EFFECT OF ALUMINUM ON ROOT ELONGATION IN 2 AUSTRALIAN PERENNIAL GRASSES

Inhibition of net root elongation and patterns of hematoxylin staining were used to assess relative tolerance to phytotoxic Al in Danthonia linkii Kunth and Microlaena stipoides (Labill.) R.Br. According to net root elongation, M. stipoides is significantly more tolerant of phyto toxic Al than D. linkii. In nutrient solutions with Al concentrations of 370 mu M and higher, root elongation is stopped in D. linkii after 24 h while in M. stipoides root elongation is maintained at 60-70% of control rates over 72 h. After removal of Al-stress, root growth in M. stipoides from all Al-treatments recovered to be at or above control growth after 72 h. In D. linkii, root elongation in plants exposed to Al levels that caused a reduction in growth (<370 mu M), but not compl ete cessation, recovered after removal of Al stress. Greater intensiti es of hematoxylin staining were seen in Al-stressed root tips of D. li nkii compared to M. stipoides, suggesting that inhibition of root elon gation is associated with increased accumulation of Al in root tips. R oots of M. stipoides seedlings exposed to all Al-treatments showed a s hort band of intensely stained tissue, correlating with the position o f the root apex at the exact point of initial Al-exposure. New root gr owth after this band did not stain with hematoxylin, indicating activa tion of a mechanism of Al-exclusion in roots of M. stipoides.