Accumulation and localization of aluminium in root tips of loblolly pine seedlings and the associated ectomycorrhiza Pisolithus tinctorius

ABSTRACT Evidence from past studies suggests that loblolly pine maybe tolerant of Al. The experiments described in this manu-script were initiated to examine Al tolerance and Al accu-mulation in the pine root and the degree of Alaccumulation in fungal hyphae when pine roots were colo-nized with the ectomycorrhiza Pisolithus tinctorius. Theexperiments used lumogallion staining and confocalmicroscopy to localize Al in root and fungal structures. Theresults clearly showed that loblolly pine seedlings werehighly resistant to Al. A decrease in primary root extensioncould not be detected until Al +3 activities approached40 m mol L - 1 , and extension was suppressed only 30% at anAl +3 activity of 580 m mol L - 1 . This contrasted with theresponse of the Al-sensitive ‘check’ species soybean, whereprimary root extension was severely restricted at Al +3 activ-ities lower than 5 m mol L - 1 . Tissue Al measurements andlumogallion fluorescence of longitudinal sections of thepine root tip indicated that tolerance was associated withboth Al exclusion from the tip region and compartmental-ization of absorbed Al in peripheral cell areas outside ofthe meristem. In lateral roots colonized with ectomycor-rhizae, lumogallion fluorescence showed that large amountsof Al accumulated at the fungal mantle and in areas withthe Hartig net. At higher magnification, lumogallion indi-cated substantial Al accumulation inside hyphae. Little Alcould be detected in lateral root cells. The results show thatpine possesses multiple mechanisms that can contribute toAl tolerance in acid field soils.Key-words: Pisolithus tinctorius; confocal scanning micros-copy; lumogallion.