The Chemical Nature of Silica in Plants.

Abstract

Silica has longf been known to be present in plants. Richardson (6) reported its abundance in the aerial parts of plants of the Equisetum genus and many Gramineae, constituting 50 to 70 % of the ash. He also stated that of all elements found in plants, silicon showved the greatest variation between plant parts, plants, and species of plants. Silicon usually occurs in plants in the form of its oxide, SiO2, commonly called silica.Although the presence of silica has been established its chemical form in higher plants has not been reported. This study was conducted primarily to provide such information. Since opal and a quartz are produced and exist as minerals at temperatures favorable to plant growth one might expect that silica in plants would be one or the other or both.According to Iler (2) the solubility of amorphous silica at ordinary temperatures is most commonly reported to be about 0.010 to 0.015 %. Esau (1) stated that some plants absorb more silica than they need and inasmuch as it cannot be excreted, it is deposited in the tissues. In general, the more water absorbed by a plant, the greater the amount of silica deposited. Silica is deposited mostly in cell walls, but sometimes as bodies in the lumen of the cell. The Gramineae is the best known group depositing silica; the deposition takes place in both cell walls and cell lumina. Silica is not usually deposited in underground parts.In this work the silica was characterized by chemical analysis, petrographic microscope studies, and x-ray diffraction analysis. The petrographic microscope was used for the initial identification of the type of silica present. The optical characteristics of opal and quartz are quite different so that this method of study is readily used to differentiate between them. X-ray diffraction studies were conducted to supplement the information gained by the petrographic microscope and to show the presence of minor constituents. The x-ray diffraction pattern of a quartz has been determined by Swanson and Fuyat (7) and x-rav studies of opal have been made by Swineford and Franks (8).This study has also established: (A) unreported types of silica deposition and (B) tissues other than the epidermis as sites of silica deposition. Spodograms were used for this purpose as they are the best method for studying the sites and depositional pattern of silica in situ. Spodograms are made by mounting ash material on microscope slides. The process was developed by Uber (9) and. used by Molisch (3) and Ohki (4) to get distinct, transparent

Leaf anatomy of three herbaceous bamboo species

“…Campos & Labouriau (1969) assume that silica plays an important role in hydric balance, thermic changes and radiation reflection. Besides, Lanning et al (1958) and Moore (1984) state that silica is a complementary structural element, contributing to vegetative support.…”

Contributions of Forest Opal and Associated Crystalline Phases to Fine Silt and Clay Fractions of Soils

“…Lewin (1961) and Jones and Handreck (1963) have found evidence that Fe and A1 are chemisorbed to opaline ,surfaces, thereby retarding subsequent silica dissolution. Further, it has been shown that opaline constituents undergo partial or full conversion to chalcedony upon aging in soils and geologic sediments (Beavers and Stephen, 1958;Yarilova, 1952;Mizutani, 1967) 9 Several workers have presented X-ray evidence of cristobalite, trydimite, or quartz in opaline isolates of vegetative tissues but generally attributed 295 such crystalline phases to artifacts produced by dryashing isolation procedures (Lanning et al, 1958;Jones and Milne, 1963;Arimura and Kanno, 1965).…”

Rendimento e acúmulo de nutrientes pelo arroz em solução nutritiva com e sem a adição de silício

“…O Si(OH) 4 é prontamente absorvido pelas plantas e, apesar de não ser considerado um elemento essencial, algumas espécies o absorvem em quantidades comparáveis ou bem superiores a macronutrientes essenciais (Marschner, 1995). Praticamente, todo o Si absorvido é translocado das raízes para as folhas e, com a saída da água pela transpiração, polimeriza na parte externa da parede celular (principalmente nas células da epiderme), transformando-se em um mineral amorfo de sílica denominado opala biogênica (SiO 2 .nH 2 O) (Lanning et al, 1958). As plantas diferem quanto à absorção de Si, sendo divididas em acumuladoras, intermediárias e não-acumuladoras, conforme o total de Si absorvido e a quantidade do elemento fornecida por fluxo de massa (Marschner, 1995).…”