Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/28/2002
Publication Date: N/A
Citation: Interpretive Summary: Fiber (cell walls) is a critical component of forages and is mainly made up of carbohydrates, protein, and lignin. It provides plants with structural support needed for normal development. Fiber is a source of digestible energy for dairy cows and it is critical for maintaining good animal health. However, the animal can only utilize the carbohydrate and protein fractions in fiber. In grasses such as wheat, cross-linking lignin to carbohydrate by ferulic acid limits digestibility of the fiber. When pathogens such as rust infect wheat leaves, the plant responds by producing more lignin and increasing the amount of ferulic acid cross-linking. This defense response helps to limit the spread of the disease. However,increased lignin and ferulic acid cross-linking will also decrease fiber digestibility. This work indicates that disease resistant varieties of forages would benefit dairy farmers as long as the disease resistance was not dependent upon the production of a highly lignified and cross-linked cell walls. Such plants may be quite healthy, but would also have limited digestibility.
Technical Abstract: Plant cell walls are dynamic structures that undergo specific remodeling events during plant defense responses. Changes in the coordinated partitioning of carbohydrates between the cytosol and the extracellular milieu may direct sheath cell wall remodeling that occurs in a wheat-endophytic interaction with a Fusarium proliferatum (F.p.) species. Increased levels of apoplastic myoinositol and glucose were apparent in the endophyte-positive F. p.-infected sheaths from asymptomatic greenhouse-grown wheat. The F. p.-infected plants exhibited a resistant-like response under conditions of host stress. Cellular concentrations of galactinol, glucose, fructose, sucrose and melibiose increased in wheat sheaths infected with the F. p. species compared to the non-infected control sheaths. In addition, the symptomatic F. p.-infected plants showed increased accumulation of arabinogalactans, syringyl lignin and ferulate dimers in the sheath epidermal walls in contact with the endophyte. These were distinct from the carbohydrate, lignin and ferulate deposition patterns in the non-infected control sheaths. Further examination of sheath walls in F. p.-infected and control wheat using laser scanning confocal microscopy revealed a distinct spectral emission profile localized to the epidermal walls in F p.-infected plants that was concomitant with the enhanced deposition of wall-bound ferulates. Increased levels of total ferulate dimers, particularly the 8-O-4 and 5-5 linkages were found in the F. p.-infected compared to control sheaths. These results indicate that even mild infection of grass cell walls with specific types of pathogens result in responses that could lead to decreased digestibility of the cell wall.