Induction of apoplast phenolics in pepper (Capsicum annum) leaves in response to pathogenic bacteria

Authors: Baker, Con; Smith, Jodi; YARBERRY, ANDREA - Orise Fellow; RICE, CLIFFORD - US Department Of Agriculture (USDA)

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2020
Publication Date: 1/1/2020
Citation: Baker, C.J., Smith, J.M., Yarberry, A.J., Rice, C. 2020. Induction of apoplast phenolics in pepper (Capsicum annum) leaves in response to pathogenic bacteria. Physiological and Molecular Plant Pathology. 109/101453. https://doi.org/10.1016/j.pmpp.2019.101453.
DOI: https://doi.org/10.1016/j.pmpp.2019.101453

Interpretive Summary: Plant bacterial diseases cause major damage to crops each year and controlling them adds greatly to production costs. The plant leaf apoplast, which is the cell wall region just outside the plant cell itself, is the first line of defense against most aerial pathogens. This study demonstrates that a newly discovered plant defense mechanism, that was first described in tobacco, also occurs in pepper and may to be an inherent property of crop plants. The mechanism could be used to detect disease prior to symptom development and/or its components be enhanced for improved resistance. This information will benefit plant scientists and breeders who are devising new strategies to improve disease resistance in plants as well as decrease the use of chemical pesticides and antibiotics.

Technical Abstract: The objective of this study was to corroborate, in pepper, the response of tobacco to induce apoplast phenolics upon bacterial inoculation. Leaves of Bell peppers (Capsicum annum), 6 to 8 weeks old, were inoculated with bacteria and analyzed for apoplast phenolics after different periods of incubation. Pseudomonas syringae pv. tabacci, 108 cfu ml-1, induced numerous phenolics to accumulate in the leaf apoplast after 24h. While about 15 peaks were distinguished by UPLC-UV, only about 8 major peaks were closely followed. Using this bacterial isolate, it was found that all the fully developed leaves on a single plant had similar phenolic responses. Between plants, the response was also similar but had more variability. The response was proportional to the bacterial concentration. Water and P. fluorescens inoculated plants had very negligible responses. When pepper plants were inoculated with P. s. pv. tomato and pv. syringae, there were differences in the magnitude and composition of the phenolics. The increases of apoplastic phenolics generally followed the growth of the bacteria over a 48 h period. The apoplastic phenolic response described here for pepper, when inoculated with bacteria, is very similar to the response previously described for tobacco. The phenolics are different. The redox and bioactive properties of these phenolics remains to be determined.