The Effect of Hyperosmotic Stress on the Network Morphology and Transport Function of the Endoplasmic Reticulum in Tobacco

Abstract

To study the effect of hyperosmolarity on the dynamic morphology of the endoplasmic reticulum (ER) form change, Nicotiana benthamiana seedlings with ER-labeled GFP-HDEL were put in a culture chamber and gradually infused with high D-sorbitol concentrations. The ER was observed by time lapsed confocal microscopy. Under high osmotic stress, the dense reticulated network morphology of the ER reduced to a web or thread-like sparse connections. Further observational changes were decreased ER activity and increased cisternal ER domains. ER Recovery after replacing the culture chamber with MES buffer was rapid. FRAP analysis revealed that ER recovery after photobleaching in cisternae was more rapid than recovery in tubules. In addition, flow of molecules within ER post-treatment with high osmotic concentration was diffusional rather than directional. These results are consistent with many of the physiological stress response mechanisms that have been investigated.