In Situ Accumulation of CaOx Crystals in C. quitensis Leaves and Its Relationship with Anatomy and Gas Exchange.

The accumulation of crystal calcium oxalate (CaOx) in plants is linked to a type of stress-induced photosynthesis termed 'alarm photosynthesis', serving as a carbon reservoir when carbon dioxide (CO2) exchange is constrained. Colobanthus quitensis is an extremophyte found from southern Mexico to Antarctica, which thrives in high-altitude Andean regions. Growing under common garden conditions, C. quitensis from different latitudinal provenances display significant variations in CaOx crystal accumulation. This raises the following questions: are these differences maintained under natural conditions? And is the CaOx accumulation related to mesophyll conductance (gm) and net photosynthesis (AN) performed in situ? It is hypothesized that in provenances with lower gm, C. quitensis will exhibit an increase in the use of CaOx crystals, resulting in reduced crystal leaf abundance. Plants from Central Chile (33°), Patagonia (51°), and Antarctica (62°) were measured in situ and sampled to determine gas exchange and CaOx crystal accumulation, respectively. Both AN and gm decrease towards higher latitudes, correlating with increases in leaf mass area and leaf density. The crystal accumulation decreases at higher latitudes, correlating positively with AN and gm. Thus, in provenances where environmental conditions induce more xeric traits, the CO2 availability for photosynthesis decreases, making the activation of alarm photosynthesis feasible as an internal source of CO2.

Morphological and micromechanical characterization of calcium oxalate (CaOx) crystals embedded in the pecan nutshell (Carya illinoinensis).

The morphology and micromechanical properties of the mineral crystals embedded in the pecan nutshell (Carya illinoinensis) were characterized. Qualitative and quantitative morphological analyses carried out revealed that the crystals were comprised of calcium oxalate (CaOx) and have a wide range of sizes, with prismatic shapes, distributed heterogeneously in the sclerenchyma tissue. From indentation tests, it was found that CaOx crystals are stiffer structures compared to stone cells (sclerenchyma tissue), showing hardness and elastic modulus values of 0.53 ±â€¯0.19 GPa and 9.4 ±â€¯1.80 GPa, respectively. Additionally, the values of fracture toughness (0.08 ±â€¯0.02 MPa m0.5) and the brittleness index (9336 m-0.5) revealed that these types of structures are extremely brittle. The results obtained suggest that the main function of the CaOx crystals is to provide structural support to tissue. The presented methodology demonstrates the potential of the instrumented indentation technique (IIT) for in situ micromechanical characterization of mineral crystals located in plant tissues.