The accumulation of boron (B) in the lower parts of the plants often leads to a deficiency of boron in the meristematic tissues, a prevalent issue in plants with low boron mobility. The application of B-binding metabolites as growth stimulators facilitates the re-translocation of boron from mature leaves to growing leaves. We assume that the foliar application of these compounds along with boron can efficiently mobilize boron in low boron mobility plants and increase their biomass. This research aims to investigate the differences in boron concentration across various plant parts, while also analyzing the relationship between different forms of boron and their re-mobilization. This will be analyzed in the context of applying ascorbic acid, glycine, and mannitol to spinach. A factorial experiment was conducted in a completely randomized design with three replications. Mature leaves were sprayed with ascorbic acid (A), glycine (G), and mannitol (M) at concentrations of 0, 500, and 1000 mg L− 1, with and without the addition of boron (0.6 mg pot− 1). The results revealed that higher concentrations of glycine and ascorbic acid, whether in the presence or absence of boron, increased the plant’s dry weight. However, plant biomass was not significantly affected by mannitol. Ascorbic acid, glycine, and mannitol, in the presence of boron, reduced the boron concentration in mature leaves and increased the boron concentration in young leaves and roots. Mannitol was more effective than glycine and ascorbic acid in forming boron complexes and its transfer into the phloem. Furthermore, in treatments with high boron mobility (M500 + B and M1000 + B), a greater portion of the total boron was cell-wall-bound B in mature leaves, whereas water-soluble B accounted for a larger portion of total boron in young leaves. This study showed that foliar application of boron and B-binding metabolites together can be considered an efficient method in the B fertilization program in plants with low mobility. Mannitol application had a greater role in boron re-translocation while glycine and ascorbic acid performed better as growth stimulants.

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