Calcium oxalate crystal morphology

Abstract

Plants invest considerable resources of carbon and calcium in crystal formation, indicating that it is an important basic process in growth and development. The diversity of crystal shapes, as well as their prevalence and spatial distribution, have led to several hypotheses regarding crystal function in plants. The proposed functions include roles in ion balance, in plant defense, in tissue support, in detoxification, and in light gathering and reflection [ 1. Franceschi V.R. Horner H.T. Calcium oxalate crystals in plants. Bot. Rev. 1980; 46: 361-427 Crossref Scopus (616) Google Scholar ]. The primary role of crystal formation might vary depending on the plant in question. Although calcium oxalate crystal formation has intrigued scientist for many years, knowledge of many aspects of its formation and function are unknown. Crystal formation does not appear to be a simple random precipitation event [ 2. Webb M.A. Cell-mediated crystallization of calcium oxalate in plants. Plant Cell. 1999; 11: 751-761 PubMed Google Scholar ]. Instead, crystals of specific morphologies are formed in a controlled and defined fashion. Most crystals can be classified into one of five categories based on their morphology: crystal sand, raphide, druse, styloid and prismatic [ 1. Franceschi V.R. Horner H.T. Calcium oxalate crystals in plants. Bot. Rev. 1980; 46: 361-427 Crossref Scopus (616) Google Scholar ]. Specific variations in crystal shape can occur within each classification. Such variations of the prismatic crystal morphology can be observed in the leaves of different legumes, such as Trifolium pratense, Vigna unguiculata and Vicia faba (Fig. 1). The mechanisms controlling the morphology of a crystal are unknown.