Osmosis 20,Spring 2001

OSMOSIS 20,SPRING 2001

Contents

Director's Letter
Workshop Calendar
Plants in Action . . . SAPS goes wild in Wales
Holly leaves - themes and variations
Student Sheet 21. Investigations with duckweed (Lemna minor) - Estimating the number and biomass of a population of plants
News from SAPS Scotland
Schoolteacher Fellowship in Plant Science at Cambridge
Assaying peroxidase activity in plant tissues
Stomatal impressions – some simple alternatives

Letter from the Director

Dear Colleague,

Good ideas often start in a small way. When Richard Price became the first Director of SAPS, over 10 years ago, probably nobody could really envisage the extent to which SAPS ideas would grow and ramify into classrooms all over Britain and indeed (mainly through the website) into the world beyond.

By now you know that Richard retired last autumn - earlier than intended, but as a result of the ill health that has, in recent years, increasingly hampered his activities. If we look back to the early inspiration of fast plants, through a miscellany of film cans or the plastic bottles of supermarket science, to the more elegant molecular biology and ELISA kits, we can see the sharing of a wealth of ideas - some simple, others more sophisticated. Perhaps the key message from SAPS is that the ideas work in the classroom, that they promote good science teaching and encourage a real interest in plants. The network of SAPS extends far (with over 4000 on the OSMOSIS mailing list). Many teachers, young and not so young, have been inspired by attending SAPS workshops and passed their enthusiasm on to their students. Over the years Richard has given encouragement and support to many teachers and in turn we are grateful to these teachers for their contributions to the SAPS network and in helping SAPS become a significant influence in education.

I am sure you will all join me in wishing Richard happiness and better health in his retirement and in saying a big thank you to him for creating SAPS and all that it now stands for.

Erica Clark
Acting Programme Director

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Plants in Action . . . SAPS goes wild in Wales

Deep in the heart of rural Carmarthen in West Wales, wonderful things are happening! The first national botanic garden to be built in the United Kingdom for over 200 years opened to the public in May 2000. In the first nine months we have welcomed over 190,000 visitors - almost 10% over our target for the first whole year.

The centrepiece of the National Botanic Garden of Wales is the Great Glasshouse, the largest single-span glasshouse in the world. This huge ellipse, of glass and steel, houses thousands of plants from Mediterranean regions around the world - Chile, California, South Africa, Western Australia and the MediterraneanBasin itself. Here the living collections make even the most blasé students take notice - two hundred year old grass trees from Australia which thrive after a bush fire, exotic kangaroo paws pollinated by birds, plants that have perfected buzz pollination (no point in wasting valuable pollen on the wrong type of insect), seeds which plant themselves . . . we could go on.

Set within a 568 acre estate the garden dates from the late eighteenth century. It includes a variety of native Welsh habitats (broad-leaved woodland, meadow grassland, lake and stream) as well as some formal gardens. The Wallace Garden, named after Alfred Russel Wallace (the Welsh naturalist, linked with Darwin in the development of the theory of natural selection), is dedicated to the history of plant breeding and genetics. Some unusual 'back of house' features are accessible to the public - a biomass boiler which burns wood to heat the glasshouses and the 'Living Machine' to treat sewage through reed-bed technology.

Since opening last May, the education team has welcomed over 5,500 school, college and university students to the education programmes. Themes have included Plants in Action (linked to the science area of the national curriculum), Wonderful Water (habitats and ecology, linked to science) and Everyday Choices - the sustainable development trail (linked to science, geography and PSE). Each programme is available at Key Stages 1, 2, 3, 4 and A level and the majority are in English and Welsh. Our youngest learners were three year olds, and we have hosted A level groups for fieldwork and plant physiology sessions. We also organise specialist talks and tours for university students.

We have run over 20 INSET days, including primary and secondary SAPS courses, and plan many more this coming year. As an ex-head of science, I regularly used SAPS materials and tips from Osmosis as a starting point for class practicals and individual investigations. I'm keen to pass on the wealth of good ideas to teachers who may not be yet involved. So, why not find out more about our new education programmes and INSET days for Spring and Summer 2001 and the next academic year! Visit our website or better still, visit us! You can ring direct to education on 01558 667150 to request more information, or to book for groups.

Chris Millican
Head of Education
NationalBotanic Garden of Wales

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Holly leaves - themes and variations

Why does holly have prickles? In the New Forest, ponies graze holly eagerly, prickles no problem. They even bite off branches, let the leaves go soft for a few days then come back and munch them.
The foresters pollard holly as a winter food for ponies. Is spikiness something to do with being evergreen (e.g. Mahonia)? Slugs do not eat whole holly leaves but will if the prickles are cut off.

How many prickles on a holly leaf? Well that's easy - it's about seven isn't it, with a point at the top and three spikes either side! This simple thought can lead you into a number of useful activities with young pupils.

First try this with a group of pupils (adapt as appropriate for their age). "Imagine a delicious looking Christmas pudding. You are just about to take a little pinch thinking no one will notice . . . then you see the holly leaf decorating the top of the pudding. You pick up the (pretend, imaginary) holly leaf. With your eyes closed count how many prickles there are, up one side to the top and down the other side and keep the number secret for a moment."

You can then do a verbal bar chart. When you call out a number the children reply if it's the same . . . ones, twos, threes etc.

The next step is to find a real holly tree and look at the leaves. They are often on the ground but even though they are prickly they aren't too tricky to pluck from the tree. Hold the branch carefully then pinch a leaf from topside and bottom and pull it off towards the tree. If each child picks a leaf, counts and then finds others with the same number of prickles, they can make groups in order. Or with even more madness, each child has a number (say 0 to 30, or as many as there are in the class). Everyone picks lots of leaves, one at a time and gives their leaves to the person with the right number. After 10 minutes or so, stand back in line and count each child's pile of leaves. There will probably be lots (and lots) of shouting! Maybe try a number card stuck on children (or wash-off felt tip on forehead).

Going a bit further . . . Make a numberline zigzag book by joining (and weatherproofing with tackyback) squares of card, numbered 0 to 30 (in order).

This folds up easily and stretches 4 m or so on the ground. Now choose 3 or 4 chart builders to stand on one side of the chart. The other class members visit a nearby holly tree to pluck a single leaf. They count how many prickles on that leaf and return to the number line (not crossing or disturbing the line). The chart builder then carefully places the leaves in a line on the ground above the appropriate number, 7 prickles over seven, 12s over twelve and so on.

Two potential problems are pupils' feet knocking the line and leaves, or the wind blowing the leaves away. The pupils go on collecting one leaf at a time (swap chart builders occasionally) until the longest line has 15 or so leaves and a 'good looking' shape has appeared.

Circle the children around the graph. Just in their heads (not out loud) can they work out the following? Which number on the number line has the longest line over it? What is the lowest number . . . and the biggest number that has leaves over it? What does this graph tell us about holly leaves that we didnít know before? Now let them share their thoughts. How can they use averages or means to describe the chart?

Of course the shape of the graph is variable, often with peculiar surprises . . . a New York skyline, a bell or a profile of the Mendips? It is not always easy to put together a good sentence to describe the results. The longest line is usually in the teens (but discover where yourselves).

Here are some more ideas they could follow up and make charts to show what they find.

leaves from the ground only (even evergreen leaves drop off)
leaves from different trees (say from male and female trees - both have flowers but only the female has berries)
leaves from variegated trees (usually female and a bit more prickly)
Are leaves left and right handed? If it has seven prickles, are there four on one side, two on the other and always one on top?

More variations on the theme . . . As you do these activities, you may notice tunnels of leaf miner caterpillars eating the inside of the leaf. Some of these may have been torn open (by blue tits and great tits) but some have little round holes where the insect emerges. A smaller than normal hole shows that a parasitic wasp has got to and eaten the leaf miner - again good graphing data.

If you have a wooden fence with upright planks, chalk a number line (0 to 30) along the bottom.

As pupils bring a holly leaf, staple gun it to the fence over its number. A wonderful real life outdoor, interactive chart, which looks fine for a few months. A bit more standard is not pick leaves but, at record stations, to fill in little empty charts as the pupils return to tell the number of prickles they have just counted.

Consider fair tests, do they go for the most or least prickly, are they counting accurately, or choosing leaves randomly, or not recounting the same leaf? All the leaves are being picked at the height of the children so this activity will generally not show variation with height.

Holly is a poisonous plant and this should be well emphasised, but I would not be concerned at handling leaves or even berries. Remember, if you do wish to remove leaves from a tree, ask permission from the owner first. Picking leaves will not damage the tree - in fact, it will probably be all the bushier the following year. You will find more suggestions for investigations with holly leaves in OSMOSIS 16.

© Chris Townsend
Minstead Study Centre

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Schoolteacher Fellowship in Plant Science at Cambridge

We are pleased to offer a SAPS Schoolteacher Fellowship in Plant Science at RobinsonCollege, Cambridge. It is open to teachers in UK secondary schools and colleges. The successful candidate will be expected to carry out research into ways of enhancing the teaching of photosynthesis at secondary level. Part of the research will look at teaching and learning, focussing on conceptual difficulties faced by pupils and how best to encourage learning and understanding of photosynthesis within the curriculum. The research will endeavour to develop appropriate approaches to the teaching and practical investigation of photosynthesis, for pupils at KS3, KS4 and post-16 students. The Fellow will be expected to make major contributions to SAPS publications on photosynthesis.

The Fellowship is available for one full term at a mutually convenient time (in the year 2001-2002). Single accommodation in College and a meal allowance will be provided. The full cost of the successful candidate's salary for the term and a grant for consumables will be met by SAPS. Closing date for applications: 12 March 2001. Further information from: The Senior Tutor's Assistant, RobinsonCollege, Cambridge CB3 9AN (tel: 01223 339123).

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Assaying peroxidase activity in plant tissues

Peroxidase is believed to play roles in auxin catabolism, formation of lignin, cross-linking of glycoproteins in cell walls, as well as destruction of, for example, hydrogen peroxide.

As a link with possible investigations with Lemna (see Student Sheet 21) this protocol offers a rapid technique for extracting and making quantitative measurements of peroxidase enzyme activity. A variety of peroxidases are present in plant tissues. Peroxidases are strongly inducible - various forms of stress (chemical, mechanical, infection) cause elevated levels in the plant tissues. In this assay we measure ‘guaiacol peroxidase’, so called because it catalyses the formation of a red compound (tetra-guaiacol) from colourless guaiacol. The formation of this product can be monitored with a colorimeter.

Extracting the enzyme

Add 0.5 g of tissue to a cold mortar (placed in iced water before the lesson) with a pinch of silver sand. Add 5 cm3 of cold extraction buffer [sodium phosphate (pH 7.0) kept in a refrigerator until lesson] to the mortar. Grind the sample vigorously to produce a ‘clear soup’ with no visible fragments. Fill up a labelled microcentrifuge tube with the extract and cap it. Keep on ice until required. For another tissue sample, rinse the mortar and pestle and repeat the extraction procedure.
Place the microfuge tube(s) in a microcentrifuge (or ordinary centrifuge) and spin at high speed for 1 minute. Label a test tube, and in it place 9.8 cm3 of extraction buffer and 0.2 cm3 of the supernatant in the microfuge tube. This is your working enzyme solution. Keep it on ice until required.

Assaying the peroxidase activity

[Chemical Hazard]

The substrate solution is 0.125% H2O2 (v/v) solution in sodium phosphate buffer (pH 6.0) with 0.2 % guaiacol (v/v), kept at room temperature. Add the substrate solution to a colorimeter tube/cuvette to set the absorbency reading to zero. Use a blue filter in the colorimeter.
Then add 4.5 cm3 substrate and 0.5 cm3 enzyme solution to a clean colorimeter tube. Place it in the colorimeter and record the absorbency readings at 15-second intervals for at least one minute. If you wish to assay another sample, or to repeat readings, rinse the same colorimeter tube with tap water [WEAR GOGGLES]. Re-use the same tube as described above.
Plot a graph of absorbance versus time. The gradient of this line gives a measure of enzyme activity (in absorbance units per unit time).

Discussion points

What should be done if the peroxidase activity is too great, and the reaction is almost complete by the time the tube is placed in the colorimeter? What should be done if the peroxidase activity is too little?
Why does the reaction produce a constant gradient in the first minute or so, but form a plateau later on?
Identify the major sources of error in the protocol. Suggest why the initial extraction is done using cold buffer.
Why might stressed plants need higher levels of peroxidase than unstressed ones?
List a range of stresses to which plants might be sensitive, and for each, suggest an appropriate experimental protocol to investigate whether your suggestion is correct.
It has been reported (1) that Lemna minor fronds respond to oxidising pollutants, such as copper sulphate ions, by increasing their levels of guaiacol peroxidase. This happens within 24 hours of the addition of the ions to the water in which they grow. How might you investigate the effects of copper sulphate concentration on peroxidase induction? Or how could you compare the responses (peroxidase levels or growth) of other species of duckweed (1,2) to copper sulphate (or other metal) ions?

If you attach a computer, data-recorder or chart-recorder to the colorimeter, a continuous record of the progress of the reaction can be made, and then analysed by software. If you have a spectrophotometer, take readings at 470 nm to obtain a more accurate set of data, over a wider range of absorbencies.

Roger Delpech
Haberdasher's Askes' School

References:

(1) Teissure H, Guy, V Copper-induced changes in antioxidant enzyme activities in fronds of duckweed (Lemna minor) Plant Science 153 (2000) 65-72

(2) The charms of Duckweed website

The BSBI Education Initiative

The National Curriculum provides little opportunity for teaching plant identification yet there remains a need for competent field botanists. Careers requiring such skills include forensic science, wildlife conservation, ecological consultancy and even ecotourism. The Botanical Society of the British Isles (BSBI) depends on field botanists to undertake the surveys which provide knowledge of changes in our flora. The four areas outlined below (A, B, C & D) are part of the BSBI 'Education Initiative' contributing to training future field botanists.

Arousing interest - A website key is being developed to encourage wider knowledge of trees and shrubs prominent in our rural landscape. It will include 80 common native and introduced species in the British countryside. A beginner should be able to use this key to identify, and obtain further information on, an unknown tree or shrub. It will also include a glossary and information on botanical societies, books and courses.