Observations on the Distribution of Mineral Elements in the Leaf of Wheat (Triticum aestivum L.), with Particular Reference to Silicon

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Abstract
Wheat (Triticum aestivum L. cv. Wheaton) plants were grown in water culture or in soil. Basal leaves (B) were harvested after 3 weeks from the water culture plants, while flag leaves were collected from soil-grown material at the time of inflorescence emergence (E0) and 7 d after emergence (E + 7). Mineral distribution in bulk frozen leaves was investigated using SEM and X-ray microanalysis. The elements detected were silicon, phosphorus, chlorine, sulphur, potassium and calcium. Potassium was present in all cell types at all harvests, chlorine was almost entirely confined to the adaxial and abaxial epidermi, while sulphur was only rarely detected in the E0 and E + 7 leaves. Phosphorus was present at higher levels in the E + 7 leaves than in the B or E0 leaves. At the B harvest calcium was confined to the adaxial epidermal cells, but in the E0 and E + 7 leaves it was present in both epidermi. Silicon was, initially, mainly detected in the abaxial epidermal cells, but in older (E + 7) leaves it was present in both epidermi and in some internal tissues. Mineral transport within the leaf and ionic environment at silica deposition sites are discussed.