Theses and Dissertations from UMD
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Item MOLECULAR MECHANISMS OF PLANT RESPONSES TO COLD, HEAT AND SALT STRESSES IN ARABIDOPSIS(2013) Guan, Qingmei; Zhu, Jianhua; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Abiotic stresses, such as temperature extremes and salinity adversely affect plant productivity and distribution worldwide. Resistant or susceptible to stresses is a complex trait because more than one stress may occur simultaneously, for example, salinity is accompanied with ion toxicity and water deficit. To survive in a fixed environment, plants have to adjust their metabolisms and developmental programs to adapt to the stress or acclimate to the transitory stress. The responses of plants to different abiotic stresses are extremely complex, involving stress perception, signaling transduction, and response induction. We took a forward genetic analysis approach and identified three novel proteins in the reference plant Arabidopsis thaliana, Regulator of CBF Gene Expression 1 (RCF1), Regulator of CBF Gene Expression 3 (RCF3), and Short Root in Salt Medium 3 (RSA3), which are critical for plant tolerance to cold, heat and salinity, respectively. RCF1 is a cold-inducible DEAD box RNA helicase protein which is localized in the nucleus. RCF1 is a positive regulator for chilling and freezing tolerance. RCF1 functions to maintain proper splicing of pre-mRNAs because many cold-responsive genes are mis-spliced in rcf1-1 mutant plants under cold stress. RCF3 encodes a KH-domain containing putative RNA-binding protein. RCF3 is a negative regulator of most heat stress transcription factors (HSFs). Consistent with the overall increased accumulation of heat-responsive genes, the rcf3 mutants are heat-tolerant. RSA3, a xylogluscan galactosyltransferase, is essential for salt stress tolerance. rsa3-1 mutant plants are hypersensitive to NaCl and LiCl but not to CsCl or to general osmotic stress. RSA3 controls expression of many genes including genes encoding proteins for reactive oxygen species (ROS) detoxification under salt stress. RSA3 functions to maintaining the proper organization of actin microfilaments in order to minimize damage caused by excessive ROS. miRNAs play important regulatory roles in plants by targeting messenger RNAs (mRNAs) for cleavage or translational repression. We determined role of the heat-inducible miR398 in plant heat stress tolerance. Our results suggest that plants use a previously unrecognized strategy to achieve thermotolerance, especially for the protection of reproductive tissues. This strategy involves the down-regulation of two copper/zinc superoxide dismutase (CSDs) and their copper chaperone CCS through the heat-inducible miR398.Item EFFECTS OF ABIOTIC STRESS AND PREDATOR REFUGE ON TERRESTRIAL PREDATOR-PREY INTERACTIONS(2009) Lewis, Danny; Denno, Robert F.; Gruner, Daniel; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A major goal of ecology has been to understand how abiotic stress modifies species interactions, including predation. In marine habitats, a well-supported hypothesis holds that stress reduces the importance of predation because predators are more vulnerable to stress than prey, but this hypothesis has not been well-tested in terrestrial systems. The effect of refuge from stress on predation level has been studied even less, particularly in terrestrial systems. My research examines the effects of two types of stress, and refuge from them, on predation in a terrestrial salt-marsh food web. I investigated the stress of winter weather and asked first, whether the top predator used a particular marsh habitat as a winter refuge, second, how inter-year variation in winter severity affected refuge use, and third, how refuge use affected the predator's spatial distribution later in the year (Chapter 1). I found that spring predator density was higher within the refuge than outside, a difference that increased following colder winters. Consequently, predators were forced to re-colonize the rest of the marsh from the winter refuge, creating a long-lasting density gradient with lower densities farther from the refuge. In contrast, prey densities were not affected by winter temperatures, and were higher outside the refuge. This prey distribution may have facilitated predator colonization of non-refuge habitats. I investigated the stress of tidal inundation on marsh predators and prey, and their use of vegetation above water as a refuge from submersion. I found that densities of two key predators were more highly correlated with refuge availability than with tidal intensity. Notably, this correlation with refuge increased during the highest tides of the month. In contrast, distribution of the most abundant herbivore was not correlated with refuge availability (Chapter 2). These results suggested that tides impacted predators more than herbivores, but that refuge negated tidal effects on predators. To test these hypotheses, I eliminated tidal inundation from experimental field mesocosms while allowing control mesocosms to experience normal tides (Chapter 3). I found that tides caused substantial mortality at all trophic levels, but affected predators significantly more than herbivores and decreased predation levels.