LOCALIZATION OF ALUMINUM IN ROOT APEX CELLS OF 2 AUSTRALIAN PERENNIALGRASSES BY X-RAY-MICROANALYSIS

To determine if an increased aluminium (Al) sensitivity is the result of greater accumulation of Al in root apices, the quantity and distrib ution of Al in root apex cells of Danthonia linkii Kunth and Microlaen a stipoides (Labill.) R.Br. was investigated by X-ray microanalysis. S eedlings were grown in nutrient solution with 0, 185 and 370 mu M tota l Al for 24 h after which the terminal 5 mm of the roots were excised, rapidly frozen and embedded using freeze-substitution. Elemental dist ribution maps of root apices showed that Al had accumulated in the nuc lei of root cap and meristematic cells in Al-stressed roots of D, link ii but not in M. stipoides. Al appeared to be co-localised with phosph orous (P) in the nuclei of these cells. Quantitation of Al revealed th at Al-stressed root apex cells of D, linkii accumulated significantly more Al than M. stipoides. Exposure of D. linkii roots to Al resulted in substantial increases in the P content of root apex cells, and a si gnificant positive correlation was found between Al and P in both root cap and meristematic cells. Analysis of intracellular structures show ed that the majority of Al had accumulated in the nuclei of cells. A s ignificant positive correlation was found between Al and P in the nucl ei, but not in the cytoplasm or cell walls. No positive correlation wa s found between Al and P in root apex cells of M. stipoides.