Apolar Embryos of Fucus Resulting From Osmotic and Chemical Treatment

Abstract

Embryos of the brown alga Fucus vesiculosas L. were grown as populations in glass petri dishes in seawater at 15 C in continuous low‐intensity unilateral fluorescent illumination for periods up to 2 weeks. A quantitative estimate of increase in nuclear number was made from acetocarmine squash preparations of samples taken at 12‐or‐24 hr intervals. Over the period of 2‐6 days embryos showed a doubling time of about 12‐18 hr. Under normal seawater culture conditions each embryo formed a single rhizoid. When grown in seawater supplemented with sugar concentrations above 0.4 m, Fucus embryos developed as multicellular spherical embryos lacking rhizoids. In 0.6 m sucrose‐seawater, 97% of the embryos were apolar at 2 days; only 37% were apolar at 4 days, many having recovered from the sucrose inhibition. Some embryos remained apolar after growth in 0.6 m sucrose for 2 weeks. Nuclear counts showed that sucrose‐seawater markedly inhibited the rate of cell division. Other sugars including D‐glucose, D‐fructose, D‐galactose and the sugar alcohol D‐mannitol were also effective. When apolar embryos grown in sucrose‐seawater were returned to seawater, embryo growth resumed at the normal seawater rate, judged from nuclear counts. Such embryos formed multiple rhizoids, varying from two to eight rhizoids per embryo, which developed on the embryo quadrant or half away from the unilateral light. Each of the multiple rhizoids originated from a single small cell in the periphery of the multicellular spherica embryo. Thus the rhizoid‐forming stimulus apparently had been subdivided among a number of the cells of the apolar embryos. The implications of this finding are discussed. Attempts to produce multiple rhizoids by treatment of embryos with indoleacetic acid or 2,4‐dichlorophen‐oxyacetic acid failed. However, embryos treated with 10−4 M or 5 × 10−5 m 2,3,5‐triiodobenzoic acid formed 40 and 30% multiple rhizoids, respectively, suggesting that some chemical, perhaps hormonal, mechanism is involved in polarization and rhizoid initiation in Fucus embryogenesis.

Early Embryo Development in Fucus distichusIs Auxin Sensitive

“…Although most F. distichus rhizoids will ultimately form branches, these normally occur much later in development and in cells considerably further from the thallus cell. If IAA and NPA treatments are performed in the light, the magnitude of these developmental alterations are significantly reduced (data not shown), which is consistent with a previous report in which IAA had no significant effects and an IAA efflux inhibitor had only slight effects on F. distichus embryo development in the light (Torrey and Galun, 1970). Because F. distichus embryos normally are released and undergo the earliest stages of development in the light, the physiological relevance of these developmental effects of exogenous IAA and NPA should be considered.…”

Ionic requirements for establishment of an embryonic axis in Pelvetia zygotes

“…Previous reports also indicated that zygotes photopolarize in hypertonic ASW (Torrey and Galun 1970;Quatrano 1973). We cannot, however, rule out the possibility that minimal turgor pressure, not detectable by observation of plasmolysis, is needed for photopolarization.…”

Reproductive ecology, of Fucus distichus (Phaeophyceae):an intertidal alga with successful external fertilization

“…Both hyper-and hypoosmotic conditions can potentially affect gamete release and fertilization, since receptacles from a single alga may be near both the top and bottom of a pool's water colun~n. After settlement, potential hyperosmotic stress is more important, because zygotes remain near the bottom of the pools: it is known that osmolalities within the range of those measured in the tide pools inhibit the expression of polarity in Fucus vesiculosus for up to 14 d (Torrey & Galun 1970). In their experiments, Torrey & Galun used sucrose as osmoticum, but zygotes in seawater of similar osmolality will presumably be exposed to the added stress of potentially cytotoxic intracellular concentrations of ions.…”