27 November 2015
The chemical battle between plants and insects
A new research paper by Copenhagen Plant Science Centre scientists clarify how some insects can sidestep the toxic defence mechanism of plants. The paper was recently published in the journal Insect Biochemistry and Molecular Biology.
Toxins are used as a defence mechanism by plants
Plants - being sedentary - have to defend themselves against insect herbivores with the use of chemistry. Some plants have a two-component defence system: a cyanogenic glucoside and a hydrolytic enzyme lay separated within the plant cell or a tissue. When the plant tissue is damaged, the compartments are mixed, and the enzyme degrades the cyanogenic glucoside, releasing a toxic substance.
Insects can overcome plant toxins in different ways
A variety of insects species can actually tolerate this chemical defence, in a number of different ways. This is asserted in the article Metabolism, excretion and avoidance of cyanogenic glucosides in insects with different feeding specialisations by S. Pentzold, M. Zagrobelny, N. Bjarnholt, J. Kroymann, H. Vogel, C. E. Olsen, B. L. Møller, and S. Bak, in the journal of Insect Biochemistry and Molecular Biology. The publication argues that insects use the following mechanisms to overcome the toxic compounds:
- They let them pass through the body intact.
- They break them down to other products (metabolizing them).
- They avoid uptake altogether.
Leaf-snipping is one way of overcoming the plant toxin
The Lepidoptera (an order of insects that includes moths and butterflies) snip of well-defined fragments from whole leaves. These fragments pass through their digestive system and are excreted intact. Thus, the two-component defence system is not activated.
An alkaline gut might also prevent toxification
Insects with a slightly acidic gut become intoxicated after consumption of some plants with a chemical defence mechanism. In contrast, insect species with an alkaline gut has been shown not to be affected in the same way. The authors suspect that the process of releasing the toxin is inhibited by the alkaline environment.
If you want to read more on this topic you can visit Section for Plant Biochemistry at Department of Plant and Environmental Sciences and VILLUM Research Centre for Plant Plasticity at University of Copenhagen.