Radiocesium uptake through leaf surfaces of tea plants (Camellia sinensis L.)

Highlights: • ¹³⁷Cs applied to front and backside of tea leaves to assess transfer to new shoots. • In the frontside treatment, 95% of ¹³⁷Cs remained in the mature leaves. • 22 and 10% of ¹³⁷Cs found in new shoots and other plant parts of backside treatment. • ¹³⁷Cs primarily absorbed through the backside of leaves through the stoma. • ¹³⁷Cs transported to newly emerged tea organs during new growth period. - Abstract: To clarify the source of radiocesium detected in newly emerged tea leaves contaminated just before the time of bud opening by fallout of radionuclides from Fukushima Dai-ichi Nuclear Power Plant, ¹³⁷CsCl solution (0.185 M Bq mL⁻¹) was applied to the front or the backside surfaces of mature leaves of tea plant (Camellia sinensis L. cv. Yabukita) at the time of bud opening. A 21 days after foliar application, the buds had grown and developed to the three- or four-leaf stage. In the front treatment, almost all (95%) of the applied ¹³⁷Cs was present in the mature leaves (hot mother leaves). In the backside treatment, 68% of applied ¹³⁷Cs also remained in hot mother leaves, but 22% and 10% was found in the new shoots attached to hot mother leaves and the other parts (non-applied mature leaves, stems and roots), respectively. The images of a hot leaf and its attached new shoots by imaging plate analysis revealed that the results coincided with those of the ¹³⁷Cs distribution above. These suggested that radiocesium was primarily absorbed from the backside surface of tea leaves through the stoma, and then the greater part was transported to newly emerged tea organs during the new shoot growth period.