A rapid and robust leaf ablation method to visualize bundle sheath cells and chloroplasts in C3 and C4 grasses

Abstract

Background: It has been proposed that engineering the C4 photosynthetic pathway into C3 crops could significantly increase yield. This goal requires an increase in the chloroplast compartment of bundle sheath cells in C3 species. To facilitate large-scale testing of candidate regulators of chloroplast development in the rice bundle sheath, a simple and robust method to phenotype this tissue in C3 species is required. Results: We established a leaf ablation method to accelerate phenotyping of rice bundle sheath cells. The bundle sheath cells and chloroplasts were visualized using light and confocal laser microscopy. Bundle sheath cell dimensions, chloroplast area and chloroplast number per cell were measured from the images obtained by confocal laser microscopy. Bundle sheath cell dimensions of maize were also measured and compared with rice. Our data show that bundle sheath width but not length significantly differed between C3 rice and C4 maize. Comparison of paradermal versus transverse bundle sheath cell width indicated that bundle sheath cells were intact after leaf ablation. Moreover, comparisons of planar chloroplast areas and chloroplast numbers per bundle sheath cell between wild-type and transgenic rice lines expressing the maize GOLDEN-2 (ZmG2) showed that the leaf ablation method allowed differences in chloroplast parameters to be detected. Conclusions: Leaf ablation is a simple approach to accessing bundle sheath cell files in C3 species. We show that this method is suitable for obtaining parameters associated with bundle sheath cell size, chloroplast area and chloroplast number per cell.