[This was written by Fran Siebrits and published online by Wild Magazine http://www.wildcard.co.za/, 2011]

The familiar saying “He who laughs last, laughs the loudest” applies to plants in their ability to survive as a species, even after they have been eaten!

Instead of repelling herbivores in order to survive, some plants produce an enzyme which has devastating effects later on in the stomach, once the unassuming herbivore has eaten its fill.

Plants produce an enzyme known as TD1 (threonine deaminase) which assists in certain metabolism processes such as degrading nutrients. The need for protection against herbivores such as caterpillars has resulted in the production of a closely related enzyme, TD2. Recent research has shown that plants use this enzyme to ‘starve’ their attackers.
Just like us, caterpillars and other animals need certain nutrients (and enough of them) for survival. One of these nutrients is called threonine, which is obtainable to herbivores by munching on green leaves. However, as soon as a plant senses threat, it releases TD2 which is ingested by the obliviously happy eater. TD2 actively works on the nutrient threonine, degrading it so that it is no longer of any nutritional beneficial.
So by the time the caterpillar has satisfactorily filled its belly with green mush, it has little or none of the essential threonine nutrient. The caterpillar therefore starves due to lack of nutrients and malnourishment.
Interestingly enough, TD2 only starts working on threonine once the plant material has been eaten and is inside the caterpillar’s belly. It moves on from a plant once satisfied, leaving the plant to have the last laugh.
This research is not only important in understanding the interaction of species in their environment and the evolutionary process, but it can also be of assistance in the agriculture sector. By understanding the structural make-up of TD2 and other enzymes, there is the potential to develop pesticides through further biomimicry studies.
Source: E. Gonzales-Vigil, C. M. Bianchetti, G. N. Phillips, G. A. Howe. Adaptive evolution of threonine deaminase in plant defense against insect herbivores. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1016157108
Viewed online [http://www.sciencedaily.com­ /releases/2011/03/110329151456.htm]