The Feasibility of Using Autofluorescence to Detect Lignin Deposition Pattern during Defense Response in Apple Roots to Pythium ultimum Infection

Abstract

The molecular mechanisms underpinning apple root resistance to infection by Pythium ultimum have not been carefully investigated until recently. A panoramic and high-resolution picture of genome-wide transcriptional networks regulating the defense activation in apple roots was obtained recently from a comprehensive transcriptome analysis. Among the most notable transcriptome changes are the upregulation of phenylpropanoid and flavonoid biosynthesis, transportation of secondary metabolites, and laccase-directed lignin formation. However, assessing cellular responses and anatomical changes in young roots of apple as a woody species of the Rosacea family remains challenging. Taking advantage of the autofluorescence of lignin and the specific staining by Wiesner reagent, the feasibility of using microscopy to detect lignin deposition in apple roots was evaluated. The preliminary results indicated that a combination of brightfield and fluorescence images may provide the opportunity to reveal the location and degree of lignification in sectioned roots. The procedure represents a proof-of-concept of using fluorescence microscopy to examine cellular features relevant to apple root resistance traits. The ability to detect subtle phenotypic variations, such as lignin deposition patterns, is critically needed to bridge the gap between genomic data and macro-level plant resistance phenotypes and to further identify the resistance mechanisms of apple root.