Elevated CO2 in atmosphere weakens defenses of soybeans

In research to be presented at the annual meeting of the American Society of Plant Biologists in Chicago (July 7-11, 2007), researchers will show that elevated CO2 may negatively impact the relationship between some plants and insects. Elevated CO2 is considered to be a serious catalyst of global change. Its effects can be felt throughout the ecosystem, including the insect-plant food chain link. Safeguarding highly-usable crops is of great importance to a number of local and national economies.

A number of plants have inherent enzyme-based defenses that are released during insect attack. This study observed that when soybeans (Glycine max) were exposed to elevated amounts of CO2 the plants became more susceptible to attack by Japanese beetles (Popillia japonica). Furthermore, as these beetles consumed the weakened soybeans, the insects invasive abilities were intensified.

Dr. Jorge Zavala, Sr. of the Institute for Genomic Biology at the University of Illinois, and colleagues conducted tests in which they reviewed this herbivorous attack-defense cycle. They studied soybeans grown in traditional field conditions but with additional exposure to ambient CO2. The results showed that the amount of cysteine proteinase inhibitors (CystPls) expressed in the genes decreased when soybeans were exposed to elevated CO2. CystPls is naturally produced by soybeans when they are under insect attack. It inhibits further attack once the invader has ingested it.

Our results suggest that elevated CO2 increased the susceptibility of soybean to invasive insects by down-regulating the expression of hormones related with defense, which down-regulate the important defense CystPls against beetles, Zavala said.

Zavala also explained, Under natural field conditions, elevated CO2 not only increased susceptibility of soybean to herbivory by the invasive species Japanese beetle, but also enhanced the performance of these beetles.

The investigation also determined the expression of genes that regulate two of the soybeans defensive hormones, jasmonic acid and ethylene. The results showed that exposure to increased CO2 lowers the plants ability to regulate its defensive hormones.

The relevancy of this study is far-reaching since soybeans are an important crop to a number of different economies. Furthermore, while this study is specific to one plant and insect pairing, these findings will help inform the on-going debate on CO2 exposure and global change.


Posted by: Erica    Source