Studies on the control of mitotic activity

Summary A tetraploid cell population was produced in the primary root meristem of Pisum sativum by one-half hour treatments with various concentrations of colchicine. The tetraploid population so produced was found to be reasonably synchronous in its passage through successive mitotic cycles with the degree of synchrony being more or less proportional to the concentration of colchicine used. The average time between mitoses appears to be of the order of 12 hours which agrees well with previous estimates. Treatments of roots containing tetraploid populations with 2.52 × 10^–5 M. actidione for 15 minutes were used to demonstrate the possibility of using the system for studies on the differential susceptibility of cells at different stages of the mitotic cycle.This work was carried out under contract number RG-4835 of the National Institutes of Health, United States Public Health Service, and an Institutional Grant from the American Cancer Society.Contribution number 59-26 of the Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan.Predoctoral Fellow (CF-9871) of the National Cancer Institute, United States Public Health Service     

DEVELOPMENT AND GERMINATION OF THE AZOTOBACTER CYST

The fine structure of Azotobacter vinelandii has been studied by means of electron microscopy of ultrathin sections made of the encysting and germinating cells. The organisms were fixed with KMnO₄ and embedded in epoxy resin. On an encystment medium the rod-shaped bacteria begin to assume an almost spherical form and then bark-like exine appears in 1½ to 2 days. The exine thickens and an electron permeable intine forms between it and the shrinking cell body. In 5 days the intine makes up more than half of the cyst volume and begins to show a definite two-layered structure. Meanwhile the peripheral bodies, which may be extensions of the cell membrane of the vegetative cell, disappear as the encystment progresses. The cell wall and membrane of the vegetative cell remain demonstrable as the confining structure of the shrinking central body of the mature cyst. In this central body lipoidal globules appear together with aggregations of nuclear material. Cyst germination begins with an increase in the size of the central body at the expense of the intine. The nuclear aggregations become more diffuse and the lipoidal globules disappear. The exine may be pushed outward and the bark-like fragments separate as the emerging vegetative cell develops. Invagination of the cell wall and membrane may occur at this stage leading to cell division. Empty exines remain as horseshoe-shaped structures.     

A PLUCHEA HYBRID FROM THE PACIFIC

Two species of Pluchea have been introduced into the Hawaiian Islands in the present century. These are P. indica, native to southeastern Asia, and P. odorata, native to the western hemisphere. Both are erect shrubs. Within the past 30 years a third Pluchea taxon, a sprawling shrub morphologically distinct from the two species, has appeared in the Hawaiian Islands and on other islands in the tropical Pacific. On the basis of morphology, fertility, meiotic behavior, and other evidence, it is concluded that the third taxon is a hybrid between the two species. The hybrid is highly sterile; it has a limited capacity for asexual reproduction. Metaphase I configurations for both species were found to be 10_II; the most frequent configuration in the hybrid was 8_II + 4_I. The hybrid is given a binomial.     

Pathogenesis of hemosiderosis in lemurs: Role of dietary iron,tannin, and ascorbic acid

Clinical disease associated with excess iron deposition (hemosiderosis) in the duodenum, liver, and spleen occurs in captive lemurs. In this report we review the occurrence of hemosiderosis and related disease in the Zoological Society of San Diego lemur collection; we then define and describe potential pathogenic factors with the goal of establishing rational husbandry methods to limit or prevent the disease. At the San Diego Zoo, all 49 lemurs necropsied since 1968 were hemosiderotic, the severity increasing with increasing age; liver and kidney disease were common. Our review of iron metabolism, current knowledge on the pathogenesis of hemosiderosis in humans, and the diets of captive and wild lemurs reveals several key dietary substances that may contribute to lemur hemosiderosis: iron, tannins, and ascorbic acid. In captivity, excess dietary iron (commercial monkey chow) and high levels of ascorbic acid (citrus fruits) lead to enhanced iron uptake and increased toxicity of stored iron due to free radical formation. In the wild, lemurs have an unusual preference for leaves, fruits, and bark high in tannin, a polyphenolic secondary plant compound that rapidly chelates iron, protein, and minerals in the gastrointestinal (GI) tract, preventing their absorption. These findings suggest that hemosiderosis in captive lemurs results from a diet high in iron, high in ascorbic acid, and lacking in tannin. Immediate correction of captive diets may limit hemosiderosis in lemurs in the future.     

Tolerance of tannin by the shiitake mushroom,Lentinus edodes

Summary Tannin at 1% (w/v) did not inhibit the growth ofLentinus edodes, but did inhibitPleuroius florida, P. sajor-caju, P. cystidosus, Agaricus bisporus andVolvariella volvacea. The inhibition was not due to its acidity.

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Tolérance de Lentinus edodes aux ajouts de tannin

Résumé Le tannin à la concentration de 1% (p/v) n'inhibe pas la croissance deLentinus edodes, mais inhibe celle dePleurotus florida, P. sajor-caju, P. cystidosus, Agaricus bisporus, etVolvariella volvacea. L'inhibition n'est pas due à son acidité.

     

Characterization of the D-allose-mediated regulation of sugar transport in Chinese hamster fibroblasts

Exposure to D-allose has been demonstrated to lead to decreased 2-deoxy-D-glucose (2-DG) and 3-0-methyl-D-glucose transport in the V79 Chinese hamster lung fibroblast cell line. The effect of D-allose 1) was maximal after 4 hours exposure to the cells; 2) was optimal between 2.77 and 5.55 mM D-allose; and 3) led to a decreased Vmax for 2-DG transport with no change in the transport Km value. The decrease in 2-DG transport induced by D-allose was reversible and the reversal was differentially affected by cycloheximide, being blocked by a low concentration of cycloheximide (0.05 micrograms/ml) but not a high concentration of the inhibitor (5 micrograms/ml). D-allose did not competitively inhibit the transport of 2-DG while D-glucose under similar conditions yielded a Kl for 2-DG transport inhibition of 1.7 mM. Additionally, D-allose did not affect the phosphorylation of 2-DG by hexokinase in cell-free cytosol. The data indicate that D-allose has significant lowering effects on sugar transport activity. Additionally, while the sugar itself may be the active component in sugar transport regulation, the effect is not blocked by inhibition of protein synthesis but the synthesis of a regulatory protein(s) may be involved in the return of sugar transport following D-allose removal.     

Hormonal changes associated with fruit set and development in mandarins differing in their parthenocarpic ability

Satsuma [Citrus unshiu (Mak) Marc.] and Clementine [Citrus reticulata (Hort.) Ex. Tanaka, cv. Oroval] are two related species of seedless mandarins which differ in their tendency to set parthenocarpic fruits. Satsuma fruits naturally set parthenocarpically whereas Clementine mandarins show very low ability to set fruit in the absence of cross-pollination. The endogenous levels of gibberellins (GAs) and free and conjugated indole-acetic acid (IAA) and abscisic acid (ABA) throughout early stages of fruit development were investigated in seedless cultivars of both species. Analyses performed by full-scan combined gas chromatography-mass spectrometry (GC-MS) of extracts from ovaries at anthesis demonstrated the presence of GA₁₉, GA₂₀, GA₂₉, GA₁, GA₈, GA₃ and iso-GA₃ in Satsuma mandarin, whereas only GA₂₉, GA₃ and trace levels of GA₈ were detected in Clementine. At this developmental stage GA-like substances, as estimated by bioassay, reached their highest levels in Satsuma, while Clementine mandarins contained relatively lower levels. In both species the highest levels of free IAA were found at petal-fall stage at which time free ABA levels also peaked. Developing fruits of Clementine had higher amounts of both free IAA and ABA. In Satsuma, levels of conjugated IAA remained low throughout reproductive development whereas in Clementine they increased as the free form declined. In contrast, conjugated ABA was at low levels in Clementine but reached higher concentrations in Satsuma. These results suggest that in these mandarins the potential for setting parthenocarpic fruits is mainly influenced by the hormonal status of the fruit during the later stages of cell division and early stages of cell enlargement. Thus, the condition of low ability to set parthenocarpic fruits appears to be associated with lower levels of active GAs, lower capability to catabolize ABA to conjugated ABA and higher ability to conjugate IAA during this period.