3.2 Leaf anatomy of Capparis odoratissima: cuticles, peltate hairs and idioblasts.
Leaf cross-sections revealed that the idioblasts are thick-walled columnar structures that connect the adaxial and the abaxial surfaces (Figure 2a, drawn by Metcalfe & Chalk, 1950). Idioblasts did not stain for lipids, but auramine O staining revealed a thick cuticle layer on the adaxial surfaces of the leaves (Figure 2b), which was thinner in the concave depressions on top of the idioblasts. In contrast, the thick columnar walls of the idioblasts stained intensely with calcofluor white (Figure 2c) indicating the presence of cellulose in the thick walls, while staining with phloroglucinol indicated partial lignification. The abaxial surface of the leaf showed a thinner but rugose cuticle under the peltate hairs (Figure 2d). At the anchoring areas of the peltate hairs, the abaxial epidermis accumulated thick lipidic deposits (Figure 2e).
Idioblasts exhibited a bipolar pattern from the adaxial to the abaxial side of the leaf (Figure 3a). A thin projection that protruded apoplastically between the cells of the upper epidermis connected with the surface, and was sustained underneath with four-to-five filiform anchors attached to the base of the epidermal cells (Figure 3b). In the area of the palisade parenchyma, the idioblasts had a columnar shape, with a thick wall, narrow lumen, and crenations that connected the lumen with the palisade parenchyma (Figure 3c). In the spongy mesophyll, the irregular shape of idioblasts was characterized by numerous protuberances and crenations that connected the lumen of the idioblasts with adjacent mesophyll cells (Figure 3d). Closer to the abaxial side of the leaf, the idioblasts became thinner, as well as anastomosed and converged toward the base of the peltate hairs, maintaining narrow channels that connected the lumen of the idioblast with the lumen of the peltate hair (Figure 3e). On average, four idioblasts were connected to each peltate hair (Figure 4), whereas the frequency of abaxial stomata under the peltate hairs was significantly lower than that of idioblasts.