Granum revisited. A three-dimensional model--where things fall into place.

The complex structure of higher plant chloroplasts has fascinated researchers for many years. Although the spatial relationship between granum and stroma thylakoids has been known for more than 20 years, most textbooks and research papers continue to include erroneous 3D models and simplified schemes. Here we present a simple computer model, based on electron micrographs from serial section of granum-stroma assemblies, showing the striking 3D structure of the stroma membrane wound around the granum. This model also provides an insight into some previously unknown functions of this intriguing multilamellar membrane system. However, many areas, such as self-assembly, structural flexibility and evolutionary niche, still remain to be explored.