Self‐repair in cacti branches: Comparative analyses of their morphology, anatomy, and biomechanics

Abstract

Damage‐repair is particularly important for the maintenance of the water‐storing abilities of succulent plants such as cacti. Comparative morphological, anatomical, and biomechanical analyses of self‐repair were performed on artificially wounded branches of Opuntia ficus‐indica and Cylindropuntia bigelovii. Macroscopic observations, contrast staining, and lignin‐proof staining were used to investigate morphological and anatomical responses after wounding at various time intervals. Two‐point bending tests were repeatedly performed on the same branches under unwounded, freshly wounded, and healed conditions by using customized 3D‐printed clamping jaws. Morphologically, both species showed a rolling‐in of the wound edges, but no mucilage discharge. Anatomically, ligno‐suberized peridermal layers developed that covered the wound region, and new parenchyma cells formed, especially in O. ficus‐indica. In all samples, the wounding effect directly after damage caused a decrease between 18% and 37% in all the tested mechanical parameters, whereas a positive healing effect after 21 days was only found for C. bigelovii. Based on our data, we hypothesize a high selection pressure on the restoration of structural integrity in the wound area, with a focus on the development of efficient water‐retaining mechanisms, whereas the concept of “sufficient is good enough” seems to apply for the restoration of the mechanical properties.