Calcium oxalate crystals, the plant "gemstones": Insights into their synthesis and physiological implications in plants.

Abstract

From simple algal forms to the most advanced angiosperms, calcium oxalate (CaOx) crystals 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 synthesis, and sometimes environmental stresses. Certainly, the occurrence of CaOx crystals 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/oxalate detoxification, light reflectance and photosynthesis, and protection against grazing and herbivory, besides other characteristics, are gaining much interest. So, 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 crystals in plants (and soil). Overall, insights and the conceptual future directions present them as potential biominerals to address future climate-driven issues.