Studies on the mechanisms responsible for rye cultivar differences in Al resistance

Both aluminum (Al)-induced secretion of organic acids from roots and the immobilization of Al with phosphorus in roots were investigated to elucidate Al-resistant mechanisms in rye (Secale cereale L.，cv. Win and King). It was shown that root elongation rate after Al treatment (10, 30, 50 mol/L) in Win was higher than that in King. Pretreatment with phosphate before Al treatment increased P and Al content in root tips, and Al/P in Win root tips was higher than that in King. These results suggested that the immobilization of Al with phosphorus in root tips was associated with Al resistance mechanism in rye. On the other hand, Al induced the secretion of citrate and malate from roots of both cultivars and, furthermore, the secretion rate was higher in Al-resistant Win than that in Al-sensitive King. The secretion of organic acids increased with increasing Al concentration (10, 30, 50 mol/L) and periods (0.5, 3, 6, 9, 12 h), while the secretion of citrate decreased significantly under low temperature (4℃). The secretion of malate was detected as soon as 0.5 h after Al treatment, while apparent increase in the secretion of citrate could not be detected until 6 h after Al treatment. Phosphorus-deficiency pretreatment for 3 d before Al treatment could not increase the secretion of organic acids. Moreover, the treatment with La3+, Cu2+ or Ni2+ (10 mol/L) failed to induce the secretion. All these results suggested that specific secretion of organic acids from roots was also a mechanism for rye cultivar differences in Al resistance.