A recent talk given at the University of Sheffield by Harro Bouwmeester gave an fascinating insight into the secret life of parasitic plants. The word parasite commonly brings up images of fleas, ticks and worms but parasitism is also rife in the plant kingdom. Parasitic plants can have a large effect on crops, causing devastating effects particularly in poorer third world farming communities.
Some plant parasites, such as Witchweed and Broomrape, have evolved to become completely dependent on the plant which they parasitise and these parasites are unable to survive in absence of a host. Parasite seeds often remain dormant for long periods of time, only germinating if a potential host plant is nearby. The parasite then grows through the soil towards the host plant and attaches to the roots of the plant, before piercing the host root and obtaining nutrients through this attachment.
Scientists, from Wageningen University in the Netherlands, discovered that parasitic plants can recognise certain chemicals released by roots of potential host plants. This group of plant hormones, named strigolactones, allow parasites to detect and locate host plants so they can time germination and the direction of initial growth accurately.
Ironically, Strigolactones are released with the intention to attract assistance from a special group of helpful fungi. These fungi, which also attach to the plant root, provide critical nutrients from the soil in exchange for the carbon they take from the plant. Plants growing in soils which are low in nutrients such as phosphorus have a higher dependency on fungi partnership and so release higher amounts of strigolactones.
These findings have important implications for regions with low quality soil, such as areas of Africa, where striga is a major problem. Research into the production of strigolactones in plants is ongoing, but it appears that strigolactones may have a secondary function, making suppression of these chemicals in prevention of parasites difficult.
For more information: http://www.plantphysiol.org/cgi/content/short/139/2/920