|Macadam, Jennifer - UTAH STATE UNIVERSITY|
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 26, 2002
Publication Date: N/A
Interpretive Summary: Cellulose, hemicellulose, and pectin make up 30 to 60% of the leaves and stems of major feed crops. Due to their intimate association with lignin, and in some cases diferulates, only 50% of these polysaccharides are digested and used by livestock or are readily converted into industrial products like ethanol. Developing crops with low lignin and diferulate levels should improve polysaccharide utilization, but will crops grow normally? In studies with tall fescue (a forage grass commonly fed to livestock), we found that accumulation of diferulates in leaves was closely associated with slowing of leaf growth. Cessation of leaf growth coincided with the deposition of lignin into leaves. In future laboratory studies, we will manipulate the timing and quantity of diferulates and lignin deposited into leaves and stems to see if these components indeed control the growth of forage grasses as well as cereal crops like corn, wheat, or rice. These studies are part of a larger effort to identify potential benefits and pitfalls of manipulating lignin and diferulate deposition into plants. Further work is required to clearly demonstrate that diferulate cross-linking and ignification are agents responsible for cessation of leaf growth in grasses.
Technical Abstract: We examined relationships between cell-wall feruloylation, diferulate cross-linking, lignification, and apoplastic peroxidase levels on changes in the elongation rate of epidermal cells in leaf segments of slow and fast elongating genotypes of tall fescue (Festuca arundinacea Schreb.). Growth was not directly influenced by ferulic acid deposition but leaf elongation began to decelerate as 8-5-, 8-O-4-, 8-8-, and 5-5-coupled diferulic acids accumulated in cell walls. Growth rapidly slowed and stopped with the deposition of p-coumaroylated lignins into cell walls. Accretion of ferulate, diferulates and p-coumaroylated lignins continued after growth ended, into the latter stages of secondary wall formation. The concentration of 8-coupled diferulates dwarfed that of the more commonly measured 5-5-coupled diferulate, indicating that the latter dimer is a poor indicator of diferulate cross-linking in cell walls. Further work is required to clearly demonstrate that diferulate cross-linking and lignification are agents responsible for cessation of leaf growth in grasses.