Cell Wall Pectin and its Binding Capacity Contribute to Aluminium Resistance in Buckwheat

Buckwheat (Fagopyrum esculentum Moench) cultivars differred in aluminum (Al) resistance were selected to investigate the possible role of cell wall pectin content and its binding capacity to Al in Al resistance. Al contents in root apices of Al-resistant cultivars were lower than those in Al-sensitive cultivars, suggesting the Al exclusion mechanism was acting in Al-resistant buckwheat cultivars. We observed that pectin contents in Al-resistant cv. Jiangxi were significantly lower than those in other three cultivars, irrespective of with or without Al treatment. Further investigation was conducted with the most Al resistant cv. Jiangxi and Al sensitive cv. Yq3h. Pectin and Al contents were higher in Yq3h than those in Jiangxi from 0-5 and 5-10 mm root sections. After 6-h exposure to 50 muM Al, 48% and 60% of the Al were retained in the cell wall for Jiangxi and Yq3h, respectively. Consequently, more Al was removed by 30-min citrate desorption in Yq3h. The kinetics study with cell wall extracted from 0-5 mm root section showed that the total amount of Al adsorbed was higher and the desorption rate was lower in Yq3h than those in Jiangxi, suggesting that cell walls in Yq3h could bind more Al and the bound Al was retained more tightly compared with Jiangxi. From all these results, we concluded that the differences in cell wall pectin content and its binding capacity to Al contribute to the genotypic differences in Al resistance in buckwheat.