Visualizing Nutrient Effects on Root Pattern Formation

This lab gives students hands-on experience with visualizing the root architecture of plants exposed to varying concentrations of the vital nutrient phosphorus. By maintaining Brassica sp. seedlings in the presence of different quantities of phosphate, students can quantify changes in the number of lateral roots as an example of how the environment influences plant pattern formation. Additional variables in the experimental design, such as the use of plant mutants altered in plant regulator action or the presence of plant regulators in the plant growth medium, allow for exploration of how plant growth regulators are involved in root development. The quantitative and qualitative nature of this nine-day activity provides instructors opportunities to introduce students to various data analyses in botanical study. Additional ties to plant anatomy and the agricultural use of plant growth regulators that alter root development make this activity a rich source of exploration for broadening student exposure to plants and their development

When CPR is Needed

Column: Practical Pointer

Bacterial Cyanogenesis: Impact on Biotic Interactions

The ability of bacteria to influence organisms that they associate with via metabolite production is one of the hallmarks of microbial interactions. One metabolite of interest is the metabolic poison cyanide. Production of this metabolite is an unique characteristic of certain bacteria that inhabit a wide array of habitats ranging from the human body to the rhizosphere. This review focuses on four targets of cyanogenic bacteria: the human lung, plant pathogens, plants and invertebrates. For a number of cyanogenic bacteria, the contribution of cyanide to the interaction has been rigorously tested using mutants altered in cyanide production. Both deleterious and stimulatory effects of cyanogenic bacteria on other organisms have been documented. In addition, the HCN synthase-encoding gene cluster hcnABC has served as a marker of cyanogenic capability in the soil environment revealing both genetic diversity at this locus and regulatory influences by other organisms. The pervasive nature of cyanogenesis in a number of different ecological contexts encourages exploration of this bacterial ability and its possible optimization for improving human health, crop production and pest control

Weed Suppression by Deleterious Rhizobacteria is Affected by Formulation and Soil Properties

Deleterious rhizobacteria (DRB) suppress weed growth in field tests and are considered potential weed biological control agents. This study compared the relative inhibitory action of the DRB Pseudomonas fluorescens strain G2-11 in different formulations, corn gluten meal (CGM), and semolina flour, toward wheat (Triticum aestivum L.), green foxtail (Setaria viridis (L.) Beauv.), and velvetleaf (Abutilon theophrasti Medik) seeds and seedlings in soil assays. Strain G2-11 successfully established in semolina flour as an inoculum formulation but was incompatible with CGM presumably because of antibacterial factors present. The effect of DRB and plant products on seed germination and plant growth were influenced by soil, with the strongest effects seen in fine sandy loam. Semolina flour alone reduced root growth of all target plants except for velvetleaf in silt loam. Green foxtail seed germination was greatly reduced by strain G2-11. With the exception of wheat seedling growth, strain G2-11 enhanced growth-suppressive qualities of semolina flour. Results suggest that natural plant products such as CGM and semolina flour alone and formulated with selected DRB may be important components for weed management considerations in sustainable agriculture

Influence of Root Colonizing Bacteria on the Defense Responses of Bean

Colonization of plant roots by fluorescent pseudomonads has been correlated with disease suppression. One mechanism may involve altered defense responses in the plant upon colonization. Altered defense responses were observed in bean (Phaseolus vulgaris) inoculated with fluorescent pseudomonads. Systemic effects of root inoculation by Pseudomonas putida isolate Corvallis, P. tolaasii (P9A) and P. aureofaciens REW1-I-1 were observed in bean leaves from 14-day-old plants. SDS- polyacrylamide gel electrophoresis demonstrated that levels of certain acid-soluble proteins increased in the leaf extracts of inoculated plants. Plants inoculated with REW1-I-1 produced more of a 57 Mr protein, and plants inoculated with isolates P9A and REW1-I-1 produced more of a 38 Mr protein. Northern hybridization revealed enhanced accumulation of mRNAs, that encode the pathogenesis-related protein PR1a, in leaves of plants inoculated with P. putida and REW1-I-1. Only REW1-I-1, but not P9A or P. putida induced symptoms of an hypersensitive response on tobacco leaves, bean cotyledons, and in bean suspension cultures. Phenolics and phytoalexins accumulated in bean cotyledons exposed to REW1-I-1 for 24 h but little change in levels of these compounds occurred in cotyledons inoculated with P9A and P. putida. Both suspension culture cells and roots treated with REW1-I-1 rapidly evolved more hydrogen peroxide than those exposed to P9A and P. putida. However, roots from 14-day-old plants colonized by P9A, P. putida or REW1-I-1 did not have higher levels of phenolics, phytoalexins or mRNAs for two enzymes involved in phenolic biosynthesis, phenylalanine-ammonia lyase and chalcone synthase. A selective induction of plant defense strategies upon root colonization by certain pseudomonads is apparent. © 1992, Kluwer Academic Publishers. All rights reserved

Differential Rhizosphere Establishment and Cyanide Production by Alginate-formulated Weed-deleterious Rhizobacteria

The effects of Pseudomonas putida ATH2-1RI/9 and Acidovorax delafieldii ATH2-2RS/1 on rhizosphere colonization, cyanide production, and growth of velvetleaf and corn was examined. When formulated in alginate beads and inoculated onto velvetleaf and corn plants (109 CFU/plant), only P. putida ATH2-1RI/9 consistently reduced velvetleaf growth. Neither isolate inhibited corn growth. Interestingly the levels of P. putida ATH2-1RI/9 in the velvetleaf rhizosphere were 1000-fold higher (7 × 107 CFU/g root) than the A. delafieldii ATH2-2RS/1 populations. Cyanide (53-68 mM/g root) was recovered from the P. putida ATH2-1RI/9-inoculated velvetleaf plants. In contrast both A. delafieldii ATH2-2RS/1 and P. putida ATH2-1RI/9 colonized the corn rhizosphere to the same extent (1-5 × 107 CFU/g root), producing 1 mM and 14 mM/g root respectively. These results suggest that bacterial formulation methods can influence the effectiveness of deleterious rhizobacteria in reducing weed growth. © Springer Science+Business Media, Inc. 2005

Approaches to student success in introductory biology

The Department of Biology has implemented several approaches to increase student success in the majors-level introductory biology course, BIOL165. First, a three-day program during freshman orientation week provided students with tips and skills for success, exposure to specific class content and opportunities to develop comradery, but it did not result in significant learning gains in the participants. Second, a team-based learning approach was developed to emphasize active learning and personal interactions in the classroom; this approach had limited success with students who entered with weak study skills. Finally, a supplemental study strategies class was offered to struggling students. Students self-reported implementation of and appreciation for selected study strategies. While the evaluation of impact on student learning was difficult to assess, each approach had unique aspects that targeted particular learning needs

Inhibition of Seed Germination and Induction of Systemic Disease Resistance by Pseudomonas chlororaphis O6 Requires Phenazine Production Regulated by the Flobal Regulator, GacS

Seed coating by a phenazine-producing bacterium, Pseudomonas chlororaphis O6, induced dose-dependent inhibition of germination in wheat and barley seeds, but did not inhibit germination of rice or cucumber seeds. In wheat seedlings grown from inoculated seeds, phenazine production levels near the seed were higher than in the roots. Deletion of the gacS gene reduced transcription from the genes required for phenazine synthesis, the regulatory phzI gene and the biosynthetic phzA gene. The inhibition of seed germination and the induction of systemic disease resistance against a bacterial soft-rot pathogen, Erwinia carotovora subsp. carotovora, were impaired in the gacS and phzA mutants of P. chlororaphis O6. Culture filtrates of the gacS and phzA mutants of P. chlororaphis O6 did not inhibit seed germination of wheat, whereas that of the wild-type was inhibitory. Our results showed that the production of phenazines by P. chlororaphis O6 was correlated with reduced germination of barley and wheat seeds, and the level of systemic resistance in tobacco against E. carotovora. © The Korean Society for Microbiology and Biotechnology