Calcium Accumulation in the Leaf Spots of Tubakia dryina ‐Infected Sawtooth Oak Revealed by X‐Ray Spectroscopy and X‐Ray Microscopy

ABSTRACT Necrotic spots on sawtooth oak ( Quercus acutissima ) leaves were investigated using field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray spectroscopy (EDS) and laboratory‐based X‐ray microscopy (XRM). The spots were circular, were approximately 1 mm in diameter and had a yellow halo. Two types of leaf specimen mounting methods were employed for XRM: simple mounting and resin‐embedded mounting. FESEM revealed non‐glandular trichomes and hyphal growth on the diseased leaf samples. EDS revealed high concentrations of calcium within spots, with many distinct calcium structures, whereas such structures were rare in asymptomatic areas. Potassium levels decreased in most areas, although a uniform distribution was shown in several spots. When using the simple mounting method, XRM revealed external and internal leaf structures, including trichomes, parenchyma cells, and vascular bundles. X‐ray‐dense regions, appearing as star‐shaped or spherical druse‐shaped white objects, were found in the epidermis, mesophyll tissues, and vascular bundles. When using the resin‐embedded specimens, XRM revealed the prevalence of X‐ray‐dense regions from the trichomes to the spongy tissues. Based on the EDS analysis, the X‐ray‐dense regions and objects were derived from calcium accumulation. These results suggest that the necrotic tissues of sawtooth oak leaves may have undergone elemental relocation of calcium and potassium in response to fungal infection.