The hierarchy of chirality

Area of Science:

• Plant Biology
• Biophysics
• Materials Science

Background:

• Long, thin vertical leaves exhibit prevalent twisting, contributing to their mechanical integrity.
• Leaf stiffness relies on turgid parenchyma cells, thickened epidermis, cuticle, vascular bundles, and fibers.
• Cellulose microfibrils in plant cell walls exhibit helical structures with specific handedness.

Purpose of the Study:

• To investigate the origin of leaf twisting at a structural and geometric level.
• To explore the relationship between cellular-level chirality and macroscopic leaf morphology.
• To elucidate the mechanism by which cellular properties contribute to leaf twist.

Main Methods:

• Analysis of cellulose microfibril orientation within plant cell walls.
• Mechanical characterization of isolated plant cells exhibiting chiral behavior.
• Development of a mathematical model to simulate collective cellular behavior.

Main Results:

• Individual plant cells with spirally arranged cellulose exhibit chiral mechanical behavior; elongation causes axial rotation.
• The mathematical model demonstrates that collective chiral cell behavior can manifest as macroscopic twist.
• Cell extension during leaf development is proposed as the mechanism driving the observed leaf twist.

Conclusions:

• Leaf twisting is a macroscopic expression of the inherent chirality of individual plant cells.
• The helical arrangement of cellulose in cell walls is fundamental to this phenomenon.
• Cellular elongation during development provides the driving force for leaf twist, enhancing mechanical stability.