Intracellular Silica Deposition in Immature Leaves in Three Species of the Gramineae

The formation of solid, discrete deposits of opaline silicawithin the cell lumen of leaf tissues is reported in speciesrepresenting three subfamilies of the Gramineae; the preparationof a silica-minimal nutrient solution is discussed. Opal phytolithnumbers are related to tissue age and to two external silicaconcentrations for tiller leaves over a period of 32 days followingbud initiation. Variations in silica deposition patterns among the individualleaves of a homologous series on the shoot apex are relatedto differential growth-rates. During ontogeny, deposition occursin an ordered sequence of cell types related to the basipetalmaturation gradient within the leaf. Initial deposition wasdetected in silica cells (idioblasts) of imbricated, bud leavesof Sieglingia decumbens, 1 mm long; phytoliths are confinedto these cells in expanding, basal portions of the leaf. Phytolithcounts/sq mm of epidermis vary with the degree of long-cellexpansion. The error is reduced by expressing silicificationas the number of phytoliths/100 silica cells. Post-expansiondeposition was initiated in epidermal long cells of the leafblade tip. The higher silica concentration resulted in a morerapid utilization of available deposition sites and larger phytoliths(P = 0.001). A passive cell influx of silicic acid is discussedin relation to cytodifferentiation.