9 - Early land plant adaptations to terrestrial stress: A focus on phenolics

Abstract

This chapter maps the stress-related physiological traits onto a robust phylogeny for modern charophycean algae and bryophytes. Trait mapping suggests that early phenolics could have been preadaptive to the development of stable plant–microbe relationships. As in modern plants, phenolic compounds may have controlled microbial behavior, allowing microbes to live in close proximity to algae and early land plants without becoming pathogenic. The chapter also compares the aspects of phenolic chemistry among charophyceans, bryophytes, and pteridophytes and estimates the extent to which nonvascular plants could have contributed to carbon sequestration prior to the origin of vascular plants. Thioacidolysis was used as an assay for lignin-specific β-O-4 phenolic linkages in representative green algae and early-divergent land plants. Selected green algae and bryophytes were surveyed for the presence of resistant biomass and the percentages of resistant cell wall biomass were quantitatively determined. The amount of resistant organic carbon that might have been generated by early non-vascular land plants was also estimated. Adaptive utility for high levels of wall phenolics might include (1) resistance to attack by pathogenic bacteria, protists and fungi, (2) increased stability of cell walls, contributing to the ability to achieve increased height, (3) UV-damage resistance, and (4) desiccation resistance.