Abstract
In this study, the rate of absorption and transport of calcium (Ca) in orange fruits (Citrus sinensis cv. Fukumoto) after surface treatment with 45Ca was evaluated by supplying treatments at different dates between fruit set and mid-phase II of growth (i.e., 30, 44, 66 and 99 days after full bloom, DAFB). 45Ca absorption was always detected, but 45Ca application at the fruit set was associated with the highest rates of Ca transport into the pulp (39%) compared to the other treatments (17–19%). Scanning electron microscopy SEM) images of the fruit surface showed the occurrence of stomata along with the entire rind at all the developmental stages evaluated. However, from the beginning of stage I, stomata began to collapse and develop plugs, and this became frequent as the fruit age increased. From 44 DAFB, oil gland density increased, and Ca oxalates (CaOx) were found in the fruit flavedo and albedo. Fruit Ca (not labeled) concentration increased from fruit set (30 DAFB) to 99 DAFB, although oil gland formation and rind growth and differentiation likely hindered Ca transport to internal fruit tissues (pulp). The total Ca concentration in the pedicel was always higher than that in the fruit, with no differences between the first three treatments. The information obtained in this study may be essential for improving Ca fertilizer efficacy in citrus by spray applications.
Highlights
Calcium (Ca) has different functions in plants, such as being a structural component of the cell wall and a cytosolic messenger in cells [1]
This study aimed to evaluate the link between navel orange fruit morphology and the absorption and mobility of surface-applied Ca using 45Ca as a tracer
The success of foliar fertilization and fruit surface treatments depends on the absorption and mobility of the nutrients which are applied to the plant tissues
Summary
Calcium (Ca) has different functions in plants, such as being a structural component of the cell wall and a cytosolic messenger in cells [1]. Calcium uptake by plants from soil occurs through the roots, and its accumulation in fruit is dependent on transport through the xylem, as calcium has low phloem mobility [1,2]. Calcium influx and accumulation into the fruit have been reported to be higher during the early stages of development and decrease progressively over time [6]. This effect is likely due to the higher transpiration rates at the early stages of fruit development, which are closely related to Ca accumulation in fruit [2,4,5]
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