Tiptoe through the tulips

Scientists have discovered that plant leaves activate defence mechanisms against plant eating insects within twenty seconds of an insect walking across them. Dr Alan Bown will be presenting the results of his footsteps research at the Society for Experimental Biology conference on Tuesday 9 April.

Dr Bown and colleagues studied the effects of insects traipsing across leaves, observing the chemical responses in the leaves over time. Ten seconds after larvae had crawled across the leaves, superoxide was released. In leaves superoxide is a recognised defence mechanism against attacking pests. Within twenty seconds, chlorophyll fluorescence was triggered Both these responses result in a trail of footprints across the leaf.

After five minutes, the plant has increased its levels of gamma-aminobutyric acid (GABA). GABA is known to inhibit neural transmission in animals, and is thought to function as an inducible plant resistance mechanism against herbivores.

The results are of particular interest because they demonstrate defence mechanisms that are triggered even when the plant is not wounded. Prevailing models show that plants synthesize wound-induced defence proteins and chemicals several hours after being attacked. In contrast, Dr Bown`s research shows a similar, though more rapid response when insects simply walk across the leaves.