and a relatively stable process. Apparently a few cells in the apical dome provided daughter tissue for the upper half of the maize plant. Various sector patterns are diagrammed and the position of their albino tissue is explained in relation to the location of a specific cell in the apex.

PLASTID FUNCTION IN PLANT TISSUE CULTURES. I. PORPHYRIN SYNTHESIS BY DARK‐GROWN HAPLOID AND DIPLOID ALBINO CULTURES

Tissue cultures lacking chlorophyll formed porphyrins when fed δ‐aminolevulinic acid, a precursor of tetrapyrroles. When grown in the dark tissues from Ginkgo biloba L., Taxus, and Rosa formed protoporphyrin and several unidentified compounds. When grown in the light cultures did not form these pigments. The protoporphyrin was detected in the tissues after 3–6 hours incubation with δ‐aminolevulinic acid; it was localized in the plastids by ultraviolet light microscopy and was identified by extraction procedures, chromatography, and absorption spectroscopy. No magnesium protoporphyrins were found, suggesting that chlorophyll synthesis was blocked at this point. Both male and female haploid albino tissues from Ginkgo formed protoporphyrin. The female albino tissue was derived from a chlorophyll‐containing tissue culture from the female gametophyte by serially subculturing the green tissue in the dark. Upon exposing the female albino tissue to light, no greening occurred. The treatments used thus far have not caused chloroplasts to develop in the haploid albino tissues, even though the tissues contain many amyloplasts. Concurrent with the loss of chloroplasts, the female tissue loses all capacity to differentiate specialized cells, such as tracheids, resin cells, and chlorenchyma.

Plastid Function in Plant Tissue Cultures. I. Porphyrin Synthesis by Dark-Grown Haploid and Diploid Albino Cultures

Tissue cultures lacking chlorophyll formed porphyrins when fed δ-aminolevulinic acid, a precursor of tetrapyrroles. When grown in the dark tissues from Ginkgo biloba L., Taxus, and Rosa formed protoporphyrin and several unidentified compounds. When grown in the light cultures did not form these pigments. The protoporphyrin was detected in the tissues after 3–6 hours incubation with δ-aminolevulinic acid; it was localized in the plastids by ultraviolet light microscopy and was identified by extraction procedures, chromatography, and absorption spectroscopy. No magnesium protoporphyrins were found, suggesting that chlorophyll synthesis was blocked at this point. Both male and female haploid albino tissues from Ginkgo formed protoporphyrin. The female albino tissue was derived from a chlorophyll-containing tissue culture from the female gametophyte by serially subculturing the green tissue in the dark. Upon exposing the female albino tissue to light, no greening occurred. The treatments used thus far have not caused chloroplasts to develop in the haploid albino tissues, even though the tissues contain many amyloplasts. Concurrent with the loss of chloroplasts, the female tissue loses all capacity to differentiate specialized cells, such as tracheids, resin cells, and chlorenchyma.

Tyrosinase Activity in Melanocytes of Human Albinos

Albinism is a condition that has attracted medical interest and description for many centuries. Until the past decade, however, efforts were largely confined to the publication of extensive pedigrees demonstrating the autosomal recessive inheritance of the trait and other reports illustrating the frequency of co-existing congenital anomalies-presumably also recessive. Histologic and histochemical studies were few and generally inadequate; these were based largely upon the work of Bruno Bloch who in 1917 demonstrated the formation of a pigment resembling melanin in normal epidermal melanocytes following incubation of skin sections in a solution of 1-dihydroxy-phenylalanine (1). The “dopa reaction” was an important discovery, not only in the study of the biosynthesis of melanin, but also as a useful histochemical method for the identification of melanocytes in tissues with a normal capacity for pigment formation. Albino tissues were shown, soon thereafter, not to possess dopa activity (2), and the erroneous assumption was subsequently made that melanocytes, as well as the melanogenic enzyme “dopa oxidase” which they contained, must be absent in this condition (3). In 1952, however, Becker, Jr. et al. (4) first announced that they had demonstrated “amelanotic” melanocytes in human albino skin using gold impregnation, and they concluded that the population density of such cells was the same as that found in normally pigmented skin. Their results have generally been accepted, although there is a considerable body of recent evidence indicating that the gold impregnated cells in question may not be melanocytes at all (5, 6). Other investigations have, however, now established the presence of melanocytes in albino tissues beyond any reasonable doubt. These cells have been identified in electron micrographs of hair follicles (7) and also of neoplasms, i.e., nevi and melanomas (8, 9).

Comparative Physiology of Green and Albino Corn Seedlings.

Previous comparative studies of green, albino, and variegated plants have shown higher levels of soluble nitrogenous compounds and lower levels of protein nitrogen in albino or in variegated than in green tissues (6, 14). The soluble nitrogen level was reduced and the protein level was increased when carbohydrates were supplied to albino tissues and plants. Groner (6), on the basis of such findings, postulated that when the supply of carbohydrate from the endosperm of an albino corn seedling became limiting, the seedling would hydroiyze its proteins, utilizing some of the products of hydrolysis in metabolism. The soluble nitrogenous substances, notably some amino acids, that could not be metabolized were thought to accumulate.