DRACULA OR ROBIN HOOD? WAIT TILL YOU HEAR THIS....
Most plants make their own food. They are green as they contain a green pigment called chlorophyll. Chlorophyll is necessary for photosynthesis - a process in which plants harness the light energy from the sun and use it to produce food (sugars) from carbon dioxide in the atmosphere. No chlorophyll = no sugar! The sugars from photosynthesis and minerals taken up via roots from the soil make up plant 'diet'.
This is a haustorium clasping around a root of another plant (grass) and sucking out nutrients. It is around 1mm in diameter - the size of a grain of sand. The image to the right is a slice called section taken through the middle of the haustorium and stained with a dye called toluidine blue. The cells of the parasite stain purple and the cells of the grass stain blue.
Some parasitic plants - called hemi-parasites - are green. They produce their own sugars and steal water and minerals. Holo-parasites are not green and you know what that means! They don't produce sugar and have to steal all needed food (sugar and minerals) from their hosts!
HEMIPARASITES V HOLOPARASITES
YELLOW RATTLE (Rhinanthus minor) THYME BROOMRAPE (Orobanche alba)
All this sounds rather exotic, right? Nope. They are here! You can find NATIVE hemiparasitic plants in meadows, neglected lawns, pastures, along pathways, even in car parks! They look like many other herbs except they get up to mischief under the ground (most parasitic plants in Ireland connect their roots to roots of other plants). Just look at them in pictures above. Would you have guessed ? No, didn't think so!
So now that you know they are here, it must give you the creeps. Surely, it sounds sneaky what they do. Clandestinely latching on to their poor victims (otherwise known as hosts). Sounds like injustice. Nothing good could come out of it, right? Well, wrong again! Some parasitic plants can act as the Robin Hoods of grasslands. They steal food from dominant plants (usually grasses) that smother weaker ones (flowers and herbs) and, well, they don't give to the smaller ones but allow them to compete better with the bullies.
Grasses have been only quite recently bossing around in grasslands. Before the age of tractors, fertilizers and 'improved' seed mixtures, meadows full of flowers and buzzing with wildlife were a common sight. Grasses and herbs used to live side by side in colourful and diverse areas. The intensive farming of the past few decades involving fertilizers and silage production disturbs this balance and in effect colourful meadows and pastures have been largely replaced by plain green fields composed of very few species, mainly vigorous grasses. Meadows with a lot of wildlife in them remain mostly in areas which are too difficult to farm such as steep slopes of eskers (gravel ridges created by melting waters under glaciers) or on very wet ground (Shannon callows). Parasitic plants can help bring balance back to grasslands where small herbs are smothered by grasses.
Why do parasitic plants prefer some plants to others? That is the bit we are trying to understand in the lab. Plant cells are surrounded by cell walls that can form a barrier for the parasitic plant.
Different plants have different cell walls and therefore might differently react to the attack by the parasitic plant. We think we might be on to something here but it will take more research to be sure. Watch this space! In the meantime, the haustoria are being collected, cut into extremely thin slices and their cell walls stained with different dyes resulting in the beautiful images we will transfer onto tiles. Different cell walls stain differently. Pectins stain purple, lignins stain blue...hope all this made it clearer for you!
text and images by Anna Pielach
