Is embolism resistance in plant xylem associated with quantity and characteristics of lignin?

The appearance of lignin during plant evolution was of defining importance in the colonization of the terrestrial environment. Among several evolutionary advantages, lignin deposition in the xylem increased mechanical support allowing plants to become tall, enabled more efficient water transport, and made the conduits strong enough to transport water under tension. Greater lignin content in the xylem may also improve resistance to embolism induced by drought. In this review we suggest, based on 91 species (54 angiosperms and 37 gymnosperms) data available for lignin content and Ψ50 (the water potential when 50% of conductivity in the xylem is lost), a limiting constraint of lignin content to embolism resistance across various groups of seed plants. For a Ψ50 reduction of approximately −0.3 MPa, plants allocate at least one percent of extra lignin to their wood. Species with low lignin content seem to be more vulnerable to embolism, whereas species with higher content show considerable variation in embolism resistance. Lignin content may play an indirect role in embolism resistance, since higher total lignin content is related to thicker cell walls. We also discuss the vulnerability to embolism regarding the different composition of lignin between gymnosperms and angiosperms and the performance of transgenic plants with modified lignin content and composition