Effect of foliar Ca spraying on calcium dynamics, fractions and subcelluar distribution of pulp cells of Feicheng peach

【Objectives】 Feicheng peach has been always suffered from problems such as browning and poor storability. Calcium fertilization is an effective measure to deal with these problems. Understanding the absorption and distribution of calcium in cells will provide a theoretical basis for calcium fertilization.【Methods】 A field experiment was conducted with 11 year-old Feicheng peach trees as materials in Feicheng City, Shandong Province. 0.5% amino acid-Ca and 0.5% Ca(NO3)2 were used as Ca fertilizers, and foliar spraying was carried out every 30 days since one month after the florescence, and water was sprayed in the same way in control. The skin, flesh, stone and seed samples were collected every 30 days since 37 days after florescence. The contents of different calcium fractions were measured. The Ca subcelluar distribution in pulp cells was observed using electrical microscope. 【Results】 The highest calcium content was in young fruit stage. The total calcium contents, water soluble calcium contents and pectate calcium contents showed downward trends with the maturity of the fruits. Spraying calcium increased the total calcium contents in the skin, flesh, stone and seeds, with the most significant increase in flesh. At the fruit mature period, the total Ca contents of flesh treated with amino acid-Ca and Ca (NO3)2 were increased by 68% and 77%. Observed with the electron microscope, the Ca treated pulp cells showed uniform calcium distribution on the cell wall, cell membrane and vacuole membrane; calcium was accumulated in the vacuole. The pulp cells without calcium treatment showed decreases of the calcium contents in cell wall, and calcium uniform distribution in cell membrane and vacuole membrane. The browning pulp cells showed the rare and uneven calcium distribution. 【Conclusions】 The total calcium contents decreased rapidly with the growth of Feicheng peach. Spraying calcium increased the contents of activated calcium and calcium distribution in the cell walls, so it was beneficial to remit the decrease of calcium content in the fruit development. Spraying different forms of calcium increased insoluble pectin contents of flesh and increased the firmness of fruits.