The Investigation of Silicon Localization and Accumulation in Citrus

Several studies have demonstrated Si absorption in monocotyledon and dicotyledon species. Regarding Si accumulation, studies in monocotyledons have identified Si deposition around the cell wall, cuticle layer bulliform cells, silica cells and endodermal cells. In previous studies with different citrus species there were evidence of Si accumulation, however no information on Si deposition can be found. Therefore, in this study, Si was applied (0 and 1000 mg L^-1) to the roots of two citrus species, 'Delta' Valencia (Citrus sinensis) and 'Nules' Clementine (Citrus reticulata). Si accumulation were investigated in new, and old leaves and roots. Si deposition was investigated through scanning electron microscopy using energy dispersive analysis X-ray, environmental scanning electron microscopy and light microscopy. Si accumulation was significantly higher in Si treated leaves comparatively to the control in both young and mature leaves. Meanwhile, Si accumulation increased with leaf age. Additionally, Si accumulation was significantly higher in roots than in leaves. With respect to Si deposition, granules were identified in the epidermal cells through SEM and ESEM studies. The light microscopy identified the presence of Si granules in the surface and around the outer cell surface forming the cuticle-silica double layer of the lower epidermis in Si treated plants. Silica deposit were not found on the abaxial leaf surface. The findings suggest a passive uptake in citrus species.