Abstract
Lignin is the second most abundant natural polymer on Earth and is a major cell wall component in vascular plants. Lignin biosynthesis has three stages: biosynthesis, transport, and polymerization of its precursors. However, there is limited knowledge on lignin precursor transport, especially in monocots. In the present study, we aimed to elucidate the transport mode of lignin monomers in the lignifying tissues of bamboo (Phyllostachys pubescens). The growth manners and lignification processes of bamboo shoots were elucidated, which enabled us to obtain the lignifying tissues reproducibly. Microsomal membrane fractions were prepared from tissues undergoing vigorous lignification to analyze the transport activities of lignin precursors in order to show the ATP-dependent transport of coniferin and p-glucocoumaryl alcohol. The transport activities for both precursors depend on vacuolar type H+-ATPase and a H+ gradient across the membrane, suggesting that the electrochemical potential is the driving force of the transport of both substrates. These findings are similar to the transport properties of these lignin precursors in the differentiating xylem of poplar and Japanese cypress. Our findings suggest that transport of coniferin and p-glucocoumaryl alcohol is mediated by secondary active transporters energized partly by the vacuolar type H+-ATPase, which is common in lignifying tissues. The loading of these lignin precursors into endomembrane compartments may contribute to lignification in vascular plants.
Highlights
IntroductionTo study the transport of lignin precursors, Miao and Liu conducted transport experiments using microsomal membrane fractions derived from rosette leaves of Arabidopsis thaliana [4]
Lignin is a major cell wall component of vascular plants and the second most abundant natural polymer on Earth
One ATP-binding cassette (ABC) transporter in A. thaliana, AtABCG29, was reported to be a transporter of p-coumaryl alcohol, the monolignol of the H-unit lignin [5], the amount of H-unit lignin is very limited in most vascular plants
Summary
To study the transport of lignin precursors, Miao and Liu conducted transport experiments using microsomal membrane fractions derived from rosette leaves of Arabidopsis thaliana [4]. The rosette leaves of herbal plants like Arabidopsis have very little lignified tissue, and the parenchyma of the leaves may be involved in these transport activities. One ABC transporter in A. thaliana, AtABCG29, was reported to be a transporter of p-coumaryl alcohol, the monolignol of the H-unit lignin [5], the amount of H-unit lignin is very limited in most vascular plants. Studies on A. thaliana have attempted to identify the ABC transporters of lignin precursors [6,7,8]; the transporters of lignin precursors of the G and S units have not been elucidated
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