CaMov - characterization of calcium foliar uptake, and translocation to fruits: searching for mobile sources of calcium

Abstract

Several studies demonstrate that calcium (Ca) presents low mobility in the phloem, hence it is supplied to plant tissues mainly by the xylem. Since transpiration is the driving force of the xylem flow, Ca supply can be compromised in organs, such as fruits, which have low transpiration rate. Low productivity as well as disorders in fruits, such as apical rot, bitter pit, wilt and reduced shelf life are associated with Ca deficiency. The literature shows that the application of Ca-based foliar fertilizers, or even fruit treatment, can prevent these problems. Conversely, this same literature lacks information about the influence of Ca sources on the rate of leaf absorption and translocation. Likewise, little is known about how the application strategies influence Ca exports to the fruits. Compared with radioisotopes, X-ray fluorescence spectrometry emerges as a simpler, cheaper, and safer alternative that allows monitoring the movement of nutrients in plant tissues. This project aims at employing X-ray fluorescence to determine the absorption and translocation rates of Ca sources applied via foliar treatment. We will test CaCl2, the most common source reported in the literature, as well as chelated Ca with citrate and EDTA. To increase the sensitivity of X-ray fluorescence, strontium (Sr) will be spiked to these sources. Tomato (Solanum lycopersicum) was chosen as model plant for the study. The source of Ca with the greatest translocation capacity in the phloem will be selected in a next phase of the study, evaluating the splitting effects of the application on the productivity and quality of the fruits. The spatial distribution of Ca in the fruits will be measured by X-ray fluorescence mapping. Finally, the mass balance of Ca/Sr foliar applied shall determine the export efficiency of the treatments from the treated leaves to the drain organs. From plant physiology/nutrition standing point, the major expected outputs are: 1) contribute to the understanding of the Ca movement limitation in the phloem; 2) Potential to identify sources with greater mobility than CaCl2; 3) Demonstrate if the application strategies are able to increase the export efficiency of Ca from foliar fertilizers to fruits. Finally, the project also has the aspiration of consolidating X-ray fluorescence spectrometry in plant studies among researchers, and also disseminating foliar nutrition technology to producers. (AU)