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Danville, VA, United States

Sunny M.R.,Virginia Polytechnic Institute and State University | Kapania R.K.,Virginia Polytechnic Institute and State University | Moffitt R.D.,Institute for Advanced Learning and Research | Mishra A.,Johns Hopkins University | Goulbourne N.,Virginia Polytechnic Institute and State University
Journal of Applied Mechanics, Transactions ASME | Year: 2010

This paper describes the development of a fractional calculus approach to model the hysteretic behavior shown by the variation in electrical resistances with strain in conductive polymers. Experiments have been carried out on a conductive polymer nanocomposite sample to study its resistance-strain variation under strain varying with time in a triangular manner. A combined fractional derivative and integer order integral model and a fractional integral model (with two submodels) have been developed to simulate this behavior. The efficiency of these models has been discussed by comparing the results, obtained using these models, with the experimental data. It has been shown that by using only a few parameters, the hysteretic behavior of such materials can be modeled using the fractional calculus with some modifications. © 2010 by ASME. Source

Dan Y.,Institute for Advanced Learning and Research | Dan Y.,Virginia Polytechnic Institute and State University | Zhang S.,Institute for Advanced Learning and Research | Zhong H.,Syngenta Biotechnology | And 2 more authors.
Plant Cell Reports | Year: 2014

Key message: Agrobacteriumtumefacienscaused tissue browning leading to subsequent cell death in plant transformation and novel anti-oxidative compounds enhancedAgrobacterium-mediated plant transformation by mitigating oxidative stress.Abstract: Browning and death of cells transformed with Agrobacterium tumefaciens is a long-standing and high impact problem in plant transformation and the agricultural biotechnology industry, severely limiting the production of transgenic plants. Using our tomato cv. MicroTom transformation system, we demonstrated that Agrobacterium caused tissue browning (TB) leading to subsequent cell death by our correlation study. Without an antioxidant (lipoic acid, LA) TB was severe and associated with high levels of GUS transient expression and low stable transformation frequency (STF). LA addition shifted the curve in that most TB was intermediate and associated with the highest levels of GUS transient expression and STF. We evaluated 18 novel anti-oxidative compounds for their potential to enhance Agrobacterium-mediated transformation, by screening for TB reduction and monitoring GUS transient expression. Promising compounds were further evaluated for their effect on MicroTom and soybean STF. Among twelve non-antioxidant compounds, seven and five significantly (P < 0.05) reduced TB and increased STF, respectively. Among six antioxidants four of them significantly reduced TB and five of them significantly increased STF. The most efficient compound found to increase STF was melatonin (MEL, an antioxidant). Optimal concentrations and stages to use MEL in transformation were determined, and Southern blot analysis showed that T-DNA integration was not affected by MEL. The ability of diverse compounds with different anti-oxidative mechanisms can reduce Agrobacterium-mediated TB and increase STF, strongly supporting that oxidative stress is an important limiting factor in Agrobacterium-mediated transformation and the limiting factor can be controlled by these compounds at different levels. © 2014, Springer-Verlag Berlin Heidelberg. Source

Dan Y.,Institute for Advanced Learning and Research | Dan Y.,Virginia Polytechnic Institute and State University | Zhang S.,Institute for Advanced Learning and Research | Matherly A.,Institute for Advanced Learning and Research
Plant Cell, Tissue and Organ Culture | Year: 2016

Our previous studies demonstrate that Agrobacterium causes tissue browning that subsequently reduces transformation efficiency in tomato transformation. In addition application of lipoic acid (LA) can reduce tissue browning and increase transformation efficiency in different crops. A major challenge in Agrobacterium-mediated plant transformation is the death of Agrobacterium-transformed cells (DATC), which restricts transgenic plant production. Hydrogen peroxide (H2O2) plays a critical role in oxidative stress. However, little is known about the biochemical and molecular mechanisms for DATC. Our biological and correlation analyses showed that Agrobacterium mediated H2O2 accumulation (HOA) and HOA elevation led to DATC during Agrobacterium-mediated tomato cv. MicroTom transformation. Agrobacterium significantly (P < 0.05) increased 4.2- and 1.4-fold expression of WRKY75 (a H2O2-responsive transcription factor) and superoxide dismutase (SOD), respectively, while the application of 4.4 M H2O2 significantly increased 19- and 2.7-fold expression of WRKY75 and 2-cys peroxiredoxin (Cys), respectively, and decreased fivefold SOD expression, compared with a control. LA application significantly (P < 0.05) reduced 1.6-fold HOA and DATC while it significantly increased 1.7-fold expression of Cys, and reduced 2.2- and 1.4-fold expression of WRKY75 and SOD, respectively. The reduction of HOA and DATC was accompanied by suppression of WRKY75 and SOD and activation of Cys. Our results indicated that DATC was regulated by H2O2 that was triggered by Agrobacterium and LA application through their gene regulation. In addition, HOA was associated with a biotic generating reactive oxygen species (ROS) mechanism, and HOA and DATC were likely regulated by an enzymatic ROS scavenging mechanism during Agrobacterium-mediated tomato transformation. © 2016 Springer Science+Business Media Dordrecht Source

Garda M.,Arkansas State University | Devaiah S.P.,Arkansas State University | Devaiah S.P.,East Tennessee State University | Vicuna Requesens D.,Arkansas State University | And 7 more authors.
Transgenic Research | Year: 2015

Transgenic plants in the US and abroad generated using genetic engineering technology are regulated with respect to release into the environment and inclusion into diets of humans and animals. For crops incorporating pharmaceuticals or industrial enzymes regulations are even more stringent. Notifications are not allowed for movement and release, therefore a permit is required. However, growing under permit is cumbersome and more expensive than open, non- regulated growth. Thus, when the genetically engineered pharmaceutical or industrial crop is ready for scale-up, achieving non-regulated status is critical. Regulatory compliance in the US comprises petitioning the appropriate agencies for permission for environmental release and feeding trials. For release without yearly permits, a petition for allowing non-regulated status can be filed with the United States Department of Agriculture with consultations that include the Food and Drug Administration and possibly the Environmental Protection Agency, the latter if the plant includes an incorporated pesticide. The data package should ensure that the plants are substantially equivalent in every parameter except for the engineered trait. We undertook a preliminary study on transgenic maize field-grown hybrids that express one of two cellulase genes, an exo-cellulase or an endo-cellulase. We performed field observations of whole plants and numerous in vitro analyses of grain. Although some minor differences were observed when comparing genetically engineered hybrid plants to control wild type hybrids, no significant differences were seen. © 2014, Springer International Publishing Switzerland. Source

Veilleux R.E.,Virginia Polytechnic Institute and State University | Oosumi T.,Virginia Polytechnic Institute and State University | Wadl P.A.,Virginia Polytechnic Institute and State University | Baxter A.J.,Virginia Polytechnic Institute and State University | And 7 more authors.
Acta Horticulturae | Year: 2012

Insertional mutant collections are essential tools in plant genomic research and functional genomics. Extensive collections in Arabidopsis and rice are used to gain intimate knowledge of gene function. These collections are less useful for understanding gene function and expression of native genes associated with the development of fleshy fruit that comprise the edible product of many horticultural crops. We have therefore undertaken a program to develop an insertional mutant collection of the diploid strawberry, Fragaria vesca, as a model crop for fleshy fruit. An accession of F. vesca has been selected for photoperiod insensitivity, short life cycle (16-20 weeks from seed to seed) and facility of Agrobacterium-mediated leaf explant transformation. We are currently evaluating several hundred insertional mutants bearing the GFP reporter gene and hygromycin resistance for antibiotic selection. Single gene insertional mutants in the T1 generation have expressed unusual phenotypes for leaf morphology, anthocyanin development, flower morphology and plant habit. Interrupted genes that control the expression of these mutant phenotypes have been revealed by analysis of flanking regions adjacent to T-DNA insertions through TAIL-PCR. Gene discovery resulting from current and future analyses of the mutant collection may lead to development of transgenic or cisgenic fruit crops that have various commercial advantages. Source

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