TITANIUM DIOXIDE NANOPARTICLES AFFECT THE GROWTH AND MIRNA EXPRESSION OF SWITCHGRASS (PANICUM VIRGATUM)

Abstract

Nanoparticle TiO2 is a common chemical used in paint, plastic, paper, ceramics, coated fabrics, floor coverings, printing ink, roofing granules, cosmetics, dyes and even food and drugs. As increasing usage of TiO2, it is becoming a potentially dangerous contaminant to the environment. However, the impact of TiO2 is not well understood. In this paper, switchgrass, an important biofuel crop, was employed to investigate the impact of nanoparticle TiO2 on plant growth and development as well as the potential impact on the expression of microRNAs (miRNAs), important gene regulators. Our results show that TiO2 significantly affected switchgrass seed generations as well as plant growth and development in a dose-dependent manner. Particularly, TiO2 significantly inhabited root development. MiRNA expressions were also significantly altered. Nanoparticle TiO2 may regulate plant development through controlling the expression of certain miRNAs. Among the 16 tested miRNAs, the expression of some miRNAs, such as miR390 and miR399 was increased with increasing TiO2 concentration; the expression of some miRNAs, such as mi169 was decreased with increasing TiO2 concentration; the other miRNAs show different expression patterns. For the second part of this paper, our objective was to improve tissue culture medium to produce switchgrass callus. As the global need for biofuel increases so does the need for efficient tissue culture and transformation systems of bio-feedstock. Here we show the effects of Zeatin (ZT) and 2,4-Dichlorophenoxyacetic acid (2,4-D) on switchgrass seeds to investigate which combination of cytokinins and auxins will result in an effective embryogenic callus induction culture for switchgrass (Panicum virgatum). Switchgrass seed were cultured on MS media containing concentrations of 2,4-D ranging from 0 mg/l to 5 mg/l in combination with Zeating concentrations of 0 mg/l, 0.1 mg/l and 0.5 mg/l. Over 400 embryogenic calli were obtained where the most plants obtained in the treatment contained 1.0 mg/L 2,4-D and 0.5 mg/L ZT after the calli were transferred to the regeneration media. The results of this experiment indicate that, zeatin, in conjunction with 2,4-Dichlorophenoxyacetic acid (2,4-D), can produce a viable callus induction media for switchgrass.