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Defective apical growth, timing of initiation of polar growth, and hormone response in a Physcomitrella patens insertional mutant


Cell and Molecular Biology


College of Liberal Arts and Sciences

Date Range



Medicine and Health Sciences


Following injury, Physcomitrella patens filaments re-establish polar growth to produce chloronema filaments. Subsequent tip cell differentiation results in caulonema filaments, on which an initial cell is initiated on the second subapical cell. This cell, while still small, is capable of responding to high levels of cytokinin to result in the formation of leafy gametophores, completing the switch from 2-D to 3-D growth to enable sexual reproduction. We have been characterizing a random insertional mutant unable to make this switch. The insertion is located in the genome between a retrotransposon-related sequence and a 10 bp tandemly repeated sequence; it does not appear to have disrupted coding sequence. We have examined the re-establishment of polar growth and subsequent development under two different conditions after protoplasting and mechanical fragmentation (MF) of filaments and then grown on nutrient-rich medium. In both cases, we found polar growth is established in the mutant, albeit at a much slower rate and there is a delay in tip cell differentiation. We also confirmed the establishment of initial cells, the result of new initiation of polar growth, on the first subapical cell rather than on the second, and the subsequent inability of the mutant to produce leafy gametophores. In addition, using MF tissue, the mutant showed the most dramatic response when grown on nutrient-rich medium plus auxin. Short, chloronema-like filaments with club-shaped tip cells resulted. These had multiple initiations of initial cells, even on the tip cells themselves. Under nutrient-poor conditions, the mutant showed a delay in tip cell differentiation and an increase in undulating growth, both enhanced in the presence of auxin. Overall, these analyses suggest a defect in many facets of tip growth, some of which are sensitive to auxin, due presumably to disruption of regulatory sequence in the genome.

Conference Name

Margaret Dietrich

Conference Location

Portland OR, United States

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