SUMMARY
In leaves of C4 plants the reactions of photosynthesis become restricted between two compartments. Typically, this allows accumulation of C4 acids in mesophyll cells to drive their diffusion into the bundle sheath. In C4 monocotyledonous grasses proliferation of plasmodesmata between these cell types is thought to increase cell-to-cell connectivity to allow efficient metabolite movement. However, it is not clear if C4 dicotyledons also show enhanced plasmodesmal connectivity between these cell types and whether this is a general requirement for C4 photosynthesis is not known. How mesophyll and bundle sheath cells in C4 leaves become highly connected is also not known.
We investigated these questions using 3D- and 2D-electron microscopy on the C4 dicotyledon Gynandropsis gynandra, and phylogenetically close C3 relatives.
The mesophyll-bundle sheath interface of C4 G. gynandra showed higher plasmodesmal frequency compared with closely related C3 species. Formation of these plasmodesmata was induced by light. Pharmacological agents that perturbed chloroplast development or photosynthesis reduced the number of plasmodesmata, but this inhibitory effect could be reversed by the provision of exogenous sucrose.
We conclude that the enhanced plasmodesmata formation between mesophyll and bundle sheath cells of C4 G. gynandra appears to be wired to the induction of C4 photosynthesis.
Competing Interest Statement
The authors have declared no competing interest.
