Biological Sciences
Presenter(s): Alexandros Drivas
Advisor(s): Dr. Gregory Goldsmith, Dr. Carter Berry
Drought-induced plant stress is known to interfere with plant function, growth and ultimately contribute to plant mortality. Beyond a certain threshold of water loss, the water in the xylem tissue of the plant experiences excessive tension and air bubbles are formed. These air bubbles are known as embolisms and lead to the death of the plant. Our understanding of the factors affecting embolism formation in response to drought however, remain limited. I have developed a new device capable of coupling measurements of plant gas exchange via infrared gas analysis to measurements of embolism based on digital images. The device is simple, in that it couples to existing commercially available technologies. This device will allow us to carry out simultaneous and real-time measurements of plant water use and embolism in plant leaves under controlled environmental conditions. For instance, the device provides us with the ability to study the influence of environmental factors such as relative humidity, CO2 levels, temperature, and light intensity, on plant gas exchange and embolism. Currently, no device is capable of collecting data relating embolism formation to any of these variables allowing us to go past many current technological limitations. Further development and modifications have been made to increase the device’s energy efficiency, resolution of the images, and ease of use. I have begun translating pieces of the device into 6061 Aluminum. Further manufacturing of the device in 6061 Aluminum will increase measurement accuracy and precision, particularly by addressing the need to maintain consistent air pressure in the device’s sample chamber. The completion of the device will allow the scientific community to make measurements that ultimately inform our ability to mitigate the negative consequences of drought for plants in both natural and agricultural settings.
Time of Day Dependence in Plant-Rhizobia Interaction
Presenter(s): Teresa Hur, Yoobeen Lee, Isaac Min, Ashley Okhovat, Sydni Au Hoy, Kenjiro Quides
Advisor(s): Dr. Hagop S. Atamian
In nature, plants interact with diverse microorganisms present in the soil. Some of these interactions are mutualistic, where both the plant and the soil microorganism benefit from the interaction. Legumes have established a unique mutualistic relationship with soil bacteria known as rhizobia. As part of this interaction, rhizobia enter the plant root and get housed in special structures on the root called nodules. Once established inside the nodule, rhizobia fix atmospheric nitrogen for the plant host in return for photosynthetic carbon. The plant interaction with the rhizobia greatly enhances plant productivity as they get access to usable form of nitrogen which is the most limiting macronutrient in agricultural production. However, this relationship between the plant and bacteria is very intricate and is influenced by many factors such as the plant variety, rhizobia species, soil nutrient composition, and ambient temperature. The objective of this project is to investigate the effect of time of the day on this interaction. Both plants and animals have internal biological clock that keep track of the time in the outside environment and accordingly adjust various physiological processes. We investigated the success of legume-rhizobia association by introducing the rhizobia to the plant every four-hour interval during a single day in a pouch system. Seeds of Lotus japonicus were germinated in growth pouches in sterile condition and grown for two weeks in 16 hr light/ 8 hr dark photoperiod under controlled environment. Mesorhizobium loti was cultured on a plate and a suspension of 10 billion cells/ml was prepared. The roots of two-week-old L. japonicus were inoculated with the bacterial suspension starting at dawn (ZT0) and every 4 hours until ZT20 (20 hours after dawn). Our results showed time of day effect in this interaction, where the interaction happened most efficiently at ZT12. The results from this project will help us better understand the complexity of this relationship and enable us to device new approaches to increase crop productivity.
Identification and Characterization of Plant Defensins Family Genes in Salvia Hispanica
Presenter(s): Megan Shieh
Advisor(s): Dr. Hagop S. Atamian
Being sessile organisms, plants rely on very sophisticated defense mechanisms to survive the constant challenges in nature. These include physical and chemical defenses in addition to complex immune responses. Plant defensins (PDFs) are a family of small (45-55 amino acid) cysteine-rich peptides that play important roles in plant immune responses. PDFs are conserved peptides that are widely distributed in plants and constitute a large and diverse family as part of the overall plant pathogenesis-related proteins. PDFs possess wide range of biological activities that are effective against bacteria, fungi, insects, and viruses. Interestingly, some PDFs have been shown to possess anticancer and cytotoxicity effects. Salvia hispanica, commonly known as chia, belongs to the mint family (Lameaceae). The mint family is a diverse family of flowering plants with more than 7,000 species identified to date. Being an understudied plant species that was recently rediscovered as a healthy food supplement for humans and nutritious feed source for animals, not much is known about the immunity related genes and their evolution in chia plants. The objective of this project is to identify and characterize the members of plant defensins family in chia. Based on sequence similarity, using the sequence alignment program DIAMOND, we identified chia homologs of the PDF genes characterized in number of plant species. We constructed phylogentic trees using the Maximum Likelihood (ML) approach to identify the phylogenetic relationships of candidate chia PDFs to those identified in other plant species. In addition, we analyzed the expression of a subset of chia PDFs in response to bacterial attack. The results from this project will represent the first comprehensive analysis of this important and diverse gene family in salvia hispanica.