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Show COLLEGE OF SCIENCE UNDERGRADUATE RESEARCH ABSTRACTS HOW DO CELLS SEETHE LIGHT? Diego Cordero Cervantes, Jeffrey J. Green, (Darryl L. Kropf) Department of Biology University of Utah Many zygotes and spores of brown algae are photosensitive and establish a developmental axis in accordance with directional light cues. Ectocarpus siliculosus is being advanced as a genetic and genomic model organism for investigating brown alga development, and this report investigates photopolarization of the growth axis of mitospores. W h e n exposed to unidirectional light, mitospores photopolarized and established a growth axis such that germination was preferentially localized to the shaded hemisphere of the spore body. The roles of the microtubule cytoskeleton and endomembrane cycling in the photopolarization process were investigated using pharmacological agents. Disruption of microtubule dynamics progressively reduced the percentage of mitospores that photopolarized, while inhibition of vesicle secretion blocked photopolarization nearly completely. Chronic treatment with these pharmacological agents severely affected algal morphogenesis. Microtubules in mitospores and algal filaments were imaged by confocal microscopy. Mitospores contained a radial microtubule array emanating from a centrosome associated with the nuclear envelope. At germination, the radial array gradually transitioned into a longitudinal array with microtubules extending into the emerging apex. At mitosis, spindles were aligned with the growth axis of cylindrical cells in the filament, and the division plane bisected the spindle axis. These studies demonstrate that dynamic membrane cycling and microtubule assembly play fundamental roles in photopolarization, and provide a foundation for future genetic and genomic investigations of this important developmental process. Unidirectional light with/without drug Overhead light in PES t=Oh: Mitospores placed in dish. _L t=flh, 12h,or 16h: Dish rinsed 5 times with t=day 2-3: Direction of first germ tube recorded. -60 |-50 J-40 o a. |-30 |-20 °--10 0 10 -50 c o is-40 I-30H o 1-20 1-10 ^4 * r +r-{- 12 16 8 12 16 Time in unidirectional light (h) Diego Cordero Cervantes Jeffrey J. Green Darryl L. Kropf 63 |
