Chemical defense responses of upland cotton, Gossypium hirsutum L. to physical wounding

Authors: PARK, SANG-HYUCK - Colorado State University; Scheffler, Jodi; Scheffler, Brian; Cantrell, Charles; PAULI, CHRISTOPHER - Colorado State University

Submitted to: Plant Direct
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2019
Publication Date: 5/17/2019
Citation: Park, S., Scheffler, J.A., Scheffler, B.E., Cantrell, C.L., Pauli, C.S. 2019. Chemical defense responses of upland cotton, Gossypium hirsutum L. to physical wounding. Plant Direct. 3:5. https://doi.org/10.1002/pld3.141.
DOI: https://doi.org/10.1002/pld3.141

Interpretive Summary: Cotton (Gossypium hirsutum L.) secretes a number of chemical compounds that protect the plant from disease and insect pests. Some of these compounds are stored in glands that cover the cotton leaves and seeds. This study examined the response of the cotton plant to mechanical wounding designed to mimic wounding caused by insect feeding. The results showed that three protective compounds increased dramatically after wounding. Cotton also produces nectar which can be used to attract bees which feed on the nectar as a food source. Other beneficial insects such as ants are also attracted by the nectar and protect the plant from attack by other harmful insects and animals. Nectar has been reported to contain numerous other unknown compounds that may also play a role in plant protection. To better understand the nectar’s use and what happens when the plant is wounded, plants were mechanically wounded and then the composition of the nectar before and after analyzed. Out of 301 compounds monitored, 30 compounds were altered in response to the wounding treatment. Two of the altered compounds, have antioxidant and antimicrobial properties that may protect the nectar against pathogens. This study provides new insights into the wounding response of cotton plants.

Technical Abstract: Upland cotton (Gossypium hirsutum L.) secretes terpenoid aldehydes (TAs) that protect the plant from microbial and insect pests. Foliar TAs include plus (+) and minus (-)-gossypol, hemigossypolone, and heliocides. To examine foliar TAs’ response to herbivore-mimicked wounding, the four TA-derivatives were quantified by ultra-high performance liquid chromatography (HPLC). The results show that foliar heliocides increased by 1.7-fold in younger leaves after wounding. Upland cotton accumulates concentrated carbohydrates, amino acids, and fatty acids in foliar extrafloral nectar (EFN) to serve as a nutrient resource, which attracts both beneficial insects and damaging pests. To better understand the nectar physiology, particularly to determine the temporal dynamics of EFN metabolites in response to the mechanical wounding, a gas chromatograph-mass spectrophotometer (GC-MS) was used to perform metabolic profiling analyses. A total of 301 compounds were monitored, specifically 77 primary metabolites, 3 secondary metabolites and 221 unidentified compounds. The herbivore-mimicked wounding treatment changed the EFN composition and lowered overall production. The accumulation of 30 metabolites were altered in response to the wounding treatment and threonic acid levels increased consistently. GC-MS combined with Kovat’s analysis enabled exploration of EFN secondary metabolites including furfuryl alcohol and 5-hyrdomethoxyfurfural (HMF), which both have antioxidant and antimicrobial properties that may protect the nectar against microbial pathogens. This study provides new insights into the wounding response of cotton plants and which metabolites may have a role in triggering the plant’s defense mechanisms as well as highlighting some protective functions of secondary metabolites produced in foliar glands and extrafloral nectaries.