Calcium oxalate biomineralization in plants

Abstract

Calium oxalate (CaOx) biomineralization with diverse and species-specific morphologies and structures formed in specialized cells (idioblast) is a basic and important process in many plant families. During their formation there exist the synergetic interactions between cell growth/expansion and crystal nucleation/growth, indicating that the mineralization process is precisely controlled by biomacromolecules through the exquisite bio-regulation mechanisms rather than a simple chemical precipitation reaction. The mineralized phases and the final mature products formed inside cells are shaped and thermodynamically stabilized by various biomacromolecules expressed and synthesized in corresponding bio-pathways. CaOx crystals in plants fulfill a variety of crucial functions, including the high-capacity calcium regulation and self-protection of plants against herbivory by large animals as well as insects, this may reflect an evolutionary signature under various environmental stresses. In this review, the possible biochemical events in relation to CaOx crystal formations in vivo will be discussed, especially for the oxalic acid biosynthetic pathways, the uptake and accumulation of calcium ions and modulation of crystallization as well. In addition, recent progress in dynamics of CaOx crystallization in vitro at the near-molecular level provides new insights into the molecular mechanisms of formation and function of CaOx crystals in plants.