Rhinanthus: a tool for restoring diverse grassland?

The restoration of species-rich grasslands is often hindered by high residual soil fertility as a result of, e.g., intensive farming. The establishment of a diverse range of target species on such sites requires the reduction of soil fertility or of the vigour of competitive plants. Current methods to achieve these aims are often unsuccessful or complicated and expensive. It has been suggested thatRhinanthus species could be used to decrease the growth of competitive plants and enhance species diversity. We review evidence for this potential and suggest five key attributes that makeRhinanthus species a practical restoration tool.Rhinanthus species are natural components of species-rich grasslands (attribute 1), and seed of some species is relatively low cost and easily obtainable (2). Recent work has shown that certainRhinanthus species reduce the vigour of competitive species, especially agricultural grasses, and allow establishment and persistence of target species (3). We analyze demographic data and show that certainRhinanthus species have the ability for rapid population growth and spread, even in fertile grasslands (4). We also show that it is relatively easy for land managers to limit the population size ofRhinanthus species and prevent damage (e.g. excessive loss in production or invasion by weeds) to grasslands by excessive densities (5). We give suggestions for further research, including: the range of species-poor grasslands into whichRhinanthus can be introduced successfully and whichRhinanthus species should be used; the mechanisms by whichRhinanthus enhances diversity in restored grasslands; whether the ecotype or subspecies ofRhinanthus used affects restoration success; how management methods affect population growth and spread ofRhinanthus; and whether other parasitic plants could be used in habitat restoration.     

Impairment of lymphocyte mobilization from lymphoid organs by granulomatous infection.

The kinetics of the lymphocytosis induced by intravenous (iv) injection of the lymphocyte mobilizing agent polymethacrylic acid (PMAA) were studied in C3H mice chronically infected with Mycobacterium lepraemurium and in normal controls. After the tenth week of infection, lymphocyte mobilization to peripheral blood by PMAA diminished progressively and at 18 weeks it was significantly less than normal (P < 0.05). ⁵¹Chromium-labeled lymph node cells from syngeneic donors were given iv to 18-week infected or control mice and allowed to home for 18 hr prior to PMAA injection. Radioactivity in the blood of infected mice was significantly less than levels in controls at 2, 4, and 6 hr after PMAA (P = 0.02). Similar studies of splenectomized mice from the normal and infected groups indicated that impairment of lymphocyte mobilization in infected mice was secondary to lymphocyte trapping by the spleen and lymph nodes.     

Quality of plasma cholesterol measurements in primary care.

Three surveys were made of the quality of plasma cholesterol measurements performed with a commercial desktop analyser (BCL Reflotron) in primary care. Each survey included three specimens, and results were received from 37, 61, and 69 participants. Although many participants obtained satisfactory results, 8.6% of the results differed by 1.0 mmol/l or more from the target values, and the overall between instrument dispersion of results was 1.3 times that between hospital laboratories. It was found that common sources of error were poor technique and the use of outdated reagent strips. Users of such instruments outside the laboratory need help and advice with training, and guidelines for this are provided. The main recommendations are that users should establish contact with a local clinical chemistry laboratory for training and support and should participate in external quality assessment schemes.     

Possible Involvement of Altered Gibberellin Metabolism in the Induction of Tomato Irregular Ripening in Dwarf Cherry Tomato by Silverleaf Whitefly

External and internal tomato irregular ripening (TIR) symptoms were associated with the feeding of silverleaf whitefly (SLW), Bemisia argentifolii Bellows and Perring. Four experiments consisting of various soil drench applications of GA₃ (100 ppm) and cycocel (CCC, an inhibitor of GA biosynthesis; 1,000 and 2,000 ppm) were applied to dwarf cherry tomato cv. Florida Petite in the presence and absence of SLW in an attempt to mimic the disorders induced by the SLW. The application of GA₃ induced external and internal TIR symptoms similar to the SLW-induced disorder. Minimal TIR-like symptoms also occurred in the control and CCC treatments. Internal TIR symptoms in GA₃, GA₃ plus SLW, and GA₃ plus CCC treatments ranged from 66% to 97% throughout the experiments. The incidence of external TIR symptoms was highest in the GA₃ plus SLW treatment compared with the other treatments. CCC reduced the incidence of external TIR symptoms induced by GA₃ or GA₃ plus SLW treatments. However, CCC-treated plants also attracted more oviposition and higher populations of SLW and consequently induced a greater incidence of TIR symptoms than SLW treatment alone. Furthermore, although low SLW populations may be associated with low external TIR symptoms, internal TIR symptoms almost always remained high in infested plants. The results suggest that the TIR disorder in dwarf cherry tomato which is induced by the SLW may be a gibberellin-regulated disorder. Received May 27, 1997; accepted September 26, 1997     

Endopolyploidy in Diploid and Tetraploid Maize (Zea mays L.)

Nuclei from different tissues such as stem, mesocotyl, nodalroot and root tip of diploid and tetraploid maize were isolated,stained with propidium iodide and passed through an EPICS-751flow-cytometer cell sorter. Variations in flow histograms wereobserved in different tissues. Stem tissues of both the diploidand tetraploid had two peaks representing G1 and G2 somaticnuclei. The remaining tissues in both the diploids and tetraploidsexhibited three peaks. The first peak observed in these tissuesrepresents G1 somatic nuclei of the lowest ploidy level. Thesecond peak represent G2 somatic nuclei of the lowest ploidylevel+G1 somatic nuclei of the next ploidy level. The thirdpeak represents G2 of the higher ploidy level+G1 somatic nucleiof the next higher ploidy level. Statistically significant differenceswere observed between the diploid and tetraploid maize tissueswith respect to nuclei distribution in the higher ploidy levelpeaks implying variation in the degree of endopolyploidy inthe diploid and tetraploid maize. The results of this studysuggest that the amount of endopolyploid observed in maize genotypeshas an effect on their overall agronomic performance under thefield conditions.Copyright 1993, 1999 Academic Press Zea mays L., maize, endopolyploidy, diploid, tetraploid, flow cytometry     

Historical distribution and regional dynamics of two Brassica species

Plants often show a patchy distribution. This can be related to the discontinuous distribution of environmental variables that define suitable habitat. Metapopulation theory suggests that additional patchiness may be caused by the dynamics of local extinctions and recolonisations. However, the contribution of these two mechanisms to explaining the observed patterns, and thus the applicability of metapopulation theory to plants remains controversial partly because population turnover may occur at long time‐scales not usually covered by ecological studies. We analyzed the role of environmental variation and population turnover in determining the distribution of two Brassica species, an annual and a perennial, along 44 km of coastline in Dorset, UK. Mapped occurrence and abundance of both species in recent years was compared with distributions from a 70 yr‐old dataset and a survey of present‐day environmental parameters. Abiotic and vegetation parameters were correlated with the occurrence of both species in binary logistic regression models and explained spatial auto‐correlation in the Brassica distributions. These regression models suggest that neither species is occupying all potential habitat in the region studied. The relationship between historical and present distributions differed between the species. While an historical signal was very weak in the annual B. nigra, it had a large influence in predicting the present distribution of the perennial B. oleracea. This suggests local extinction and colonisation events for B. nigra over the 70 yr period, but not for B. oleracea which showed little evidence of population turnover. Our results demonstrate that the consideration of large time‐scales can reveal patterns of regional dynamics. We conclude that metapopulation dynamics might be possible for our annual but can be ruled out for our perennial study species over the past 70 yr. We argue that beyond this time‐scale possible metapopulation dynamics may be overridden by faster processes of environmental change.     

In vivo studies of gene expression via transient transgenesis using lipid-DNA delivery.

As the sequencing of the human genome proceeds, the need for a new screen for in vivo function is becoming apparent. Many investigators are turning to various transgenic models as a means of studying function. However, these approaches are very time consuming, with a transgene-expressing mouse model often taking months to establish. We have developed an efficient system for delivering genes in vivo, which allows the gene product to be studied as early as 24 h after introduction into the mouse model. The delivery system employs a novel cationic lipid, 1-[2-(9-(Z)-octadecenoyloxy)ethyl]-2-(8-(Z)-heptadecenyl)-3- (hydroxyethyl)imidazolinium chloride (DOTIM), and a neutral lipid, cholesterol, complexed with an expression vector containing the reporter gene chloramphenicol acetyl transferase (CAT). After a single intravenous injection of these complexes, several tissues were seen to express the transgene. High, persistent expression in the vascular endothelial cells in the mouse lung was obtained. Delivery of DNA in vivo has been evaluated by quantitative polymerase chain reaction and protein expression by CAT activity assays. In vivo studies showed reproducible expression in more than 500 mice injected via the tail vein. An early peak of expression was followed by lower, but sustained, expression for > 50 days. Transgene expression of CAT could also be identified by immunohistochemistry staining in mouse lung and appeared to be located within the capillaries. The pattern of in vivo expression could be modulated and targeted to specific organs by altering the lipid-DNA formulation. New expression vectors with altered introns and polyadenylation sites further improved expression. The expression reported here may be sufficient in magnitude, duration, and flexibility to be an attractive alternative, in some cases, to establishing transgenic animals by stable gene transfer.