OSMOSIS 16,AUTUMN 1999
Contents
Director's Letter
Workshop Calendar
Introducing ELISA
An appeal for feedback
Plant Pathology - Demonstrating Koch's Postulates
Brassica kits from Blades
Appeal to Teachers
News from SAPS Scotland
News from NCBE
Fold out identification charts, from Field Studies Council (FSC)
A simple and improved way for growing Mung Bean seeds
Differences between species
Postbag
Investigating variation in holly leaves
Letter from the Director
Dear Colleague,
Elsewhere in this issue there is news of the ELISA kit which we hope to launch in the autumn. Please get in touch if you would like to attend an ELISA workshop or if you would like to be trained to run ELISA workshops.
Those of you who use our web site will be aware of some changes there. John Hewitson of OundleSchool now looks after the site. We are introducing a special section for Scottish teachers. We have also increased the amount of reference material and of questions and answers. We welcome questions from students and teachers but please ask your students to search our database before e-mailing (or posting) their questions to us. The answer may already be on the web site.
This term we welcome Dr Leighton Dann of RoundwoodParkSchool, Harpenden as the first SAPS-Robinson College School Teacher Fellow. He will spend the term working in the lab at the UniversityBotanic Garden on a protocol to extract chloroplast DNA from plant material and to visualise it on the NCBE minigel electrophoresis system.
Richard Price
Programme Director
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Introducing ELISA
Some Osmosis readers have already attended workshops or been involved with trials while we were developing the SAPS ELISA protocol. Your comments and queries have been very useful in helping us to finalise the practical procedures and the documentation to go with it. The SAPS ELISA protocol has been developed for use in schools and colleges to detect the fungal pathogen Botrytis, which infects plant material, such as strawberries, raspberries, grapes, apples, tomatoes, onions, flowers and so on. The fungus is of considerable importance in relation to crop losses in the commercial world of horticulture.
So what or who is ELISA? . . . How can we use it in teaching? . . . and how is it used in the world of research and as a diagnostic tool? We live in a world of acronyms but ELISA is one that, once unravelled, is actually quite helpful.
The name stands for Enzyme-Linked ImmunoSorbent Assay and this immediately hints at what it is all about. The system depends on recognition, at the molecular level, between two molecules. We are familiar with these as the antigen and the antibody and so know that we are using a tool which depends on the mammalian immunological response. This molecular recognition is precise and specific so we have an elegant diagnostic tool which can detect 'foreign' molecules in plant or animal material. We can either accept it as such and see how this immunological response reaction can be applied to investigative work or we can use it as a means of enhancing understanding of immune system and its role in human diseases. The term assay implies that the system allows qualitative detection of specific molecules and it can also be adapted to give quantitative estimates of the particular antigen. The assay is highly sensitive and can detect extremely small quantities of the antigen.
The clue to the ELISA system lies in the 'sorbent' part of the name. It depends on the discovery that certain molecules (such as proteins, glycoproteins, lipopolysaccharides or complex carbohydrates) bind to polystyrene or clear plastic. A whole series of reactions takes place in small plastic wells, known as microwells. The antigen(s) to be assayed are first allowed to bind onto the surface of the well. The antibody which is specific for the particular antigen is then allowed to become attached to the antigen, which by now is held on the surface of the well. It will recognise only the 'correct' antigen, depending on its specificity.
The next stage is to introduce a second antibody and this one is linked to an enzyme. This antibody-enzyme conjugate is again specific for and will bind to the first antibody which detected the particular antigen. The enzyme is chosen to be one which allows an appropriate substrate to be converted to a coloured product. This whole series of reactions depends on the initial particular antigen being held on the surface of the well. If it is present, the reaction at the final stage is shown up as a coloured product. The intensity of the colour can be compared with known standards, or a prepared colour chart, to give a quantitative estimate of the particular antigen in the original material.
ELISA systems were first developed in about 1975 and are now used extensively in research and routine diagnostic procedures. In developing the SAPS plate-trapped ELISA kit, one priority was to reduce the time required for the series of reactions to be completed, so that meaningful results could be obtained within a short time scale, say within a 2 hour practical session. Procedures used in research may take up to 2 days to obtain the results.
The SAPS ELISA kit should be ready by the autumn 1999. As with other SAPS protocols and kits, contributions by teachers, working with their students, are an essential part of our development process. We send a grateful thank you to the ELISA guinea pigs.
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An appeal for feedback . . . we want data from SAPS investigations
The SAPS workshops are part of a chain reaction . . . a way of sharing practical ideas for teaching plant science, and initiating ideas that lead to good science investigations. Our trainers enjoy the enthusiasm and appreciation shown by many teachers attending the workshops and we hope, in turn, that this enthusiasm is passed on to their students. What we miss at SAPS is feedback from later stages in the chain. We would like to see some of the investigations that students do, whether it be a KS2 study, a project for A level or part of a PGCE dissertation. In particular, we would like to build up a collection of real data, obtained using fast plants, other plants, enzyme or DNA investigations. If you can dig out some of your students' work, done in class experiments or individual projects, we would be very pleased to hear from you. We may wish to incorporate some data or ideas for investigations into future publications, but we would, of course, seek your permission and agreement before doing so. Please contact us at the Head Office in Cambridge. Many thanks. We look forward to an overflowing postbag!
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Brassica kits from Blades
Complete Rapid-cycling brassica kits are now also available from Blades Biological, Cowden, Edenbridge, KentTN8 7DX, tel: 01342 850242, fax: 01342 850924).
The kit includes the updated SAPS documentation 'Investigations with rapid-cycling brassicas -Technical Guide'. This 36-page booklet describes how to grow rapid-cycling brassicas, gives ideas for investigations with an extension section covering genetics with fast plants. The booklet is provided with the kit or can be purchased separately.
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Appeal to teachers
We are always pleased to receive requests from your students for help with their projects and assignments. However, some students seem to think that we exist to do their research for them. For example, "For this assignment I need to find information on the factors affecting the biological production in plants with the use of photosynthesis. I hope that it is possible to send me this information." When we receive letters of this sort we respond by politely suggesting that, as a start, the students consult come standard post-16 textbooks for the information which they need.
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News from SAPS Scotland
Rodger McAndrew and his assistant Kirsty Menzies are based in the Institute of Cell and Molecular Biology in the University of Edinburgh, Darwin Building, King's Buildings, Edinburgh EH9 3JR. They can be contacted in the usual ways:
tel 01383 626077
fax 0131 558 8191
They will be glad to help with any enquiries.
Marjorie Smith is based at DollarAcademy, Quest Laboratory, Dollar FK14 7DU; tel 01259 743753, fax 01259 742867. Marjorie joined the SAPS Scotland team last summer and is continuing with her work on industry-linked biotechnology.
Over the past nine months the SAPS Scotland team have delivered 27 workshops to a total of 468 biology teachers and science technicians. The most popular workshops have been those involving Higher Biology practicals. Teachers have found these useful, especially for preparing for assessment of Outcome 3 (Collect and analyse information obtained by experiment).
In between workshops, the team are busy trying to prepare new material including experiments for assessment of Outcome 3 for the Advanced Higher.
Osmosis readers will be kept up to date with any major developments.
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NCBE News
Plant kit guides now on-line
Revised versions of the students' and technical guides from the plant DNA kit are now available on-line from the NCBE's website. The technical guide includes full recipes for all the buffers and other reagents used in the kit.
Food biotechnology
A comprehensive guide to food biotechnology, including media coverage in the UK, the legislation that applies to genetically modified foods and links to relevant companies, interest groups, reports and government agencies can be found at the NCBE website.
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Fold out identification charts, from Field Studies Council (FSC)
You may already be familiar with the range of useful resources produced by Field Studies Council and which give valuable support in fieldwork - for identification and when planning investigations. Their series of 'fold out' identification charts are proving to be very popular identification guides, with excellent keys for different groups of plants and animals including: plants common in woodlands, plants common on sand dunes, plants common on moorland, lichens and air pollution, lichens of rocky shores, waste grounds and roadside grasses. These charts, price £2.25 each, are available from Field Studies Council, Head Office, Preston Montford, Montford Bridge, Shrewsbury SY4 1HW (tel: 01743 850674, fax: 01743 850178) and from FSC Centres.
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A simple and improved way for growing Mung Bean seeds
Recently I have been getting fungal contamination when growing mung beans on vermiculite using the method described in Worksheet 14 and on the SAPS website. A simpler and more effective technique is to simply soak the seeds in water overnight in a shallow tray (eg cat litter tray - these are cheaper than white 'laboratory trays') using water to a depth of about 1 cm. The following day pour off the excess water and rinse twice with fresh tap water, then drain, leaving the seeds damp but not immersed. Repeat this each day for as long as is required for the seeds to germinate. Using this technique I have not had any contamination and have saved money on vermiculite! Take care not to lose seeds down the sink when pouring off the excess water. A simple strainer can help here. Barry Meatyard
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Postbag
Q. We cross-pollinated our fast plants hoping to grow a second generation. However the seeds were very small and very few of them germinated. What have we done wrong?
A. We think that the problem here is that the plants were removed from the capillary matting before the seeds had matured in some of the pods. The plants should be left on the capillary matting under the lights until the pods begin to turn brown. This normally is the signal that the seeds inside have reached maturity. If in doubt try removing one pod, drying it and examining the seeds. They should be the same size as those available from the suppliers (Philip Harris or Blades Biological).
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Differences between Species
Can you identify these leaves? All except one (ivy) were taken from trees. One of the trees is not a 'flowering plant' (which one?). The others are common in the British countryside.
Is each leaf typical of the rest you might find on the same plant, or is there variation within the species (see holly below)?
[Answers in next Osmosis]
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Investigating Variation in Holly Leaves
These leaves were taken from different places on a single holly tree, Ilex aquifolium.
There is one obvious way in which each of these leaves differs from each of the other leaves. What is this difference?
Find a holly tree and examine the leaves. If you wish to remove any leaves, remember to ask permission from the owner of the tree. The questions below may help you to investigate the variation you find.
1. Does a given leaf have equal numbers of spines on each side?
2. Some leaves may be flatter than others. Do flat leaves have more or fewer spines than leaves which are not flat?
3. Do large leaves have more spines than small leaves?
4. Does the number of spines on each leaf seem to be related to the position of the leaf on the tree?
5. Do old leaves have more spines than young leaves?
Design one or more tables which you could use to record your results. Then plot your data (figures) on a suitable graph. You might, for example, decide to plot number of spines per leaf against the height of the leaf above the ground. Do you find any pattern or trend in the results you have obtained?
You could then extend your investigation, perhaps by comparing data from several holly trees, growing in different places. Do you get a similar or different pattern in the variation?
Acknowledgements to Rodger McAndrew, Queensferry High School, Scotland.