Anatomical mechanisms underlying desiccation-induced nastic movements in Doryopteris ferns (Pteridaceae).

Several ferns of the subfamily Cheilanthoideae exhibit reversible leaf curling under water deficit. However, the anatomical mechanisms underlying this behavior remain poorly understood. To address this knowledge gap, we hypothesize that blade folding during dehydration is driven by structural features that allow reversible tissue deformation. The tissues could generate differential tension across the lamina through asymmetric contractions. Their hygroscopic nature may promote passive curling during dehydration and unfolding during rehydration. To test this hypothesis, we analyzed fronds of five species of Doryopteris (D. arifolia, D. collina, D. concolor, D. lorentzii and D. pentagona) under normal hydration and induced water stress. Material was collected and fixed in formalin–acetic acid–alcohol, and examined using light microscopy and scanning electron microscopy. The anatomy of D. arifolia and D. collina is described for the first time, and structural changes between both physiological states are reported for all species studied. Under water stress, epidermal cells contracted as a consequence of dehydration, resulting in small folds on the outer walls. The mesophyll reduced its thickness and reorganized parenchyma cells, increasing intercellular spaces in the central region while compacting the margins. Vascular bundles exhibited contraction of the phloem and associated parenchyma. Macrosclereids and lignified cells showed modifications in lumen shape and size, whereas petioles, like bundles, displayed collapsed phloem. These results indicate that lamina curling in Doryopteris results from the combined response of epidermis, mesophyll, and supporting tissues to water loss. The reversible changes of tissues reduce mechanical damage and allow lamina reexpansion after rehydration, providing flexibility against environmental changes in humidity.