Plant pipe cell reinforced with lignin
Plant pipe cell reinforced with lignin is highly resistant to negative pressure in contrast to the other flattened cells around. Photo using Scanning Electron Microscopy (SEM): Cheng Choo Lee

Lignin, the second most abundant biopolymer on Earth, represents about 30 percent of the total carbon on the planet. It allows plants to conduct water and stand upright; without lignin, plants cannot grow nor survive.

“Plants are made of many different cells, some of them are reinforced with lignin and assemble to each other to form a pipe that conducts water, like a straw to drink your cocktail”, explains Delphine Ménard, Head of the cell cultures platform at Stockholm University Department of Ecology, Environment and Plant Sciences (DEEP), “lignin is so strong that the pipe cells can resist vacuum while other cells are flattened”.

Existence of a lignin “chemical code”

For long, scientists did not consider that lignin had a “code” like in DNA or proteins. Researchers led by DEEP in collaboration with Stockholm University Department of Materials and Environment Chemistry (MMK) and Tokyo University of Agriculture and Technology (TUAT) have now challenged this old paradigm by demonstrating the existence of a lignin “chemical code”. They showed that each cell uses this “chemical code” to adjust their lignin to function optimally and resist stresses. These results are published in the journal The Plant Cell and could be used in both agriculture and forestry to tackle future climate challenges.

“It takes only one simple chemical change, just one hydrogen atom apart from alcohol to aldehyde to make plants highly resilient to drought in conditions where alcohol-rich plants would all die”, explain Edouard Pesquet, Associated Professor in molecular plant physiology and senior author of the study.

Interestingly, Professor Shinya Kajita from TUAT showed that such large increases of lignin aldehydes can occur naturally in the wild. In the Japanese silk industry for example, mulberry with the highest lignin aldehyde levels have long been used and loved by silk caterpillar.

Possibilities to improve crops and trees

Edouard Pesquet
Associate Professor Edouard Pesquet observing samples using classical imaging. Photo: Sepehr Bardi

“These results revise our understanding of lignin and plant water conduction, but also open great possibilities to use the lignin code to improve crops and trees to face water availability problems. The modification of lignin chemistry at the single cell level is ultimately the mechanism enabling plants to grow, hydrate and resist climate change stresses”, says Edouard Pesquet.

The study “Plant biomechanics and resilience to environmental changes are controlled by specific lignin chemistries in each vascular cell type and morphotype” by Ménard, Blaschek et al. is published in the journal The Plant Cell in September 2022.

This article was originally published on Stockholm University's website.