INTERACTION BETWEEN SILICON AND ALUMINUM IN TRITICUM-AESTIVUM L. (CV CELTIC)

Seedlings of Triticum aestivum L. (cv. Celtic) eere suspended in plast ic tubs containing 500 mu mol L-1 Ca(NO3)(2) and 31 mu mol L-1 KCl as background solution. AlCl3 (0 and 100 mu mol L-1) and Na2SiO3.5H(2)O ( 0 and 2000 mu mol L-1) were added to this basal nutrient medium, and s olution pH was set at 4.2 or 4.6. Tubs were aerated and supplied with a continuous flow of pH-adjusted test solution. Plants were grown for 4 d in a growth cabinet at 25 degrees C with a 16 h photoperiod. At pH 4.2 and 4.6 root length of the seedlings was inhibited at 100 mu mol L-1 Al. An amelioration of Al-induced toxicity symptoms was observed i n the 100 mu mol L-1 Al/2000 mu mol L-1 Si treatment at pH 4.6, but no t at pH 4.2. Both the shoot (S) and root (R) dry a eight of seedlings treated with 100 mu mol L-1 Al were reduced when compared with control s. Treatment with Al increased S:R ratios, and this effect was amelior ated by Si, but only at pH 4.6. Al content of roots treated with 100 m u mol L-1 Al or 100 mu mol L-1 Al/2000 mu mol L-1 Si increased signifi cantly when compared with controls. More Al accumulated in the roots o f seedlings of the 100 mu mol L-1 Al/2000 mu mol L-1 Si treatment than in the 100 mu mol L-1 treatment. Al treatment reduced root and shoot K concentrations under both pH regimes, and Si did not ameliorate this effect. Al treatment had little effect on seedling Ca levels. Three t reatments were selected for a microanalytical investigation of the bas al third of the root, and the zone 3.5 mm behind the root tip: 2800 mu mol L-1 Si; 75 mu mol L-1 Al; and a combination of the two. When plan ts were grown in 2800 mu mol L-1 Si the major silica deposition sites in the roots were the endodermal walls. In the 75 mu mol L-1 Al treatm ent, Al was mainly located in the epidermal and hypodermal walls. Al t reatment caused a leakage of phosphorus into these cell walls. When bo th 2800 mu mol L-1 Si and 75 mu mol L-1 Al were present in the nutrien t solution, only Si was deposited in the endodermal walls, while both elements were present in the epidermal walls. Leakage of phosphorus ap peared to be prevented in the presence of Si.