Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item INVESTIGATING THE REGULATION OF GROWTH MECHANISMS IN TWO DISTINCT BRANCHES OF PHOTOSYNTHETIC LIFE(2019) Sittmann, John; Liu, Zhongchi; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Photosynthetic organisms often have limited mobility and rely on a variety of environmental, physiological, and chemical signals to regulate aspects of growth and development. In this thesis, I investigated how two such organisms, one a flowering plant and the other a heterokont alga, incorporate external signaling cues to make decisions regarding reproduction. My dissertation research is focused on 1) investigating molecular mechanisms of crosstalk between photoperiod and shade in regulating asexual reproduction in the wild strawberry Fragaria vesca, and 2) elucidating the mechanism of a bacterium-derived agent in the stimulation of cell division in the marine diatom Phaeodactylum tricornutum. First, strawberry, including woodland strawberry Fragaria vesca, is capable of a form of asexual reproduction by producing horizontal stems with daughter plants at the nodes. These horizontal stems, referred to as stolon, are derived from axillary meristems at the base of the leaves. Depending on the signals the axillary meristem receives, it will give rise to either a branch crown (a flowering shoot) or a stolon. Stolon allows for asexual reproduction to maintain the superior hybrid genotype and hence is of great significance agriculturally. Daughter plants derived from stolon are sold and propagated in strawberry farming. In this work, I have shown that a key regulatory protein FveRGA1 in GA signaling pathway functions as a repressor of stolon development. I further expanded this work by showing that the light quality (shade) signaling pathway interacts with the GA signaling to regulate stolon development. I identified and demonstrated FvePIF3 as a key transcription factor that positively regulates stolon initiation under far-red light (shade). Understanding the mechanisms underlying axillary meristem cell fate determination could advance biotechnology to increase strawberry production. Second, I have discovered and characterized a bacterium-based growth stimulation of the diatom Phaeodactylum tricornutum. Specifically, I noticed that a culture of P. tricornutum that had been accidentally contaminated with bacteria exhibited faster growth. I subsequently identified the responsible bacterium as Bacillus sp, which stimulated rapid Phaeodactylum cell division when added to the Phaeodactylum culture. I experimentally determined that the growth stimulating agent was heat labile and proteinase K-resistant. Further, I showed that the mother cell lysate of Bacillus sp. under sporulation was just as effective in promoting Phaeodactylum. In collaboration with Dr. Jon Clardy lab, we identified the growth-stimulating compounds as two distinct peptide-signaling molecules. The work revealed that the peptides may be previously under-reported signaling molecules for cross-kingdom communications. In addition to the fundamental discovery of novel signaling mechanisms between bacterium and algae, this work may facilitate large-scale diatom culture in biomass production for biofuel and biopharma.Item Ecological and geomorphological impacts of channel stability restoration in urban streams(2011) Laub, Brian Guthrie; Palmer, Margaret A; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stream restoration projects that attempt to reduce channel incision and bank erosion by reconstructing the channel and grading and armoring stream banks (channel stability restoration projects) are common, particularly in urbanized watersheds. However, integrated assessment of changes in geomorphic processes and ecological properties within the channel and in the surrounding riparian zone induced by stability restoration has rarely been carried out across multiple restored streams. I provide such an assessment by measuring channel complexity, bed sediment dynamics, channel movement rates, riparian soil structure and function, and diatom communities in multiple restored streams located in urbanized watersheds and comparing these measurements to measurements from urban and forested reference streams. Stability restoration appears to have reduced lateral channel migration and channel incision through channel reshaping. Patterns of bed sediment movement were altered through the effects of added channel obstructions on flow dynamics and bed sediment size distribution. Channel stability restoration did not alter channel complexity, primarily because channel complexity was not reduced by urbanization as has commonly been assumed. Restoration did not alter diatom communities either, primarily because diatom communities responded more strongly to urbanization-induced changes in water chemistry. Riparian soils were negatively impacted by stability restoration, particularly compared to riparian buffer establishment, which had mostly neutral effects on riparian soils. Channel stability restoration can provide a minor increase in channel and bed sediment stability. However, changes in bed sediment stability were driven by in-channel restoration structures, which can be placed without grading the banks or reconstructing the channel. Riparian buffer restoration can also stabilize channels and will provide wood to channels, which can provide similar stabilization benefits as restoration structures. Restoration of channel stability using only in-channel structures and riparian vegetation planting would reduce the cost of stability restoration and reduce negative impacts to riparian soils. Even so, effects of stability restoration were often overwhelmed by processes operating beyond the channel boundaries, suggesting that reach-scale targeting of channel instability needs to be assessed at the watershed scale and may need to be given lower priority to such restoration approaches as stormwater management, which directly address the causes of channel instability.