In land plants, two distinct generations, gametophyte and sporophyte, alternate to complete the life cycle. Sporophytes undergo meiosis to produce spores, from which gametophytes develop. Gametophytes produce gametes, which participate in fertilization to produce the zygote, the first cell of the sporophyte generation. In addition to this sexual reproduction pathway, some fern species can undergo apospory or apogamy, processes that bypass meiosis or fertilization, respectively, to alternate between the two generations without changing the chromosome number. Apospory is inducible in the laboratory in various fern species simply by altering the sugar level in the media. In sporophytes induced to undergo apospory, sporophyte regeneration is also observed. The ratio of aposporous gametophytes to regenerated sporophytes varies, in a manner consistent with being dependent on sugar level. Whereas the sugar signaling pathway is yet to be elucidated in lower plants, in angiosperms it has been shown to play a regulatory role in controlling essential processes including flowering and embryo development, which give rise to the gametophyte and the next sporophyte generation, respectively. Here, we present evidence for the role of different sugar levels on the balance of apospory and regeneration in the fern Ceratopteris richardii. The demonstration of crosstalk between sugar signaling and the hormone ethylene signaling in angiosperms prompted us to test the effects of this hormone in combination with sugar on apospory vs. regeneration. These results provide insight into how a group of redifferentiating cells determines which generation to become and lay the groundwork for further analysis of this asexual pathway.
COVID-19's impact on society and our daily habits has been unprecedented. With a decrease in vehicular traffic and industrial production, a decrease in local emissions was expected to occur. In order to capture any trends in ambient trace gas concentrations, approximately one thousand whole air samples were collected in intervals across the United States from April to July 2020 as part of the NASA Student Airborne Research Program (SARP). These samples were then analyzed by the UCI Rowland-Blake Lab using multi-column gas chromatography for over one hundred unique trace gases, including methane, non-methane hydrocarbons, and halocarbons, as described in Colman et al. (2001) and Barletta et al. (2002). Initial samples collected in April coincided with the peak of stay-at-home/social distancing orders in most states while samples collected later in the spring and early summer reflect the easing of these measures and initial state reopenings. Overall trends in emissions over time in select metropolitan areas will be discussed and compared to trends observed across the entire United States.
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