Spatio‐temporal variation of salt marsh seedling establishment in relation to the abiotic and biotic environment

Contrary to our expectations, soil salinity and moisture explained little of the spatial variation in plant establishment in the upper intertidal marsh of three southern California wetlands, but did explain the timing of germination. Seedlings of 27 species were identified in 1996 and 1997. The seedlings were abundant (maximum densities of 2143/m² in 1996 and 1819/m² in 1997) and predominantly annual species. CCAs quantified the spatial variation in seedling density that could be explained by three groups of predictor variables: (1) perennial plant cover, elevation and soil texture (16% of variation), (2) wetland identity (14% of variation) and (3) surface soil salinity and moisture (2% of variation). Increasing the spatial scale of analysis changed the variables that best predicted patterns of species densities. Timing of germination depended on surface soil salinity and, to a lesser extent, soil moisture. Germination occurred after salinity had dropped below a threshold or, in some cases, after moisture had increased above a critical level. Between 32% and 92% of the seedlings were exotic and most of these occurred at lower soil salinity than native species. However, Parapholis incurva and Mesembryanthemum nodiflorum were found in the same environments as the native species. In 1997, the year of a strong El Niño/Southern Oscillation event with high rainfall and sea levels, the elevation distribution of species narrowed and densities of P. incurva and other exotic species decreased but densities of native and rare species did not change. The ‘regeneration niche’ of wetland plant communities includes the effects of multiple abiotic and biotic factors on both the spatial and temporal variations in plant establishment.     

Anti-tubulin immunofluorescence studies of recovery from vinblastine cytotoxicity in Chinese hamster cells

Antitubulin immunofluorescent staining was used to examine the relationship among crystal formation, mitotic arrest, and recovery potential in vinblastine-treated Chinese hamster cells. Although vinblastine caused a mitotic block at concentrations as low as 5 x 10(-9) M, it induced tubulin crystal formation only at concentrations higher than 10(-6) M. At these higher concentrations, cells took 48-72 h to recover after return to normal medium. This extended period of time was apparently needed for breakdown of the crystals and regeneration of normal cytoplasmic microtubules. At concentrations less than 10(-6) M, although the mitotic block was still effective, no crystals were present. Possibly because of this lack of crystal formation, the cells recovered rapidly, generating cytoplasmic microtubules within 30 min, and beginning to undergo mitosis within 60 min. These findings tend to support biochemical evidence that tubulin binds to vinblastine at two types of binding site: a high affinity, low capacity site, responsible for tubulin disaggregation; and a low affinity site, responsible for protofilament splaying.     

Effects of gamma-irradiation on chromosomes of cultured lymphocytes from rheumatoid arthritis patients and their family members

Increased rates of spontaneous or induced chromosome breakage are seen in many types of diseases, including the 'collagen-type' autoimmune diseases. Using a 60Co gamma cell, we irradiated lymphocyte cultures from three related rheumatoid arthritis patients, their immediate family members, and two unrelated rheumatoid arthritis patients. Although these individuals had not shown abnormally high levels of spontaneous chromosome breakage, they did show an abnormal sensitivity to irradiation, which was manifested in several ways. Two of the probands showed induced breakage rates that were twice as high as those seen in controls. In addition, the reduction of mitotic index, due either to increased cell death or to induction of a G2 lag period, was higher in the arthritis group (including non-symptomatic family members) than in the control group. Finally, we observed a high frequency of an unusual type of cell in the arthritis group. These unusual cells resembled c-anaphases seen with extended colcemid treatment, and may indicate that the mitotic apparatus in cells from this group is particularly sensitive to ionizing radiation.     

Effects of testosterone on messenger ribonucleic acid and protein synthesis in rat seminal vesicle

In a previous report [Higgins et al. (1976) Biochem. J. 158, 271–282] we described the effects of alterations in androgen status on the synthesis of two basic secretory proteins of the rat seminal vesicle. In the present paper we examine the effects of testosterone on the activity of mRNA in the seminal vesicle. Total cellular poly(A)-rich RNA was isolated and translated in a cell-free system prepared from wheat germ. Translation products were separated on denaturing polyacrylamide gels and the protein bands corresponding to the two basic secretory proteins were identified immunologically. Incorporation of radioactive methionine into these bands was taken as a measure of the individual mRNA activities. Total mRNA activity was estimated by radioactivity in total acid-precipitable material. The results show that 1 to 2 weeks after castration the activities of mRNA molecules for the basic secretory proteins were decreased 10–20-fold on a tissue basis. Testosterone given in vivo rapidly and substantially restores mRNA activity to normal. Since these changes correlate closely with variations in the rates of synthesis of the secretory proteins in whole cells it suggests that androgenic steroids control protein synthesis chiefly via mRNA availability. In this respect their action resembles those of other steroid hormones acting in other systems. However, these effects of testosterone on the mRNA molecules for the major secretory proteins could not be distinguished from those on total mRNA. Thus the proportion of the total mRNA population accounted for by the two specific mRNA molecules showed less than a 2-fold variation with androgen status. Similarly the two secretory proteins always accounted for 25–33% of general protein synthesis. This is in sharp contrast with the markedly differential effects of other steroid hormones controlling synthesis of major proteins in other well-studied systems. We interpret our results as indicating that testosterone regulates the mRNA population of the seminal vesicle as a whole.     

Heparin enhances fibrinolysis in B16 mouse melanoma cells

The fibrinolytic activity of two tumorigenic B16 mouse melanoma lines was stimulated by exogenous hog mucosal or beef lung heparin. In contrast, the activity of two normal fibroblast lines was unaffected. The degradation of ¹²⁵l-fibrin was increased up to 3.6-fold by the addition of heparin. Chondroitin-4-sulfate or dextran sulfate did not change the fibrinolytic activity of three of the cell lines, but, at concentrations where enhancement by heparin was much reduced, the activity of one of the B16 melanoma lines was somewhat elevated. Antithrombin III did not alter the plasminogen activator activity of the B16 cell lines, but, in the presence of exogenous heparin, the enhancement of fibrinolysis was greatly reduced. The polymers were not cytotoxic during the assay period, and, had little affect on the plating efficiencies of the lines.