Wound reactions in stems of Leonurus cardiaca: a morphological, anatomical, and biomechanical study

During biological evolution, plants evolved various types of wound reactions. This study focuses on the self-healing of plant fibers in the model plant Leonurus cardiaca L. In one of the square-shaped internodes of each plant, all four prominent strands of the collenchyma were damaged by a razor blade with a central incision in a longitudinal direction. After 20 to 24 days, the morphology, anatomy, and biomechanics of the healed internodes were compared with undamaged controls. Stem height increased highly significantly in the healed and control plants, although the healed internodes were significantly shorter than the respective control internodes. Light microscopy examination of the wounded region revealed permanent gaping of the wound and the formation of a distinct boundary layer. Four-point-bending tests showed a significantly lower flexural rigidity (self-healing efficiency = 44%) and a highly significantly lower bending elastic modulus (self-healing efficiency = 66%) for the healed internodes compared with the controls, although the axial second moments of area did not differ significantly (self-healing efficiency = 82%). After a healing period of three weeks, recovery of the morphological–anatomical characteristics and mechanical properties of the healed internodes was incomplete compared with the undamaged control samples. Nevertheless, the self-healing efficiency seemed to be sufficient to ensure the integrity of the stem during the entire growth period.