Light makes plants stronger but also holds them back

The research team, led by Professor Kouichi Soga of the Graduate School of Science, focused on young pea stems. Using a specialized technique, they measured how strongly the epidermal (the outermost layer) is attached to the inner tissues. Their results showed a clear difference depending on light exposure.

Plants grown in light had much stronger adhesion between these layers than those grown in darkness.

"Compared with plants grown in the dark, the epidermal and inner tissues of plants grown in the light are more tightly bound together," Professor Soga said. "This phenomenon has never been reported before, making it a particularly interesting finding."

Key Compound p-Coumaric Acid Identified

To understand what was causing this stronger connection, the researchers examined the plant cells using a fluorescence microscope. They observed that stems exposed to light emitted signals linked to higher levels of a compound called p-coumaric acid.

This phenolic acid is known to help reinforce plant cell walls. Its presence suggests that light exposure increases the production of this compound, which in turn strengthens the structural bonds within the plant.

"This provided strong evidence that the accumulation of p-coumaric acid was a key factor in strengthening the adhesion between the epidermal and the inner tissues," Yuma Shimizu, a graduate student and first author of the study, explained.

Stronger Structure Can Limit Plant Growth

The findings reveal an interesting trade-off. While stronger adhesion makes the plant more structurally stable, it also reduces its ability to grow.

When the outer and inner tissues are tightly bound, the inner tissues cannot expand as easily. This limits overall stem growth, meaning that light not only supports plant development but can also slow it under certain conditions.

Implications for Agriculture and Crop Resilience

The researchers believe this mechanism could be part of a broader pattern in plant biology. By continuing to study how adhesion changes as plants respond to different conditions, they hope to determine whether this is a universal way plants regulate growth.

"By measuring the adhesion between the epidermal and the inner tissues as stem growth changes in response to various factors, we expect to determine whether growth regulation mediated by changes in adhesion is a universal mechanism," Professor Soga concluded. "These findings could be highly significant for plant cultivation. If we can control adhesion, it may be possible to breed plants with improved tolerance to environmental stress."

The findings were published in Physiologia Plantarum.