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Transmission electron microscopy of leaves of sweet orange trees grafted on Swingle (A–C) or Sunki (D–F) rootstocks grown in nutrient solution with varying concentrations of B for 130 days. Concentration of nutrient solution, in mg L-1 of boron: left (0.01), center (0.5), and right (5.0) columns. Legend: SG, starch grains; Ch, chloroplast; arrow, unstructured chloroplast.
