Phenolic Components of the Plant Cell Wall

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Publisher Summary This chapter focuses on phenolic components of the plant cell wall. Phenol is the structural component common to all phenolic compounds. Both lignin and suberin are phenolic, or phenol-rich polymers, and their role in the life of the plant is well established. The chapter discusses lignin and phenolic acids in detail. There is also a description of other phenolic components in the plant cell wall such as cutin and suberin, which are lipophilic polymers. Sporopollenin is a highly resistant polymer found in the outer pollen wall of higher plants. Lignin is often present in the primary cell walls of fibers, xylem vessels, and tracheids. Lignin can be stained cytochemically by using a range of relatively specific reagents, including phloroglucinol-HCl, which responds to the cinnamaldehyde groups present in lignin. Phenolic compounds can also be detected in situ by their autofluorescence under ultraviolet light. During development, lignification often begins in the middle lamellae and primary cell walls and only later spreads into the secondary wall layers; in other tissues, however, only the secondary walls lignify. The lignin content of tissues can change quantitatively and qualitatively in response to various stimuli.