Development in embryonic leaves of Setaria viridis

Setaria viridis is being promoted as a model C4 photosynthetic plant because it has a small genome (~515Mb), a short life cycle (~60d) and it can be transformed. Unlike other C4 grasses such as maize, however, there is very little information about how C4 leaf anatomy (Kranz anatomy) develops in S. viridis. As a foundation for future developmental genetic studies, Junqueira and colleagues provide an anatomical and ultrastructural framework of early shoot development in S. viridis, focusing on the initiation of Kranz anatomy in seed leaves.

Scanning electron microscopy of <em>S. viridis</em> diaspore during germination from dry seed
Scanning electron microscopy of S. viridis diaspore during germination from dry seed to 36 h after imbibition (first embryonic leaf rupturing the coleoptile). (A) Stage S0 – dry seed – with bracts: first glume (*), second glume (**), sterile lemma (arrow) and fertile lemma (dashed arrow) enveloping the caryopsis (the palea remains covered by the sterile lemma). (B) Stage S1 – 12 h after imbibition, the coleorhiza rupturing the caryopsis (arrow). (C) Stage S2 – 15 h after imbibition, absorbent hairs of the coleorhiza (arrow) are visible. (D) Stage S3 – 24 h after imbibition, coleoptile breaking through the caryopsis (arrow); the radicle (*), the mesocotyl (dashed arrow) and coleorhiza (**) are visible. (E) Stage S4 – 36 h after imbibition, left: intact coleoptile; right: the first juvenile leaf has ruptured the coleoptile (arrow). (F) Ruptured coleoptile shown in detail. Scale bar = 500 μm (A, B, D), 1mm (C), 2 mm (E), 200 μm (F).

C4 plants of interest as they’re more efficient at photosynthesis than most plants, which are dubbed C3 as they first fix carbon into phosphoglyceric acid, a molecule with 3 carbon atoms. C4 plants have an extra step in photosynthesis, resulting in a reduced loss of water in photosynthesis. This ability to conserve water makes them of interest for crop development.

Further reading

Junqueira, N. E. G., Ortiz-Silva, B., Leal-Costa, M. V., Alves-Ferreira, M., Dickinson, H. G., Langdale, J. A., & Reinert, F. (2018). Anatomy and ultrastructure of embryonic leaves of the C4 species Setaria viridis. Annals of Botany, 121(6), 1163–1172. https://doi.org/10.1093/aob/mcx217