The interaction between silicon and aluminium in Sorghum bicolor (L.) Moench: growth analysis and X-ray microanalysis
1993
Hodson, M.J. | Sangster, A.G.
Seeds of Sorghum bicolor (L.) Moench. were germinated on moist filter paper for 6 d, before the seedlings were transferred to pots containing 500 micromoles l-1 Ca(NO3)2 for 2 d. The seedlings were then treated with 0 or 100 micromoles l-1 Al in factorial combination with 0, 1400 or 2800 micromoles l-1 Si for 8 d. The background solution used throughout was 500 micromoles l-1 Ca(NO3)2. Aluminium treatment reduced root growth and caused a significant increase in shoot/root ratio. The presence of silica in the solution significantly ameliorated the effects of aluminium on root growth. Three treatments were selected for a microanalytical investigation of the basal region of the root: 2800 micromoles l-1 Si only; 100 micromoles l-1 Al only; and a combination of the two. In the 2800 micromoles l-1 treatment silica was deposited in the endodermis, with the greatest accumulation being in the inner tangential wall (ITW). When plants were treated with 100 micromoles l-1 Al only, aluminium concentration was highest in the outer tangential wall (OTW) of the epidermis. The element was present in the hypodermal walls and OTW of the endodermis and was not detectable in the stele. With both 2800 micromoles l-1 Si and 100 micromoles l-1 Al in the nutrient solution the two biomineralization sites were the ITW of the endodermis, where silicon was the major element deposited, and atypically in the OTW of the epidermis where both aluminium and silicon were present. The sequestration of aluminium in the Al-Si deposit in the OTW of the epidermis may represent the mechanism that allows greater root growth in this treatment.
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