Detection of a non-structural protein of M r 11 000 encoded by the virion DNA of maize streak virus

A polypeptide of approximately 11 000 daltons (11 kDa protein) encoded by an open reading frame (10.9 ORF) from the virion sense of maize streak virus (MSV) DNA has been detected among the products of in vitro translation reactions programmed with RNA from infected maize plants and also in total protein extracts from infected leaves. The 11 kDa protein has not been detected in virions and is therefore proposed to have a nonstructural role.Viral DNA with an additional in-frame translation stop codon in the 10.9 ORF was not infectious when transmitted to maize plants via Agrobacterium tumefaciens agroinfection, suggesting that the 10.9 ORF may be essential for virus function. Computer comparison data show that equivalent ORFs in wheat dwarf virus (WDV) and digitaria streak virus (DSV) have some sequences in common with the 10.9 ORF of MSV. Further-more, the absence of similar sequences in geminiviruses which infect dicotyledonous plants suggests that the 11 kDa protein and its putative homologs in WDV and DSV have a function necessary only for those geminiviruses which infect the Gramineae.The significance of the 11 kDa protein in relation to expression of the virion sense DNA of MSV is discussed.     

Inverse relationships between steroid concentration and volume in preovulatory follicles of the golden hamster

In order to investigate variations in the microenvironment of oocytes within a cohort of maturing follicles the follicular volumes as well as the intrafollicular concentrations of oestradiol (E2) and progesterone (P) were measured in the golden hamster. At 10 h before ovulation the follicular volumes varied from 0.009 to 0.037 mm3 (mean +/- SD: 0.0187 +/- 0.0071 mm3; n = 36). Large follicles (greater than 0.025 mm3; n = 8) contained statistically significantly lower E2 and P levels (30.1 +/- 10.4 and 517 +/- 113 mumol/l, respectively) than the medium sized group (less than 0.025 and greater than 0.015 mm3; n =20): 46.9 +/- 16.0 (P less than 0.02) and 919 +/- 264 (P less than 0.0001) mumol/l, respectively. Small follicles (less than 0.015 mm3) showed the highest steroid levels: 97.0 +/- 33.3 and 1590 +/- 517 mumol/l for E2 and P (P less than 0.001 versus the medium sized group values). Correlation coefficients for the steroid concentrations and the follicular volumes appeared to be -0.674 for E2 and -0.612 for P (P less than 0.001). At the time studied a positive correlation between E2 and P concentrations in the follicles was found: r = 0.655 (P less than 0.001). The mean ratios of intrafollicular over serum steroid concentrations appeared to be approx 36 x 10(3) in the case of E2 and about 17 x 10(3) in the case of P. These results clearly show that there is an inverse relationship between follicular volume and intrafollicular steroid concentrations. The presence of a fine regulatory mechanism for a collective maturation of follicles is hypothesized.     

Gaps in the canopy: the missing dimension in vegetation dynamics

Canopy gaps are important as entry points for new genotypes and new species into many types of vegetation, yet little is known about them in any type of vegetation but forests. Forest gaps are too large for manipulative experiments to be readily undertaken, and hitherto grassland gaps have been too small to be easily mapped. Preliminary results from mapping small (>1 cm) grassland gaps with a new fibre-optic device suggest that experiments need to be performed at a smaller physical scale than has hitherto been achieved.     

Seasonal carbon isotope discrimination in a grassland community

Summary Grassland communities of arid western North America are often characterized by a seasonal increase in ambient temperature and evaporative demand and a corresponding decline in soil moisture availability. As the environment changes, particular species could respond differently, which should be reflected in a number of physiological processes. Carbon isotope discrimination varies during photosynthetic activity as a function of both stomatal aperture and the biochemistry of the fixation process, and provides an integrated measure of plant response to seasonal changes in the environment. We measured the seasonal course of carbon isotope discrimination in 42 grassland species to evaluate changes in gas exchange processes in response to these varying environmental factors. The seasonal courses were then used to identify community-wide patterns associated with life form, with phenology and with differences between grasses and forbs. Significant differences were detected in the following comparisons: (1) Carbon isotope discrimination decreased throughout the growing season; (2) perennial species discriminated less than annual species; (3) grasses discriminated less than forbs; and (4) early flowering species discriminated more than the later flowering ones. These comparisons suggested that (1) species active only during the initial, less stressful months of the growing season used water less efficiently, and (2) that physiological responses increasing the ratio of carbon fixed to water lost were common in these grassland species, and were correlated with the increase in evaporative demand and the decrease in soil moisture.     

Glucocorticoid effects on zinc transport into colostrum and milk of lactating cows

Colostrum Zn concentrations were measured in eight randomly selected Holstein dairy cows. Overall mean Zn concentrations were highest within 12 h postpartum (257 +/- 14 microM, mean +/- SEM), fell to 141 +/- 8 microM by 24 h, and then declined at a linear rate of 30 microM/d during the following 48 h. Zn concentrations at 3 d (82 +/- 5 microM) were not different from 150-d milk samples (72 +/- microM). In a second experiment, 32 early-gestation cows were blocked by stage of lactation into four groups in a randomized block design and injected with 0, 15, 30, or 45 mg of dexamethasone. Milk and blood samples were collected at 0, 12, and 24 h after injection and analyzed for Zn, and for fat, protein, and lactose in milk. Cows administered 0 and 15 mg of dexamethasone showed no difference in milk Zn concentrations compared to pretreatment measurements; however, milk Zn concentrations in cows administered 30- and 45-mg doses increased significantly. Plasma cortisol decreased in the dexamethasone-treated cows. Plasma Zn and milk fat, protein, and lactose did not change. These data indicate that glucocorticoids can mediate Zn uptake and transport by the mammary glands of lactating cows and suggest that the high Zn concentration in colostrum could be a result of the preparturient surge of cortisol.     

Binding protein dependent transport of C4-dicarboxylates in Rhodobacter capsulatus

The characteristics of malate transport into aerobically grown cells of the purple photosynthetic bacterium Rhodobacter capsulatus were determined. A single transport system was distinguished kinetically which displayed a K_t value of 2.9 ± 1.2 μM and V_max of 43 ± 6 nmol · min^-1 · mg^-1 protein. Competition experiments indicated that the metabolically related C4-dicarboxylates succinate and fumarate are also transported by this system. Malate uptake was sensitive to osmotic shock and evidence from the binding of radiolabelled malate and succinate to periplasmic protein fractions indicated that transport is mediated by a dicarboxylate binding protein. The activity of the transport system was studied as a function of external and internal pH and it was found that a marked activation of uptake occurred at intracellular pH values greater than 7. The use of a high affinity binding protein dependent system to transport a major carbon and energy source suggests that Rhodobacter capsulatus would be capable of obtaining growth sustaining quantities of C4-dicarboxylates even if these were present at very low concentrations in the environment.     

island biogeography of Day Geckos (Phelsuma) in the Indian Ocean

Summary Step-wise multiple regression was employed to probe the determinants of species diversity of day geckos (Phelsuma) in the Indian Ocean. Independent variables were area, elevation, and two measures of isolation. Distance from Madagascar and island height (an indicator of habitat diversity) were the two most important predictors of species richness. Similar studies on other taxa rarely find isolation to be a major factor. The relatively poor dispersal abilities of reptiles may explain why isolation, rather than attributes of the islands, are more important in this case. The regressions also indicate that habitat diversity (assumed to correlate with maximum island elevation) is more important than area per se in determining species diversity. These results agree with predictions of the equilibrium theory of island biogeography, but historical processes have also greatly influenced species richness.     

Spatial variation in larval concentrations as a cause of spatial variation in settlement for the barnacle,Balanus glandula

Summary Settlement rates of the high intertidal barnacle, Balanus glandula, were monitored at three sites in the rocky intertidal zone in Central California simultaneously with measurements of larval concentrations in the adjacent water column. In both 1983 and 1984, settlement rates onto vacant substrate differed among the sites by nearly two orders of magnitude. For all sampling dates, this spatial variation in settlement mirrored the spatial distribution of Balanus glandula cyprid concentration in the water column. A perfect rank correlation was found between cyprid concentrations near a site and subsequent settlement. A noteworthy observation was that the sites switched rank in their settlement rates from 1983 to 1984. This change in settlement rankings matched a switch in rankings for cyprid concentrations.Settlement itself appears to be an important cause of the spatial pattern of cyprid concentrations. Comparing the rates of settlement to estimates of the number of cyprids available at a site suggests that settlement causes a large drain on the cyprid population as a water mass passes over successive sites. No consistent spatial patterns were found in the distribution of other major plankton groups (calanoid copepods) that are similar in size to Balanus cyprids but do not settle.The large differences in settlement rates among these sites were previously shown to be a leading cause of large differences in the structure of benthic barnacle populations. The close correspondence shown here between these large differences in settlement and differences in larval concentrations suggests that nearshore oceanic processes affecting larval arrival contribute to the control of benthic community structure.