Leaf rolling allows quantification of mRNA abundance in mesophyll cells of sorghum

In the leaves of most C-4 plants, mesophyll (M) and bundle sheath (BS) cells develop and maintain highly differentiated biochemical networks. Separation and analysis of M and BS cells has greatly influenced our understanding of the C-4 pathway. A number of approaches including mechanical separation, digestion with cell wall-degrading cocktails, laser-capture microdissection, and leaf rolling have been used to isolate these cell types. Although leaf rolling is conceptually and practically the simplest method, to date it has only been used to assess the metabolite content of M cells from C-4 leaves of maize. This study reports an adapted leaf-rolling method for the isolation of high-quality RNA from M cells of sorghum. Analysis of leaf cell structure, RNA integrity, and transcript abundance of marker genes demonstrated that the sap collected by leaf rolling was from M cells and had no significant contamination. It was concluded that leaf rolling is a fast, cheap, and efficient method of measuring transcript abundance in M cells of sorghum.