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Keywords:

  • boron translocation;
  • deliquescence relative humidity;
  • Glycine max;
  • Litchi chinensis;
  • sorbitol

Abstract

Experiments to assess the rate of absorption and translocation of foliar-applied, isotopically labeled boric acid (BA) were carried out with lychee (Litchi chinensis Sonn.) and soybean (Glycine max [L.] Merr.) plants. Boron (B) absorption and translocation within the plant, one week after treatment, was investigated after adding to the boric acid (BA solutions 0.5 mM CaCl2 and/or 50 or 500 mM sorbitol). The contribution of stomata to the absorption process was assessed by applying the solutions either to the adaxial or to the abaxial leaf side. Both plant species differed greatly in total absorption rates. The adaxial leaf surface (lacking stomata) of lychee leaves was nearly impermeable, while the stomatous abaxial surface was permeable to BA solutions. In this species, no translocation of 10B to other leaf parts and no effect of adjuvants in increasing 10B absorption were recorded. In contrast, 10B was absorbed both by adaxial and abaxial leaf surfaces of soybean leaves. Boron concentrations measured in treated soybean leaves were sixfold higher after application to the abaxial as compared to the adaxial leaf surface. The addition of adjuvants significantly enhanced the rate of 10B absorption, but not its translocation within the plant. Treatments containing 500 mM sorbitol led to increased 10B absorption and enhanced acropetal 10B movement, whereas adding only 50 mM sorbitol had no significant effect. Application of 0.5 mM CaCl2 in combination with 500 mM sorbitol decreased the rate of 10B absorption, compared to the performance of 500 mM sorbitol alone. Basipetal 10B translocation was very limited. A distinct effect of B-sorbitol complexes on B translocation apart from the pure adjuvant effect could not be discerned in this investigation.