Decomposition of Calcium Oxalate Crystals in Colobanthus quitensis under CO2 Limiting Conditions

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.

Ecophysiology of Antarctic Vascular Plants: An Update on the Extreme Environment Resistance Mechanisms and Their Importance in Facing Climate Change

Antarctic flowering plants have become enigmatic because of their unique capability to colonize Antarctica. It has been shown that there is not a single trait that makes Colobanthus quitensis and Deschampsia antarctica so special, but rather a set of morphophysiological traits that coordinately confer resistance to one of the harshest environments on the Earth. However, both their capacity to inhabit Antarctica and their uniqueness remain not fully explained from a biological point of view. These aspects have become more relevant due to the climatic changes already impacting Antarctica. This review aims to compile and update the recent advances in the ecophysiology of Antarctic vascular plants, deepen understanding of the mechanisms behind their notable resistance to abiotic stresses, and contribute to understanding their potential responses to environmental changes. The uniqueness of Antarctic plants has prompted research that emphasizes the role of leaf anatomical traits and cell wall properties in controlling water loss and CO2 exchange, the role of Rubisco kinetics traits in facilitating efficient carbon assimilation, and the relevance of metabolomic pathways in elucidating key processes such as gas exchange, nutrient uptake, and photoprotection. Climate change is anticipated to have significant and contrasting effects on the morphophysiological processes of Antarctic species. However, more studies in different locations outside Antarctica and using the latitudinal gradient as a natural laboratory to predict the effects of climate change are needed. Finally, we raise several questions that should be addressed, both to unravel the uniqueness of Antarctic vascular species and to understand their potential responses to climate change.

Calcium Oxalate Crystals, the Plant 'Gemstones': Insights into Their Synthesis and Physiological Implications in Plants

From simple algal forms to the most advanced angiosperms, calcium oxalate (CaOx) crystals (CRs) occur in the majority of taxonomic groups of photosynthetic organisms. Various studies have demonstrated that this biomineralization is not a simple or random event but a genetically regulated coordination between calcium uptake, oxalate (OX) synthesis and, sometimes, environmental stresses. Certainly, the occurrence of CaOx CRs is old; however, questions related to their genesis, biosynthesis, significance and genetics exhibit robust evolution. Moreover, their speculated roles in bulk calcium regulation, heavy metal/OX detoxification, light reflectance and photosynthesis, and protection against grazing and herbivory, besides other characteristics, are gaining much interest. Thus, it is imperative to understand their synthesis and regulation in relation to the ascribed key functions to reconstruct future perspectives in harnessing their potential to achieve nutritious and pest-resistant crops amid anticipated global climatic perturbations. This review critically addresses the basic and evolving concepts of the origin (and recycling), synthesis, significance, regulation and fate vis-à-vis various functional aspects of CaOx CRs in plants (and soil). Overall, insights and conceptual future directions present them as potential biominerals to address future climate-driven issues.

Crystal idioblasts are involved in the anther dehiscence of Nicotiana tabacum

In Nicotiana tabacum, the degeneration of connective tissue and stomium tissue (the stomium and circular cell cluster [CCC]) is essential for anther dehiscence. Both connective cells and CCC cells are crystal idioblasts, and these cells will undergo degeneration after accumulating calcium oxalate (CaOx) crystals. However, detailed data concerning this process are minimal. Therefore, this study used cellular biological and physiological methods to illustrate this relationship. Results demonstrated that tobacco anther dehiscence is a series of timed programmed cell death (PCD) processes that include the CCC, connective tissue, and stomium. The degenerating crystal idioblasts of the tobacco anther were found to possess two hallmark characteristics that distinguished them from normal PCD cells, namely dynamic changes in CaOx crystals and the appearance of numerous peroxisomes. The accumulation of CaOx and the production of H₂ O₂ occurred simultaneously or successively before PCD. The peak H₂ O₂ content was found to appear after the insoluble oxalate. Further, CeCl₃ cytochemistry staining was used to detect subcellular H₂ O₂ , and the precipitate of H₂ O₂ was primarily present in peroxisomes and around CaOx crystals. These results show that anther dehiscence in N. tabacum is a PCD process in which crystal idioblasts play a vital role in CaOx degradation and H₂ O₂ production.

A comparative study on the leaf anatomical structure of Camellia oleifera in a low-hot valley area in Guizhou Province, China

The leaf serves as an important assimilation organ of plants, and the anatomical structure of leaves can reflect the adaptability of the plant to the environment to a certain extent. The current study aimed to cultivate superior local cultivars, and 35 healthy individual plants were selected from the Camellia oleifera germplasm resource nursery for a comparative study of the leaf structure. In July 2019, the leaves were collected from 35 selected healthy C. oleifera plants, and the leaf structure was observed by using the paraffin section method. Healthy individual plants were screened using variance analysis, correlation analysis and cluster analysis. The representative indices were selected according to the cluster membership, correlation indices and coefficient of variation (C/V) for a comprehensive evaluation of drought resistance via the membership function. There were extremely significant differences in 11 indices of leaf structure for these 35 healthy plants. C18 had the greatest leaf thickness, C7 the largest spongy tissue, and C38 the largest ratio of palisade tissue thickness to spongy tissue thickness (P/S). The clustering results of the healthy individual plants differed significantly. The membership function showed that the drought resistance of 35 C. oleifera plants was divided into five categories. C18 had very strong drought resistance, and C3, C7 and C40 had strong drought resistance. There were significant differences in terms of the upper epidermis, P/S ratio and spongy tissue among the C. oleifera plants. C18, C3, C7 and C40 exhibited satisfactory drought resistance. Although C39 and C26 had moderate drought resistance, their P/S ratios were high, which might be used to cultivate high-yield and drought-resistant C. oleifera varieties. The leaf P/S ratio of C. oleifera from low-hot valley areas was high. Among various leaf structures, spongy tissue, upper epidermis, P/S ratio and cuticle constitute the drought resistance evaluation indices for C. oleifera grown in low-hot valley areas.

Calcium Oxalate Crystals in Leaves of the Extremophile Plant Colobanthus quitensis (Kunth) Bartl. (Caryophyllaceae)

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.