Influence of gravity and light on the developmental polarity of Ceratopteris richardii fern spores

Abstract

The polarity of germinating single-celled spores of the fern Ceratopteris richardii Brogn. is influenced by gravity during a time period prior to the first cellular division designated a "polarity-determination window". After this window closes, control of polarity is seen in the downward (with respect to gravity) migration of the nucleus along the proximal face of the spore and the subsequent downward growth of the primary rhizoid. When spores are germinated on a clinostat the direction of nuclear migration and subsequent primary rhizoid growth is random. However, in each case the direction of nuclear migration predicts the direction of rhizoid elongation. Although it is the most obvious movement, the downward migration is not the first movement of the nucleus. During the polarity-determination window, the nucleus moves randomly within a region centered behind the trilete marking. While the polarity of many fern spores has been reported to be controlled by light, spores of C. richardii are the first documented to have their polarity influenced by gravity. Directional white light also affects the polarity of these spores, but this influence is slight and is secondary to that of gravity.

Profile and Analysis of Gene Expression Changes during Early Development in Germinating Spores of Ceratopteris richardii

“…Spores of the fern Ceratopteris richardii of an inbred diploid strain designated Hn-n were surface sterilized as described in Edwards and Roux (1998). Spores were allowed to soak in sterile water in complete darkness at 29°C for 4 to 7 d to enhance synchronization of germination.…”

“…Imbibed spores remain dormant until exposed to light, at which time they begin a documented series of developmental steps, including the production of a detectable polar calcium current that peaks 6 h after light exposure (Chatterjee et al, 2000), migration of the nucleus 24 h after light exposure, a polar cell division 48 h after light exposure, and subsequent primary rhizoid emergence in the direction determined by the nuclear migration 72 h after light exposure. As demonstrated by Edwards and Roux (1998), the spores fix the direction of their nuclear migration and primary rhizoid emergence as a response to gravity in the 6 to 18 h after light exposure. Here, we provide an initial analysis of the mRNA expression that accompanies these physiological changes.…”

“…Ceratopteris has been used to study such diverse processes as sex determination and differentiation (Wen et al, 1999), hormone responses (Hou et al, 2004), photomorphogenesis (Kamachi et al, 2004), and gravity-directed polar development (Edwards and Roux, 1998;Chatterjee et al, 2000). Imbibed spores remain dormant until exposed to light, at which time they begin a documented series of developmental steps, including the production of a detectable polar calcium current that peaks 6 h after light exposure (Chatterjee et al, 2000), migration of the nucleus 24 h after light exposure, a polar cell division 48 h after light exposure, and subsequent primary rhizoid emergence in the direction determined by the nuclear migration 72 h after light exposure.…”

Interactions between Auxin Transport and the Actin Cytoskeleton in Developmental Polarity ofFucus distichusEmbryos in Response to Light and Gravity

“…Although polarized by centrifugation at 3,000g, a 1g stimulation has not been reported to polarize these embryos (Whitaker, 1937;Whitaker, 1940). In contrast, a 1g stimulation is sufficient to polarize single-celled fern spores of Ceratopteris richardii (Edwards and Roux, 1998). Whether and how embryos of brown algae are polarized by gravity remains unknown.…”

Rapid and Efficient Suppression of Gene Expression in a Single-Cell Model System, Ceratopteris richardii

“…The calcium current is followed by downward nuclear migration. This repositioning of the nucleus sets up an asymmetric cell division, creating a bottom cell that emerges as the rhizoid, and an upper cell that develops into the gametophyte thallus (Edwards and Roux, 1998).…”