Focus on research: biologist Michel Haring
Do you enjoy the smell of freshly mown grass and the scent of flowers in the garden? You’re not the only one. It may seem unlikely, but plants themselves are also able to smell. For plants, however, it’s not a question of enjoyment but a matter of survival. Biologist Michel Haring carries out research on plants that are able to smell. The new greenhouse complex at Science Park Amsterdam, equipped with the latest gadgets, will be a great asset to his research. The new greenhouse complex at Science Park Amsterdam was opened on 28th June. “The greenhouses are equipped with the most recent climate-control techniques, which are indispensable for the top research on plants being carried out in Amsterdam’, according to Michel Haring. He is of the opinion that the city should not only be renowned for ‘that famous, green, hallucinogenic plant’, but that it should also show off the excellent plant research being carried out. He established The Amsterdam Platform for Plant Science in order to make all plant research in Amsterdam more visible to the public at large.
This platform will, for example, organize meetings in the field of plant biology for industry, students and research groups at both the VU and the UvA. ‘This will facilitate mutual contact as well as providing external promotion for the plant research being carried out in Amsterdam.’ According to Haring, such a platform is really necessary: ‘whenever plant research in the Netherlands is mentioned, people talk about Wageningen - and to a large extent that is, of course, true. However, the scientific plant research being carried out at Amsterdam is top research; it is unfortunate that people don’t realise this and we aim to change their perspective.’
The platform was Haring’s own idea. ‘There was already a strong collaboration between both universities in Amsterdam, and the collaboration between IBED (the Institute for Biodiversity and Ecosystem Dynamics) and SILS (the Swammerdam Institute for Life Sciences) is becoming increasingly intensive. We wanted to make this collaboration more visible, to show that we’re not all separate islands but that we are profiting from each other’s knowledge and expertise.’
Haring is professor of plant physiology. He investigates signal transduction in plants, i.e., the signals plants receive, how they receive them and what they subsequently do with these signals. This research is carried out at various levels: from the level of the single cell up to that of the whole plant. At cellular level, he investigates which signal-chemicals are present in the cell’s skin - its membrane. A plant membrane consists of a number of different lipids, some of which have a signal function, especially fatty acids. The cell can detect a change in the amount of lipids. ‘We humans have nerves. If you place your finger on a hot plate, you find out soon enough whether or not it’s turned on. How does a plant detect such matters? It has no nerve bundles, so each cell must detect for itself. All plant cells are, therefore, fitted out with appropriate sensors. We are trying to figure out the exact role played by lipids in this whole process.’
If you water a plant with salt water, or place it in a cold room or don’t water it at all, the plant will react. ‘Its cells become stressed. A cell is 99% water. If it becomes dehydrated and loses water, it needs to be able to do something about it. The cell must be able to measure what is dry and what is normal. The lipids in the membrane change shape or concentration when stressed. The cell detects this alteration by means of proteins that track this process, and the cell subsequently reacts. We are still unsure as to the exact process, but we are able to point out which specific signals occur in the plant. Our expert in this field, Teun Munnik, has been awarded a VIDI grant from NWO to investigate this process in detail.
In collaboration with Maus Sabelis’ research group at IBED, Haring is investigating the communication by means of odour between plants and insects. ‘By its odour, an insect can smell whether a particular plant is a suitable food source. If the insect subsequently begins to chew the foliage, enjoying a good meal, the plant produces new aromatic substances which attract enemies of this particular insect. We are now investigating what the plant actually does, what aromatic substance it produces and how it differentiates between e.g. a caterpillar chewing a leaf and a greenfly pricking into the leaf. Eventually it emits a different odour pattern so that a suitable enemy is attracted. Plants aren’t stupid!’
The fact that a plant is able to recognize its attacker is, according to Haring, of paramount importance to the survival of the plant species. ‘There are many very interesting evolutionary and ecological questions about this interaction which could be investigated, but what we would like to know is how the plant is able to detect that a red spider mite is present. One of the hypotheses is that, before pricking into the cell, the mite produces a little saliva to start the digestion process. The saliva contains signals which the plant recognizes: ‘Oh, there’s a mite eating my leaves’ because the saliva of e.g. a greenfly ‘tastes’ different. It may sound rather trivial, but saliva may be essential in recognizing different species of insect.’
Red spider mite saliva
However, herbivores aren’t easily caught. ‘If you examine a collection of red spider mites you will see that they all have different ways of dealing with the defence mechanism, e.g. the reaction of a tomato plant, which demonstrates the large degree of flexibility in a herbivorous population. They need to adapt to the reactions of the plant. The red spider mite tries not to give itself away - perhaps by omitting the substance by which the plant recognizes it in its saliva? There are red spider mite families whose saliva is less identifiable. Or perhaps the red spider mite adds something to its saliva which suppresses the plant’s reactions: the plant recognizes it, but is unable to transmit a signal. This is a new hypothesis which arose from the research carried out by PhD student Merijn Kant, who will receive his doctorate this month.’ Haring talks about the red spider mite and the tomato as if he were discussing an exciting football match. ‘In the case of the red spider mite, you would think that the plant doesn’t stand a chance, since the mite adapts constantly and so the plant would need to have the same kind of adaptability. And it would seem that this is actually the case: wild tomato varieties react differently’.
Plants have yet another secret weapon in their war on insects. ‘When a plant is being eaten by an insect, it produces aromatic substances to attract raiders. It turns out that plants in the direct vicinity, which are not yet infected by insects, are able to smell this and therefore activate their own defence mechanisms. A red spider mite won’t find a tasty meal on these plants, as the plants are aware that an insect is on its way, and also that it is a red spider mite and not a greenfly. I think this is really wonderful: plants can talk to each other, it’s truly spectacular! Just imagine: you’re walking through the woods enjoying the peace and quiet, and all the time the plants are talking to each other. When one tree is felled the rest of the wood is immediately aware that the woodcutter is in action.’
‘We are now able to identify a number of aromatic substances which, for example, attract raiders. We then try to see whether we can alter this by means of genetic modification, whether, for example, we can get them to produce fewer or even completely new aromatic substances, and whether this is of benefit to the plant. In collaboration with plant breeding companies, we formulate new ideas for improving tomato plants so that they are better able to defend themselves against all those herbivores lurking about out there.’
Haring also studies the petunia plant. His group investigates why the flower only produces scent at night. ‘If you look at it mechanically, a plant consists of a series of switch systems. We have discovered the main switch that can turn the scent on and off.’ Haring is attempting to regulate the production of scent in the petunia, and hopes to be able to influence the odour, and thereby also the taste of a tomato in a similar manner. ‘In the Centre for Biosystems Genomics, together with PRI Wageningen, we are trying to change the tomato into a product that will be more appreciated by the consumer than the present wasserbombe.’
‘My most important contribution to science to date is, I think, enabling that little bit of regulation of aromtic substance production. We started this work only five years ago and I am very proud of the group we have set up, in which really good researchers such as Teun Munnink and Rob Schuurink participate. We have achieved a certain status very quickly. Five years ago, I wouldn’t have dared to dream that we would have achieved so much already. And now we have the new greenhouses too!’
The new greenhouses comply with the most recent requirements: they have good temperature regulation, are completely watertight and have regulation systems. ‘The compartments are smaller and better separated, so that if we carry out an experiment using insects, they don’t spread through the whole greenhouse. Experiments with pathogenic fungi are truly reproducible in the new greenhouses. Instead of the old ‘cultivation greenhouse’ we now have a research greenhouse of top quality. Moreover, the design of the greenhouses is also lovely.’
Experiments on genetically manipulated plants will also be carried out in the new greenhouses. The complex consists of about fifty compartments divided into four types of greenhouse: ‘normal’ greenhouses, in which experiments are carried out on normal plants only; PK1, in which experiments on genetically modified plants are carried out, and PKM2 and PKM3, where work will be carried out on both genetically modified plants and genetically modified pathogens. Haring admits that some people are scared of genetic modification. ‘Some people are also scared of spiders. New technology often frightens people. This doesn’t go to say that we are not extremely careful.’ The greenhouses are well screened off. The pressure inside the PKM3 greenhouses is lower than the outside pressure. When you enter the greenhouse through the lock, the pressure outside is slightly higher than that inside, so that an inward draught is created and nothing can escape. Moreover, all doors in the complex are fitted out with a security system: only people with the correct key may enter.’
‘I myself also have reservations with regard to the commercial application of genetic modification. Much can also be achieved by means of classical breeding methods. I even believe that it is possible to feed the world with organic farming methods. But perhaps I am rather an idealist, as far as that goes’, says Haring, laughing. ‘I have never been tempted to eat a tomato from one of our research greenhouses. That is also strictly prohibited, although there is only an incredibly small chance that anything would happen if you did eat one of those tomatoes. If I am able to choose, I go for an organically grown tomato.