Seedlings ofTriticum aestivumL. (cv. Celtic) were suspended in plastic tubs containing 500 μmol L−1Ca(NO3)2and 31 μmol L−1KC1 as background solution. A1C13(0 and 100 μmol L−1) and Na2SiO3.5H2O (0 and 2000 μmol; L−1) were added to this basal nutrient medium, and solution 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 °C with a 16 h photoperiod. At pH 4.2 and 4.6 root length of the seedlings was inhibited at 100 μmol L−1Al. An amelioration of Al-induced toxicity symptoms was observed in the 100 μmol L−1A1/2000 μmol L−1Si treatment at pH 4.6, but not at pH 4.2. Both the shoot (S) and root (R) dry weight of seedlings treated with 100 μmol L−1Al were reduced when compared with controls. Treatment with Al increased S:R ratios, and this effect was ameliorated by Si, but only at pH 4.6.Al content of roots treated with 100 μmol L−1Al or 100 μmol L−1Al/2000 μmol L−1Si increased significantly when compared with controls. More Al accumulated in the roots of seedlings of the 100 μmol L−1Al/2000 μmol L−1Si treatment than in the 100 μmol L−1treatment. 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 treatments were selected for a microanalytical investigation of the basal third of the root, and the zone 3.5 mm behind the root tip: 2800 μmol L−1Si; 75 μmol Al; and a combination of the two. When plants were grown in 2800 μmol L−1Si the major silica deposition sites in the roots were the endodermal walls. In the 75 μmol L−1Al treatment, Al was mainly located in the epidermal and hypodermal walls. Al treatment caused a leakage of phosphorus into these cell walls. When both 2800 μmol L−1and 75 μmol L−1Al were present in the nutrient solution, only Si was deposited in the endodermal walls, while both elements were present in the epidermal walls. Leakage of phosphorus appeared to be prevented in the presence of Si.
Investigation of Hemicellulose Alteration in Fabaceae Root Cell Walls During Flooding-Induced Aerenchyma Formation