Abstract
The presence of calcium oxalate (CaOx) crystals has been widely reported in the plant kingdom. These structures play a central role in various physiological functions, including calcium regulation, metal detoxification, and photosynthesis. However, precise knowledge about their possible roles and functions in plants is still limited. Therefore, the present work aims to study the ecotypic variability of Colobanthus quitensis, an extremophile species, concerning CaOx crystal accumulation. The CaOx crystals were studied in leaves of C. quitensis collected from different provenances within a latitudinal gradient (From Andes mountains in central Chile to Antarctica) and grown under common garden conditions. Polarized light microscopy, digital image analysis, and electron microscopy were used to characterize CaOx crystals. The presence of CaOx crystals was confirmed in the four provenances of C. quitensis, with significant differences in the accumulation among them. The Andean populations presented the highest accumulation of crystals and the Antarctic population the lowest. Electron microscopy showed that CaOx crystals in C. quitensis are classified as druses based on their morphology. The differences found could be linked to processes of ecotypic differentiation and plant adaptation to harsh environments.
Highlights
Calcium oxalate (CaOx) is an insoluble salt formed when oxalic acid ([HOOC.COOH]) combines with calcium ions (Ca2+) and precipitates
Crystal morphology is diverse, including individual needle-like styloid, large single prisms, acicular raphides occurring in bundles, crystal sands consisting of many tiny individual prisms, and druses, which are aggregates of numerous prismatic elements [8]
The morphological characteristics showed by the ecotypes agree with those obtained by Cuba-Díaz et al (2017), where the Conguillío and Arctowski (Antarctic) populations presented the most contrasting anatomical traits, and the Punta Arenas and La Parva ecotypes showed intermediate-sized structural features [17]
Summary
Calcium oxalate (CaOx) is an insoluble salt formed when oxalic acid ([HOOC.COOH]) combines with calcium ions (Ca2+) and precipitates. Among the assigned functions of CaOx crystals, the recent findings on AP, the use of CaOx as a rich source of CO2 for photosynthesis, could provide valued information for developing innovative tools regarding plant stress tolerance [10] In this context, GómezEspinoza et al (2020) studied the relationship between CO2 limiting conditions and CaOx crystal decomposition in the Antarctic plant Colobanthus quitensis [11]. In the present study, the types, morphology, and location of calcium oxalate crystals in the leaves of four C. quitensis populations (representing a latitudinal gradient from central Chile to Antarctica) were investigated in a common garden experiment. If this is the case, we would expect that populations developed at higher latitudes (lower average growth temperature and general harsher environmental conditions) would exhibit smaller and less abundant CaOx crystals than lower latitude populations in the middle of the photoperiod
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