Effects of silicic acid analogs on ailica body production and wall ultrastructure in stinging cells of Urtica pillulifera

Abstract

Silicification and cell wall structure in the stinging cell of Urtica pillulifera were studied by electron microscopy. Plants were grown in hydroponic solutions containing various silicon-containing compounds. These compounds included the naturally occurring pre-silica monomer, silicic acid (SA), or one of six silicon-containing analogs, trimethyl silicic acid (TMSA), dimethyl silicic acid (DMSA), methyl silicic acid (MSA), ethyl silicic acid (ESA), hydro silicic acid (HSA), and phenyl silicic acid (0SA), or a combination of DMSA and SA. Silicification in the stinging cell wall normally occurs as primary and secondary silica bodies. None of the analogs permits secondary silica bodies to be formed. When SA is present along with DMSA secondary silica body production is blocked. Primary silica bodies are produced from ESA, 0SA, MSA, and HSA, but not DMSA or TMSA. All of the combination supplements produce distortions of the electron dense patterns in the organic phase of the cell wall. All analogs caused green spots to appear on the leaves and then gradually increase in number on the plant. DMSA totally blocks flowering in the plant; however, this blockage can be overcome if SA is present along with DMSA. Cell wall thickening and normal secondary cell wall morphology are prevented by DMSA and MSA. Cell wall deposition continues until the normal thickness occurs for all of the other analogs, but the cell wall structure is highly modified. These results indicate the involvement of silicon in metabolic processes in addition to silica production, and also allow preliminary correlation of function with the molecular structure of the silicic acid analog.