|TUMLINSON, JAMES - Pennsylvania State University
Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2017
Publication Date: 4/23/2017
Citation: Block, A.K., Vaughan, M.M., Christensen, S.A., Alborn, H.T., Tumlinson, J.H. 2017. Elevated carbon dioxide reduces emission of herbivore induced volatiles in Zea mays. Plant Cell and Environment. doi:10.1111/pce.12976.
Interpretive Summary: Variations in atmospheric conditions will likely impact American agricultural, thus threatening future supplies and food safety. To address and adapt to these expected conditions and provide a sustainable food source, it is vital to understand the impacts to agricultural commodities. Modeling predictions indicate a likely doubling of atmospheric carbon dioxide levels within the next 50 -100 years. Scientists from the Center for Medical, Agricultural and Veterinary Entomology sought to determine if high carbon dioxide levels affect how sweet corn defends itself against insect pests. To do this we compared the amount of airborne chemical signals (odors) produced by sweet corn grown at normal or high carbon dioxide levels when infested with caterpillars. Our study showed that under high carbon dioxide conditions sweet corn released lower levels of these odors from its leaves than it did under normal conditions. These odors help protect sweet corn from caterpillars as they act as locator signals for parasitic wasps, which use these plant-produced odors to find infested plants and lay their eggs in the caterpillars, thus killing them. These findings suggest that growers (particularly organic growers) that use such wasps as a form of biocontrol to reduce crop damage from caterpillars may need to modify their pest management strategies if atmospheric carbon dioxide levels rise.
Technical Abstract: Terpene volatiles produced by sweet corn (Zea mays) upon infestation with pests such as beet armyworm (Spodoptera exigua) function as part of an indirect defense mechanism by attracting parasitoid wasps; yet little is known about the impact of atmospheric changes on this form of plant defense. To investigate how atmospheric change affects indirect defense, we measured herbivore induced volatile emissions in plants grown under elevated carbon dioxide (CO2). We found that S. exigua infested or elicitor treated Z. mays grown at elevated CO2 had decreased emission of its major sesquiterpene, (E)-ß-caryophyllene, and two homoterpenes, (3E)-4,8-dimethyl-1,3,7-nonatriene and (3E,7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. In contrast, inside the leaves elicitor induced (E)-ß-caryophyllene hyper-accumulated at elevated CO2, while levels of homoterpenes were unaffected. Furthermore, gene expression analysis revealed that the induction of terpene synthase genes following treatment was lower in plants grown at elevated CO2. Our data indicate that elevated CO2 leads both to a repression of volatile synthesis at the transcriptional level and to limitation of volatile release through effects of CO2 on stomatal conductance. These findings suggest that elevated CO2 may alter the ability of Z. mays to utilize volatile terpenes to mediate indirect defenses.