Taken at face value that is a pretty daft question. After all, it is well known that chloroplasts are for photosynthesis. True, but what about the chloroplasts in the guard cells (GCCs) of stomata?

Chloroplasts in those highly specialised epidermal cells are quite far removed from those of mesophyll cells and presumably not involved in generation of photosynthate destined for export to sinks within the plant – an important role of those mesophyll-located organelles. So presumably any role of GCCs is local to their position in the guard cells, and is an area that has many questions and few answers. But work by Tamar Azoulay-Shemer et al. sheds some light on this topic.

Using transgenic arabidopsis plants – with chlorophyll-deficient guard cells – their data support the view that guard cell photosynthesis is critical for energization and guard cell turgor production (which leads to stomatal opening). So, hopefully, another piece of the complex jigsaw that is stomatal physiology and behaviour can be slotted into place.