Among the higher plants that accumulate crystalline calcium oxalate, many taxa characteristically produce raphides, or needle‐shaped crystals. Substantial evidence has accumulated indicating that raphides function in plant defenses against herbivory and that their acicular shape is a critical component in proposed mechanisms for these defenses. Previous observations have shown that raphides in members of the Vitaceae are twinned crystals. In this study, the fine structure of raphides in Vitis was examined in order to determine the nature of twinning. Rotation of isolated raphides under cross‐polarized light revealed extinction patterns that indicated that raphides are twinned along their length. In cross sections of raphides, the twin plane extends across the raphides, parallel to their surfaces. The dissolution patterns observed in etched crystals indicate that the type of twinning is rotational. Parallels in other biomineralization systems indicate that the rotational nature of the twinning may increase mechanical strength. In addition, because twinning may affect crystal growth or enhance stability and persistence of crystals, it could be an important factor in allowing plant cells to produce the raphide morphology.

中文翻译：

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葡萄 (Vitis) 中草酸钙孪晶：对晶体稳定性和功能的影响

在积累结晶草酸钙的高等植物中，许多分类群的特征是产生针状晶体或针状晶体。已经积累的大量证据表明，raphides 在植物防御食草动物中发挥作用，并且它们的针状形状是这些防御机制的关键组成部分。先前的观察表明，葡萄科植物中的 raphides 是孪晶晶体。在这项研究中，检查了葡萄中针刺的精细结构，以确定孪生的性质。在交叉偏振光下，孤立的 raphides 的旋转揭示了消光模式，表明 raphides 沿着它们的长度是孪生的。在针晶的横截面中，孪晶平面延伸穿过针晶，平行于它们的表面。在蚀刻晶体中观察到的溶解模式表明孪晶类型是旋转的。其他生物矿化系统的相似之处表明孪晶的旋转性质可能会增加机械强度。此外，由于孪晶可能会影响晶体生长或增强晶体的稳定性和持久性，因此它可能是允许植物细胞产生针晶形态的重要因素。