OSMOSIS 3,SPRING 1992
Contents
The SAPS Interview
Carnivorous plants - part 2
Noticeboard and Your Questions Answered
Investigating seed germination
The SAPS Interview
HUGO's there? ARGO!
Most of us have heard of HUGO, the HUman Genome Organisation which coordinates a £2 billion world wide research programme to map all of the DNA in the human genome.
But how many of us have heard about the parallel programmes to map the DNA of other organisms including a plant? The plant is Arabidopsis thaliana (thale cress) which is a common weed of waste ground.
We spoke to Dr Mary Anderson, Director of the Arabidopsis Stock Centre in the Department of Life Science at NottinghamUniversity.
SAPS: Mary, perhaps you could start by telling us a little about the Arabidopsis programme?
Mary: Several countries including the UK have Arabidopsis research programmes. Although they are independent, collectively these programmes can be regarded as an Arabidopsis genome project which I like to call ARGO. One aim is to sequence the entire genome of the plant by the end of the century.
SAPS: Could you explain what is meant by 'sequencing the entire genome'?
Mary: The genome represents all the DNA contained within an organism. By chemical analysis it is possible to work out the order of individual bases (A, T, G and C) in the DNA. Analysis of the sequence of these bases will reveal regions of the DNA corresponding to genes and their controlling regions. By this means it is hoped to identify all of the genes that 'make up' a higher plant.
SAPS: Why choose a tiny weed, instead of an important crop?
Mary: Although Arabidopsis has no economic value, it has many characteristics that make it an ideal model system for understanding plant physiology and development.
SAPS: Could you give some examples?
Mary:Arabidopsis is a flowering plant and therefore functions like any other higher plant. It is very small so can be grown in large numbers in a small space. It also has a rapid seed-to-seed cycle of 6 - 8 weeks. This means that up to 8 generations can be grown in one year so genetic experiments are fast and convenient. Compare this to, say, maize which requires areas the size of football pitches to grow the necessary plants for analysis. Also, with maize, you only get one or, at the most, two generations per year.
SAPS: Does it have any other advantages?
Mary: Yes. The genome is very small - much smaller than the genome of any crop plant. In fact it is only 15 times larger than the genome of the bacterium Eschericia coli. In addition, Arabidopsis is diploid whereas many crop plants are polyploid which makes studying the genetic control of physiology and development more complex. By exploiting these attributes it will be quicker and easier to learn from Arabidopsis and then apply this to the improvement of crop plants.
SAPS: But Arabidopsis is a dicot and most of the important crops in the world are monocots. So why not choose a monocot with the same features as Arabidopsis?
Mary: The simple answer is because there isn't one. However recent advances in genetic mapping technology may mean that certain monocots will become amenable to rapid genetic analysis. Rice is perhaps the best candidate for this since it has a relatively small genome. But that is another story!
SAPS: What will mapping the genome actually tell us about plant physiology and how development is regulated?
Mary: Mapping the genome is only the start of the story. The sequence data from the genome project will give us the framework of genetic information which is necessary for a detailed study of the function of individual genes. Undersatnding the function of individual genes and their regulation will come from the study of mutants, either naturally occurring or induced in the laboratory. This is where Arabidopsis really comes into its own because the plant is so amenable to genetic research. It is easy to induce mutations and it has a fast cycling time.
SAPS: The Arabidopsis programme seems to be absorbing a lot of money which might be spent on other areas of plant science research. What are the likely benefits of all this knowledge about Arabidopsis?
Mary: The benefits of the Arabidopsis programme are quite far reaching. Not only will there be a greater understanding of the fundamental processes that regulate flowering plant development, but the potential for modification of crop plants will be phenomenal. Understanding the control mechanism of flowering could significantly increase the yield of several important crop plants.
SAPS: What part does the Nottingham Arabidopsis Stock Centre play?
Mary: The Stock Centre has a fundamental part to play in the ARGO programme. It acts as a repository for all the available Aracbidopsis germplasm. This is important for the long-term conservation of genetic diversity. This genetic diversity can be exploited by the ARGO researchers to gain an understanding of individual gene function and to look for better alternatives (alleles) of a gene, or new genes that can improve a particular characteristic of a plant.
SAPS: Could you give us an example?
Mary: One exciting area of research is the investigation of genes that confer resistance to fungal plant pathogens in crucifer crops such as oilseed rape.
SAPS: Does the Stock Centre at Nottingham contain Arabidopsis lines from Britain alone or do you have material from other parts of the world as well?
Mary: Many geographical races of Arabidopsis have been collected over the years from railway sidings in Leicestershire to mountains in Afghanistan. Thus a large amount of natural genetic variation is available and this will eventually be collected and documented at Nottingham. Similarly, the induced mutants produced by researchers will require safe keeping. There are already thousands of such lines scattered among the different laboratories of the world. Our aim is to make sure that these resources are not lost for future agricultural and genetic research.
SAPS: Arabidopsis sounds like a very interesting plant. In what sort of places might we find it growing in our surroundings here in Britain?
Mary: It is fairly common on dry soils all over Britain. Good places to look are banks, walls, hedgerows and waste ground.
SAPS: Could we grow it easily in schools?
Mary: Yes! Arabidopsis is as easy to grow as are rapid-cycling brassicas. However, the flowers are very small - much smaller than brassica flowers - and the seeds are like dust.
SAPS: Are there any other differences?
Mary: Yes. Unlike most lines of rapid-cycling Brassica campestris, Arabidopsis is self-compatibale.
SAPS: I see, with the brassicas we have to cross-pollinate the plants to get good seed set. With Arabidopsis the flowers pollinate themselves automatically. Surely that is an advantage?
Mary: Well it is and it isn't. It depends on what you want to do. If you want to grow lots of plants not having to pollinate them is an advantage. However, if you want to do some genetics, crossing some plants with others, then you must either emasculate the female parents by removing the stamens or use male sterile plants.
SAPS: Well thank you for all this information about Arabidopsis. Who could have guessed that a small weed could be the subject of so much interesting research!
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Carnivorous plants - part 2
Propagation
Drosera capensis (Cape sundew) and Dionaea muscipula (Venus fly trap) are easy to grow from leaf cuttings taken in April or May. If good lighting and high humidity can be maintained the plants will root quickly in the normal peat/sand 1:1 mix. Sarracenia purpurea (Huntsmans Cap) can be propagated by dividing the rhizome. Small specimens do well in large eco-column units.
Some ideas for investigations
Can a fly trap count? Does it have a memory?
Strange questions to ask about a plant? Examine 10 open fly traps. Do not touch them! Look for the trigger hairs. How many are there on each side of the trap? Is there the same number of trigger hairs in all 10 traps?
One of the most interesting questions about the fly trap is this. How does the trap know when to close and when not to close? For example, it will not close when a raindrop or a piece of debris falls on a trigger hair but it will when an insect does. It seems as if the trigger hairs must be touched more than once.
Use a very fine pin or needle and a stop watch to investigate this interesting problem. Here are some suggestions:
Touch 1 hair once and note the response.
Touch 1 hair twice in quick succession (e.g. 1 second)
Touch 1 hair twice with a longer interval (e.g. 1 minute)
Touch 1 hair once and then another hair on the same side once. And so on.
Fly trap digestion
Sometimes a fly trap will close on something which is not suitable 'food' e.g. a soil particle. If this happens it will open again without trying to digest it. How does it know what to digest?
You can investigate this by placing small quantities of different substances in closed traps and seeing if they open.
What sort of substances are likely to be effective? Remember that fly traps grow in soils deficient in one particular mineral.
Nigel Stevens
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Noticeboard/Your questions answered.
SAPS in Spain
Dr Liuis Torres writes: I work in Barcelona at the Natural Science Resources and Experimentation Centre which belongs to the Ministry of Education of the Catalonia Government. Among other activities we provide teachers with free teaching materials for 12 - 18 year olds and suitable guidance fro practical lessons.
Last year we decided to expand our plant science section because we think that working with plants can be as exciting and useful for pupils as working with animals - and plants are obviously important and easily available.
An interesting article: "The place of plants in school science", Journal of Biological Education, 1987, 21 (3), 185 - 189, prompted me to write to the author, J N Honey, and to the ASE requesting more information about educational work in plant science. The answer from both was: get in touch with SAPS.
I was fortunate to go to Cambridge for one term to work with the SAPS team. From January to March 1991 I worked at Homerton with rapid-cycling brassicas. It was a fascinating experience and I learnt much which is very useful back here in Barcelona.
Q. Do I really need a light bank for growing rapid-cycling brassicas?
- Yes. A light bank is essential if you want the plants to grow properly. They also need a fairly constant ambient temperature of about 24 C. For further details see the Teachers' Guide and the Light bank Notes in the documentation with the Basic Kit.
Q. How close to the lights should the brassicas be?
- The tops of the plants should be within 5 - 7 cms of the lights throughout their growth. Schools have ingenious ways of maintaining this distance. Some start the plants off standing on blocks, etc., and then lower them as they grow. Others move the lights up, but this can be difficult. One of the best solutions is to hang the lights at an angle with one end nearer the bench than the other. The plants are then moved along as they grow.
Q. My brassicas grow slowly and they are straggly and weak with pale leaves.
- This effect is probably caused by a combination of insufficient light and low temperatures. Keep the tops of the plants close to the lights (see above) and monitor the temperature with a max/min thermometer. If the temperature drops below about 16 C at night growth will be much slower. Try covering the sides and ends of the light bank at night but take care to avoid over-heating.
Q. What else can I grow under my light bank?
All sorts of things! Here are some of the suggestions received from schools.
- Paul Ward (St. Ivo School) has grown delicious radishes in four weeks under the double light bank on his home-made trolley. He says that varying the number of fertiliser pellets clearly shows the effect of too little and too much fertiliser. One of his classes is studying inter-specific competition using carrot, lettuce, radish, beans and wheat - all grown under his light banks. He says "These kinds of experiments are particularly good for design and carry out investigations for GCSE."
- Another tip from Paul Ward. "Use white card all around the light bank. This gives a much more even illumination and reduces edge effects."
- Nigel Stevens (FrogmoreSchool) reports that carnivorous plants grow very well under his light bank.
- Several people report that Canadian pondweed, Elodea canadensis, and duckweed, Lemna minor, both grow very well under their light banks.
Q.Do I need to replace the tubes in my light bank?
- Yes. Older tubes produce less light (and more heat) than new ones. Here at Cambridge we replace our tubes once a year.