Figure 9.opju from Size always matters, shape matters only for the big: potential optical effects of silica bodies in <i>Selaginella</i>

Silica bodies are commonly found in Selaginella, but their function is unclear. Lens-like appearance and location in many species above giant chloroplasts of dorsal epidermal cells suggest optical functions. Silica body morphology in three Selaginella species was studied by microscopy. Optical effects were assessed by wave-optic simulations. Large convex, approximately hemispherical (papillose) and small approximately conical (concave–convex) silica bodies were found in different species. Both types lead to concentrated spot of light high in the dorsal epidermal cell. Large convex bodies concentrate light 10–25 times in a shape-dependent manner by refraction, and small silica bodies concentrate light in a shape-insensitive, but wavelength-dependent, manner by diffraction (red light: approx. 2.3 times; blue light: approx. 1.5 times). Due to chloroplast movement, this concentrated light is above the chloroplast under high light, but within it under low light. Beyond the spot of concentration, light is dispersed into the chloroplast. Thin Selaginella leaves mean these effects may enhance light capture and minimize photodamage, but other effects such as inhibition of herbivory, mechanical support, and immune responses need to be considered. Silica bodies undoubtedly have optical effects, but their significance to the functioning of the plant requires direct studies of ecophysiological performance.硅体（Silica bodies）普遍存在于卷柏属（Selaginella）植物中，但其生理功能迄今尚未明晰。诸多物种内的硅体呈透镜状外观，且定位于背表皮细胞的巨型叶绿体上方，这一分布特征提示其可能具备光学调控功能。本研究通过显微技术对3种卷柏属植物的硅体形态进行了观测，并借助波动光学模拟（wave-optic simulations）评估了其光学效应。研究发现，不同物种分别具有大型凸面近半球形（乳突状）以及小型近锥形（凹凸形）的硅体。两类硅体均可在背表皮细胞的高位区域形成光聚集点：大型凸面硅体通过折射（refraction）作用，以形态依赖的方式将光强富集10~25倍；而小型硅体则通过衍射（diffraction）作用，以形态非依赖但波长依赖的方式聚集光线（红光约2.3倍，蓝光约1.5倍）。由于叶绿体可发生动态移动，这种聚集的光线在强光环境下位于叶绿体上方，而在弱光环境下则处于叶绿体内部。在光聚集点之外，光线会扩散至叶绿体中。卷柏属植物的叶片较为薄嫩，这使得上述光学效应既能增强光捕获效率，又可最大限度降低光损伤（photodamage）；但同时也需考虑硅体的其他潜在功能，例如抑制植食作用、提供机械支持以及参与免疫应答等。硅体无疑具备光学调控效应，但其对植物整体生理功能的实际意义，仍需通过直接的生态生理性能（ecophysiological performance）研究加以阐明。