ALUMINUM STRESS INHIBITS ACCUMULATION OF PHOSPHORUS IN ROOT APICES OF ALUMINUM-SENSITIVE BUT NOT ALUMINUM-RESISTANT BRACHIARIA CULTIVAR

ABSTRACT

The phosphorus (P) content of whole roots and root apices has been reported to increase under aluminum (Al) stress, particularly in Al-sensitive plant varieties. We investigated the impact of Al toxicity on the P content of root apices of two tropical forage cultivars of the Brachiaria genus, grown in Al-containing low-ionic-strength nutrient solutions. Exposure to Al did not affect apical P concentrations in Al-resistant B. decumbens cv. Basilisk. In contrast to previous results obtained with other plant species, however, it caused a 70% decline in the apical P content of Al-sensitive B. ruziziensis cv. Common, despite the simultaneously increasing P levels in older root portions. This effect was largely due to a reduced accumulation of organically bound P, because less than 7% of the P in root apices was in the inorganic form in either species or treatment. The P content of root apices might be a useful indicator for evaluating the resistance of Brachiaria cultivars to prolonged Al stress.

ACKNOWLEDGMENTS

This work was funded by the Kommission für Entwicklungsfragen of the Austrian Academy of Sciences, and by the Colombian Ministry of Agriculture and Rural Development.