|Andrewartha, K - LATROBE UNIV. AUSTRALIA|
|Stone, Bruce - LATROBE UNIV. AUSTRALIA|
Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 31, 1996
Publication Date: N/A
Technical Abstract: Lignin is a macromolecule polymerized in wall matrices of fully expanded cells to provide structural strength. Other wall components can become crosslinked to lignin either through passive (addition to quinone methides) or active (free radical addition) mechanisms to form large complexes. Characterization of lignin complexes provides insight into factors that regulate their formation. Isolated and ball milled walls from alfalfa (Medicago sativa, Siriver) stems were twice extracted with hot SDS (2h 90 C). SDS extracts (10-15% of the walls) contained between 40-60% lignin depending upon the maturity of the stem material. Chromatography on Fractogel HW-65 produced three fractions: F1(75-200kD), F2 (40-75kD), and F3 (10-40 kD). Neutral sugar compositions (molar ratios) of F1, F2 and F3 were similar, each containing xylose (0.5-0.6), arabinose (0.1-0.2) and glucose (0.1-0.3). Fraction 1 and F2 contained the highest proportion of protein and lignin while F3 contained mostly carbohydrate. Lignin analysis of F1 and F2 revealed guaiacyl (0.5-0.6), syringyl (0.3-0.4), and p- hydroxybenzaldehyde (0.1-0.3) units. Treatment of F1 and F2 with trypsin/chymotrypsin did not result in significant degradation of the lignin complex. Analysis of the proteins in F1 and F2 indicated that the amino acid composition and molar proportions were similar to initial wall preparations. It would appear that the proteins involved in these complexes were not specifically structural proteins but rather other wall-bound proteins such as peroxidases and hydrolases.