Location of seed coat split prior to germination: An SEM investigation of Zostera marina seed

Background/Question/Methods

To obtain Zostera marina seed stock we collected flowering shoots from False Bay, San Juan Island in September 2010. Shoots were placed in a flowing seawater mesocosm and examined periodically. Released seed was immediately placed in seawater filled vials and stored at 5 degrees C.  Before SEM analysis seeds were fixed in F.A.A. (formalin, acetic acid, and ethyl alcohol) in which filtered seawater was substituted for distilled water. Staining was done using either Conantʼs Quadruple Stain or Fosterʼs Ferric Chloride, Tannic Acid and Safranin method. We then used a Neoscope JMC 5000 to investigate fine scale seed detail.

Results/Conclusions

We noticed that there were a variety of horizontal cracks in the seed coat and wondered if they aided in the splitting of the seed coat during germination.

Our examination showed that cracks on the seed coat may not aid in the splitting of the seed coat and that the seed coat probably splits along the ridges as suggested by Taylor (1955). We also found that the seed coat appears to split at the micropyle where according to Taylor the seed coat is exceptionally thin. The splits that run along the ridges widen until the embryo emerges.