Abstract
Aluminium (Al) toxicity is a major factor reducing crop productivity worldwide. There is a broad variation in intra- and inter-specific Al resistance. Whereas the Al resistance mechanisms have generally been well explored in Al-excluding plant species, Al resistance through Al accumulation and Al tolerance is not yet well understood. Therefore, a set of 94 genotypes from three Fagopyrum species with special emphasis on F. esculentum Moench were screened, with the objective of identifying genotypes with greatly differing Al accumulation capacity. The genotypes were grown in Al-enriched peat-based substrate for 21 days. Based on the Al concentration of the xylem sap, which varied by a factor of five, only quantitative but not qualitative genotypic differences in Al accumulation could be identified. Aluminium and citrate and Al and Fe concentrations in the xylem sap were positively correlated suggesting that Fe and Al are loaded into and transported in the xylem through related mechanisms. In a nutrient solution experiment using six selected F. esculentum genotypes differing in Al and citrate concentrations in the xylem sap the significant correlation between Al and iron transport in the xylem could be confirmed. Inhibition of root elongation by Al was highly significantly correlated with root oxalate-exudation and leaf Al accumulation. This suggests that Al-activated oxalate exudation and rapid transport of Al to the shoot are prerequisites for the protection of the root apoplast from Al injury and thus overall Al resistance and Al accumulation in buckwheat.
Highlights
Acid soils represent a significant percentage of the world’s arable lands [1]
In a recent study comparing Al tolerance and Al accumulation of three Fagopyrum species (F. esculentum, F. tataricum, F. homotropicum) reference [27] concluded that Al accumulation is a conserved trait in Fagopyrum
Shoot Al accumulation was highly significantly correlated with Al resistance indicating that Al accumulation and Al tolerance contribute to overall
Summary
Acid soils represent a significant percentage of the world’s arable lands [1]. Aluminium toxicity is one of the major constrains for crop production on acid soils [2]. Al exclusion through sequestration of Al in the root apoplast with organic acid anions released from the root symplast is the most common mechanism of Al resistance [9]. ). Among the six genotypes Al resistance was highly significantly positively correlated with Al-induced root oxalate-exudation (Table 1). Evaluating the role of both oxalate exudation and Al accumulation in Al resistance using multiple regression analysis (Table 1) revealed that more than 70% (r2 = 0.725 ***) of the variation in Al-induced root-growth inhibition can be explained by these two variables. It appears that both Al exclusion by oxalate root-exudation and rapid oxalate-facilitated Al uptake and citrate-facilitated Al translocation to the shoot are involved in the protection of the root-tip apoplast, the main target of Al rhizotoxicity as elaborated by reference [42].
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