School of Plant Biology, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
Ann Bot. 2012 Apr;109(5):887-96. doi: 10.1093/aob/mcs004. Epub 2012 Jan 31.
Formation of calcium oxalate crystals is common in the plant kingdom, but biogenic formation of calcium sulfate crystals in plants is rare. We investigated the morphologies and elemental compositions of crystals found in phyllodes and branchlets of Acacia robeorum, a desert shrub of north-western Australia.
Morphologies of crystals in phyllodes and branchlets of A. robeorum were studied using scanning electron microscopy (SEM), and elemental compositions of the crystals were identified by energy-dispersive X-ray spectroscopy. Distributional patterns of the crystals were studied using optical microscopy together with SEM.
According to the elemental compositions, the crystals were classified into three groups: (1) calcium oxalate; (2) calcium sulfate, which is a possible mixture of calcium sulfate and calcium oxalate with calcium sulfate being the major component; and (3) calcium sulfate · magnesium oxalate, presumably mixtures of calcium sulfate, calcium oxalate, magnesium oxalate and silica. The crystals were of various morphologies, including prisms, raphides, styloids, druses, crystal sand, spheres and clusters. Both calcium oxalate and calcium sulfate crystals were observed in almost all tissues, including mesophyll, parenchyma, sclerenchyma (fibre cells), pith, pith ray and cortex; calcium sulfate · magnesium oxalate crystals were only found in mesophyll and parenchyma cells in phyllodes.
The formation of most crystals was biologically induced, as confirmed by studying the crystals formed in the phyllodes from seedlings grown in a glasshouse. The crystals may have functions in removing excess calcium, magnesium and sulfur, protecting the plants against herbivory, and detoxifying aluminium and heavy metals.
草酸钙晶体的形成在植物界很常见，但生物形成的硫酸钙晶体在植物中则较为罕见。我们研究了澳大利亚西北部沙漠灌木金合欢树的叶状柄和小枝中发现的晶体的形态和元素组成。
使用扫描电子显微镜（SEM）研究了金合欢树叶状柄和小枝中晶体的形态，并用能谱仪（EDS）鉴定了晶体的元素组成。使用光学显微镜和 SEM 研究了晶体的分布模式。
根据元素组成，晶体可分为三组：（1）草酸钙；（2）硫酸钙，可能是硫酸钙和草酸钙的混合物，其中硫酸钙为主要成分；（3）硫酸钙·草酸镁，可能是硫酸钙、草酸钙、草酸镁和硅的混合物。晶体具有各种形态，包括棱柱体、针状体、棒状体、晶簇、晶砂、球体和聚集体。草酸钙和硫酸钙晶体几乎存在于所有组织中，包括叶肉、薄壁组织、厚壁组织（纤维细胞）、髓、髓射线和皮层；仅在叶状柄的叶肉和薄壁组织细胞中发现了硫酸钙·草酸镁晶体。
通过研究在温室中生长的幼苗的叶状柄形成的晶体，证实了大多数晶体是生物诱导形成的。这些晶体可能具有去除多余钙、镁和硫的功能，保护植物免受食草动物侵害，并解毒铝和重金属。
