Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2015
Publication Date: 8/20/2015
Citation: Baker, C.J., Mock, N.M., Smith, J.M., Averyanov, A.A. 2015. The dynamics of apoplast phenolics in tobacco leaves following inoculation with bacteria. Frontiers in Plant Science. 6:649.
Interpretive Summary: Bacterial plant diseases cause major damage to crops each year and the cost of controlling them adds greatly to production costs and often involves antibiotics which are a public concern. 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. The apoplast is much like the moat around a castle, protecting it from attack. The pathogen will produce molecules attempting to break or weaken the apoplast barrier, while the plant cell, once it detects the pathogen, will send out various molecules to fortify the apoplast and counter-attack the pathogen. In this manuscript we are reporting a procedure that allows insight into the chemical events in the apoplast between the pathogen and plant cells. In addition the procedure unexpectedly also provides an indication of the physical integrity of the apoplast barrier during this interaction. The leaf apoplast is highly vulnerable to manipulation either by genetic engineering or direct application of materials to leaves, via stomata or additions to ground water, and delivered by xylem. 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: This study demonstrates that the accumulation of apoplastic phenolics is stimulated in planta in response to bacterial inoculation. Past studies have shown that levels of extracellular phenolics are elicited in plant cell suspensions in response to bacteria, and that tomato plants infected with viroids showed changes in apoplastic phenolics. The method described here monitored changes in apoplastic phenolics following bacterial inoculation. Inoculation with a saprophyte, Pseudomonas fluorescens, was used to elicit phenolics and examine the effects of three variable parameters on phenolic composition. Location of the inoculation on the leaf, position of the leaf on the plant, and inoculum concentration were standardized for further experiments. The patterns of phenolic change in the apoplast were compared for tobacco inoculated with P. syringae pathovars, pv. syringae, an avirulent HR-causing pathovar and pv. tabaci, a virulent disease causing pathovar. Both pathogens elicit increased levels of the hydroxycinnamic acids, acetosyringone and acetovanillone, and in addition appeared to weaken the apoplast/symplast barrier, based on the dramatic increase in chlorogenic acid isomers normally found within the cell. This unexpected aspect will require further study of intercellular phenolics.