Plasmodesmal connectivity in C₄Gynandropsis gynandrais induced by light and dependent on photosynthesis

In leaves of C₄plants the reactions of photosynthesis become restricted between two compartments. Typically, this allows accumulation of C₄acids in mesophyll cells and subsequent decarboxylation in the bundle sheath. In C₄grasses proliferation of plasmodesmata between these cell types is thought to increase cell-to-cell connectivity to allow efficient metabolite movement. However, it is not known if C₄dicotyledons also show this enhanced plasmodesmal connectivity and so whether this is a general requirement for C₄photosynthesis is not clear. How mesophyll and bundle sheath cells in C₄leaves become highly connected is also not known.

We investigated these questions using 3D- and 2D- electron microscopy on the C₄dicotyledonGynandropsis gynandraas well as phylogenetically close C₃relatives.

The mesophyll-bundle sheath interface of C₄G. gynandrashowed higher plasmodesmal frequency compared with closely related C₃species. 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 enhanced formation of plasmodesmata between mesophyll and bundle sheath cells is wired to the induction of photosynthesis in C₄G. gynandra.