Role of cotyledons in aluminium accumulation as a tolerance strategy in Fagopyrum esculentum Moench (Polygonaceae) seedlings.

Acidic soils have increased due to agricultural practices, climate factors, and the excessive use of nitrogen fertilizers to meet food demand. In these soils, aluminium (Al) is soluble and can be taken up by roots, but it is toxic to most plant species. Fagopyrum esculentum is able to adapt to acidic toxic aluminium conditions. Anatomical studies identifying novel potential cellular structures as sites of Al accumulation are currently lacking. This study provides an anatomical description of the cotyledons, revealing the presence of papillae and glandular trichomes at their margins. In seedlings treated with 100 μM Al, energy-dispersive x-ray spectroscopy (ESEM-EDS) analysis of the cotyledons revealed that the margin has the highest concentration of Al. The margin containing the epidermal papillae was subjected to laser microdissection, and Al was quantified using mass spectrometry with an inductively coupled plasma source ICP-MS and compared with the Al in the remaining leaf blades. The concentration of Al in the microdissected papillae was 3,460 mg Al kg^-1 Dry Weight (DW), whereas the blades contained only 1,390 mg Al kg^-1 DW. Moreover, histochemical tests for Al and total phenols in the epidermal papillae revealed that Al may be bound to phenolic compounds. Thus, this study demonstrated that the cotyledons of F. esculentum have epidermal papillae that can accumulate Al.