THE INTERACTION BETWEEN SILICON AND ALUMINUM IN SORGHUM-BICOLOR (L) MOENCH - GROWTH ANALYSIS AND X-RAY-MICROANALYSIS

Seeds of Sorghum bicolor (L.) Moench. were germinated on moist filter paper for 6 d, before the seedlings were transferred to pots containing (formula presented). The seedlings were then treated with (formula presented) in factorial combination with (formula presented). The background solution used throughout was (formula presented). 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: (formula presented) only; (formula presented) only; and a combination of the two. In the (formula presented) treatment silica was deposited in the endodermis, with the greatest accumulation being in the inner tangential wall (ITW). When plants were treated with (formula presented) 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 (formula presented) 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. © 1993 Annals of Botany Company.