Microbial Growth in Shrimp Ponds as Influenced by Monosilicic and Polysilicic Acids

In order to increase shrimp production and minimize detrimental environmental impacts of aquaculture, the maintenance and regulation of the growth and composition of phytoplankton communities and nutritional balance are critical. Silicon (Si) is an essential nutrient for diatoms and other types of microorganisms, but the information about the Si impact on their growth is extremely scarce. Monosilicic and polysilicic acids were tested in several shrimp cultivation systems in Jiangsu Province, China. In pond waters, the concentrations of monosilicic and polysilicic acids sharply reduced by 36–95% and 35–75%, accordingly, as compared with those in supply water sources. The microbial cell abundance was strongly dependent on monosilicic acid, while the correlation with polysilicic acid was absent. In laboratory experiments, monosilicic acid added to pond water or probiotic solution at 1 and 2 mM Si had a significant positive effect on cell abundance. Over three days, the concentrations of monosilicic acid decreased by 81 to 91% in pond water and by 11 to 24% in probiotic solution. In probiotic solutions, the degree of polymerization of silicic acid was more intensive than that in shrimp pond waters. The data obtained demonstrates the importance of systematic studies related to the functions of Si in shrimp aquaculture.

Learning Principles in the Biochemistry of Plant Silica Precipitation

<p>Plants produce silica in large quantities, up to 2-10% per dry weight, depending on growth conditions and plant species. The roots absorb monosilicic acid from the soil, and it is transported with water and distributed in nearly all plant tissues. With evapotranspiration, the silicic acid solution is concentrated, and eventually silica forms at leaf epidermis. Nonetheless, the distribution of silica deposits is not uniform within plant tissues. This suggests that there are biological processes that control the deposition of the mineral. In a recent work, the protein Siliplant1 (Slp1) was discovered to precipitate silica in plants. Slp1 is expressed in sorghum leaf epidermal cells called silica cells. Biological molecules active in silica formation typically present positive charge moieties and form some 3D aggregation pattern that allows monosilicic acid to condense into bigger organized structures. Slp1 contains a 24 amino acid N-terminal signal peptide, followed by 124 amino acid linking sequence and a 7-repeat sequence. Slp1 without the signal peptide and a short, conserved peptide appearing five times in Slp1 precipitate silica <em>in vitro</em>. However, the activity of other parts of Slp1 in silica precipitation remains unknown. To analyze sequence motifs that precipitate silica, we synthesized segments of the repeating sequence in Slp1, and characterized the precipitation reactions by yield and spectroscopy. Thermal gravimetric and electron microscopy analyses are planned. Preliminary results show that the most conserved region in the repeating sequence precipitates silica at a concentration range of 1-1.5 mg/mL in a 100 mM silicic acid solution. Under buffered conditions, this peptide is positively charged, precipitating silica at pH between 6 and 7. In contrast, silica-gel formed at pH 8 or 5 after overnight incubation. In comparison, the full length Slp1 (missing the signal peptide) precipitates silica at an estimated concentration of 2.9 mg/mL and pH 6-8. Peptides flanking the conserved sequence did not precipitate silica. Precipitation reactions with combinations of peptides precipitated silica only when the conserved peptide was mixed with the peptide following it at a 1:1 ratio. This part of Slp1 presents –OH moieties that may interact with silica. The reaction produced silica gel as well as silica. When the conserved region was mixed with a preceding peptide, only silica-gel formed. This region presents acidic groups that may block the positive charge on the conserved region. We conclude that the conserved peptide is the only part of the Slp1 repeating region that actively precipitates silica. The peptides flanking the conserved region are not directly involved in silica precipitation.  However, they may allow silica precipitation at increased pH, as seen in the full length Slp1. Further investigation is planned to understand their roles in silica formation.</p>

Silicon increases chlorophyll and photosynthesis and improves height and NDVI of cotton (Gossypium hirsutum L. r. latifolium Hutch)

Silicon (Si) it is a beneficial element that relieves biotic and abiotic stresses in plants. However, cotton plants are not considered Si accumulators, with low potential for uptake the element by roots. The objective of this study was to evaluate the effect of combinations of Si rates applied by leaf spray and soil on the physiology, growth and yield of cotton (Gossypium hirsutum L. r. latifolium Hutch). The experimental design was a randomized complete block in a 3 x 4 factorial scheme with four replications. Leaf spraying consisted of three Si concentrations (0, 500, and 1000 mL ha-1) corresponding to 0, 100, and 200 ml ha-1 of monosilicic acid, with spraying split into three applications at stages V4, V6 and V8. Soil-based fertilization consisted of four Si rates in (0, 2.5, 5.0, and 10.0 kg ha-1) corresponding to 0, 0.5, 1.0, and 2.0 kg ha-1 of SiO2. At flowering, photosynthesis, green color index (GCI), plant height, and NDVI were evaluated. The application of Si in the planting furrow near the rhizosphere increased the green color index, reflecting a gain in photosynthesis and plant height, which positively increased NDVI. The use of high solubility Si in the planting furrow can increase the concentration of monosilicic acid in the area with the highest root distribution, enhancing the effect of this element in a non-accumulator crop such as cotton, by improving the green color index, photosynthesis and hence reflecting on gains in plant height and plant leaf area demonstrated by NDVI.