Certain Biominerals in Leaves Function as Light Scatterers

Abstract

Cystoliths are amorphous calcium carbonate bodies that form in the leaves of some plant families. Cystoliths are regularly distributed in the epidermis and protrude into the photosynthetic tissue, the mesophyll. The photosynthetic pigments generate a steep light gradient in the leaf. Under most illumination regimes the outer mesophyll is light saturated, thus the photosynthetic apparatus is kinetically unable to use the excess light for photochemistry. Here we use micro‐scale modulated fluorometry to demonstrate that light scattered by the cystoliths is distributed from the photosynthetically inefficient upper tissue to the efficient, but light deprived, lower tissue. The results prove that the presence of light scatterers reduces the steep light gradient, thus enabling the leaf to use the incoming light flux more efficiently. MicroCT and electron microscopy confirm that the spatial distribution of the minerals is compatible with their optical function. During the study we encountered large calcium oxalate druses in the same anatomical location as the cystoliths. These druses proved to have similar light scattering functions as the cystoliths. This study shows that certain minerals in the leaves of different plants distribute the light flux more evenly inside the leaf.

Precipitation of Amorphous Calcium Oxalate in Aqueous Solution

“…Employed by vertebrates, invertebrates and plants alike, 3,5,6 this strategy would appear to offer many advantages, such as access to more rapid mineralization rates and potentially greater control over the crystallization process. While it is recognized that some crystalline iron oxide biominerals, for example magnetite in magnetotactic bacteria and chiton teeth, 7 can form via the poorly-ordered phase ferrihydrite, there is as yet insufficient data available to determine whether this mechanism is common across the large number of known crystalline biominerals.…”

Best of Both Worlds: Simultaneous High-Light and Shade-Tolerance Adaptations within Individual Leaves of the Living Stone Lithops aucampiae

“…When viewed under cross-polarised light, the conical below-ground epidermal cells showed internal microcrystalline deposits around or within cell walls with light inference properties corresponding to that of calcium oxalate [14] (Fig. 1(b) iii ), previously observed in foliar tissues of other plant species [15], [16]. No reflectance of cross-polarised light was observed in any of the other sections (Fig.…”

Comparative leaf and stem anatomy in selected species of Ruellieae (Acanthaceae) representative of all major lineages

“…The two different orientations of cystoliths in leaves, which appears to be governed by their proximity to the midrib (herein documented as well as in Kuo-Huang & Yen 1996), may signify two different functions of these structures in the leaf. For example, one hypothesis is that cystoliths serve a structural function proximal to midribs whereas elsewhere in the leaf blade, cystoliths serve to scatter light and reduce photoinhibition, shifting light from photonsaturated upper mesophyll cells to light-limited lower mesophyll cells (Gal et al 2012). This leaves open the question as to their original function or adaptive value, if any, during their early appearance(s) evolutionarily within Acanthaceae.…”