Co-localization of polysomes, cytoskeleton, and membranes with protein bodies from corn endosperm

Summary

Frozen corn endosperm was homogenized in a cytoskeleton-stabilizing buffer and stained directly (without pelleting) with rhodamine-phalloidin for actin and either thiazole orange to stain RNA or DiOC₆ to stain membranes prior to examination under the fluorescence microscope. Other samples were treated with a non-ionic detergent alone or in conjunction with a ionic detergent prior to staining and fluorescence microscopy. Very gentle homogenization in unsupplemented buffer yielded a massive aggregate containing protein bodies that fluoresced after treatment with the ER stain DiOC₆. This aggregate was capped by an aggregate of unstained starch grains. More vigorous homogenization yielded more disperse patterns showing almost identical co-localization of ER, actin and RNA (polysomes). Homogenization in buffer plus non-ionic detergent removed most of the membrane yet maintained co-localization of actin and polysomes, while homogenization in double detergent removed the last traces of membrane and actin, and released over 70% of the polysomes. We interpret these results to suggest that protein bodies are surrounded by membranes, cytoskeleton and RNA (polysomes) and that the majority of the polysomes are attached more firmly to the cytoskeleton than to the membrane. This provides evidence from fluorescence microscopy to supplement that from biochemical analyses for the existence of cytomatrix-bound polysomes in plants.