title: Aluminum Tolerance in Wheat (Triticum aestivum L.) (I. Uptake and Distribution of Aluminum in Root Apices).
abstract: We investigated the uptake and distribution of Al in root apices of near-isogenic wheat (Triticum aestivum L.) lines differing in Al tolerance at a single locus (Alt1: aluminum tolerance). Seedlings were grown in nutrient solution that contained 100 [mu]M Al, and the roots were subsequently stained with hematoxylin, a compound that binds Al in vitro to form a colored complex. Root apices of Al-sensitive genotypes stained after short exposures to Al (10 min and 1 h), whereas apices of Al-tolerant seedlings showed less intense staining after equivalent exposures. Differential staining preceded differences observed in either root elongation or total Al concentrations of root apices (terminal 2-3 mm of root). After 4 h of exposure to 100 [mu]M Al in nutrient solution, Al-sensitive genotypes accumulated more total Al in root apices than Al-tolerant genotypes, and the differences became more marked with time. Analysis of freeze-dried root apices by x-ray microanalysis showed that Al entered root apices of Al-sensitive plants and accumulated in the epidermal layer and in the cortical layer immediately below the epidermis. Long-term exposure of sensitive apices to Al (24 h) resulted in a distribution of Al coinciding with the absence of K. Quantitation of Al in the cortical layer showed that sensitive apices accumulated 5- to 10-fold more Al than tolerant apices exposed to Al solutions for equivalent times. These data are consistent with the hypothesis that Alt1 encodes a mechanism that excludes Al from root apices.
authors.affiliation: Division of Plant Industry, Commonwealth Scientific and Industrial Research Organization, GPO Box 1600, Canberra ACT 2601, Australia (E.D., S.C., V.C.J., P.J.R.).
authors.forename: E.
authors.initials: E
authors.lastname: Delhaize
authors.forename: S.
authors.initials: S
authors.lastname: Craig
authors.forename: C. D.
authors.initials: CD
authors.lastname: Beaton
authors.forename: R. J.
authors.initials: RJ
authors.lastname: Bennet
authors.forename: V. C.
authors.initials: VC
authors.lastname: Jagadish
authors.forename: P. J.
authors.initials: PJ
authors.lastname: Randall