Distribution of Calcium in Fruit Tissues of Loquat

Fruits are a good source of various minerals for humans. Calcium in fruits is important for normal development and quality maintenance. The present study examined calcium distribution in different fruit tissues of 'Zhaozhong No. 6' loquat (Eriobtorya japonica Lindl.). Calcium concentration in young fruit was high but declined throughout fruit development, while in the pedicel calcium concentration was relatively constant and became far higher than in fruit flesh and seed as fruit matured. Calcium mapping in the flesh using X-ray microanalyzer revealed that a larger amount of Ca was distributed in the outer portion or exocarp, where a large number of calcium-rich particles were found in young fruit. These calcium-rich particles disappeared as fruit grew and matured. Within the pedicel, calcium was more abundant in the phloem and pith than in the cortex and xylem. There were a lot of calcium oxalate crystals, either in styloids or druses, in the phloem and pith cells neighboring the xylem and fiber clusters, where Ca level was the lowest. There was a good positive correlation between Ca content in the pedicel and that in the flesh. It was concluded that Ca is likely transported to fruit through the phloem tissues and that the formation of calcium oxalate in the pedicel may not interfere with calcium transport to fruit.