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Throughout leaf development, cell expansion is dynamic and driven by the balance between local cell wall mechanical properties and the intracellular turgor pressure that overcomes the stiffness of the cell wall leading to plastic deformation. The epidermal pavement cells in most leaves begin development as small, polygonally shaped cells, but in mature leaves epidermal pavement cells are often shaped as highly lobed puzzle pieces. However, the developmental and biomechanical trajectories between these two end points have not before been fully characterized. Here we characterized how epidermal pavement cell size and shape, cell wall thickness, and hydraulic traits change during leaf expansion in the tropical understory fern Microsorum grossum (Polypodiaceae). As fronds expanded by approximately two orders of magnitude in size, epidermal pavement cells became increasingly lobed as cell walls thickened. Furthermore, the timing of these developmental changes varied across the lamina, start first near the frond base and midrib, followed by more apical and lateral regions. During expansion, fronds also underwent substantial physiological changes: as cells expanded and cell walls thickened, intracellular turgor pressure and the bulk cell wall modulus of elasticity both increased while the water potential at turgor loss and the minimum epidermal conductance to water vapor both decreased. These results highlight the dynamic coordination between anatomical and physiological traits throughout leaf development, provide valuable data for biophysical modeling of leaf development, and highlight the vulnerability of developing leaves to drought conditions.
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Convergent evolution of cell size enables adaptation to the mangrove habitat
Mangroves have evolved at least 27 times across ~20 plant families to survive coastal. To environments characterized by high salinity, inundation, intense light, and strong winds survive these extreme conditions, mangroves exhibit a variety of physiological strategies to tolerate the low osmotic potentials associated with saltwater inundation. Because low osmotic potentials are counterbalanced by high turgor pressure, saltwater exposure exerts mechanical demands on cells. Analyzing 34 mangrove species and 33 closely related inland taxa from 17 plant families, we show that compared to their inland relatives, mangroves have unusually small leaf epidermal pavement cells and thicker cell walls, which together confer greater mechanical strength and tolerance to low osmotic potentials. However, mangroves do not exhibit smaller, more numerous stomata that enable higher photosynthetic rates , suggesting selection on biomechanical integrity rather than on gas exchange capacity. Notably, mangroves break the allometric scaling between the sizes of epidermal pavement cells and stomata typically seen in land plants, highlighting that strong selection in saline habitats can override genome size–mediated scaling rules. Phylogenetic comparative analyses revealed repeated convergent evolution of cell traits across independent transitions from inland to coastal habitats. These anatomical changes constitute a simple but effective adaptation to salt stress. Our findings underscore the role of biomechanics in driving convergent evolution of cell traits and suggest that manipulating cell size and wall properties could be a promising strategy to engineering salt-tolerant plants.
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- PAR ID:
- 10647522
- Publisher / Repository:
- Cell Press
- Date Published:
- Journal Name:
- Current biology
- ISSN:
- 0960-9822
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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