There has been a considerable gain in knowledge regarding the dynamics of ER morphology in fully differentiated plant cells through the use of vital fluorochromes and GFP technology in connection with the CLSM. GFP technology is best suited to studying ER biogenesis, ER morphology and its functional relationships, molecular aspects involved in ER organization changes during cell differentiation and plant organ development, or as a response to stress. GFP can be tagged to proteins located either in the lumen, the membrane, or closely associated with ER domains. To distinguish in living cells between ER domains involved in protein synthesis and others by fluorescence microscopy would be most desirable. Other questions will concern the possible association of the ER with other organelles such as mitochondria, vacuoles, and the PM, the role of AFs and MTs in ER organization in accordance with the cell cycle, and how Ca2+ or protons are involved in the regulation of ER morphology dynamics. Mutants such as the Arabidopsis "pilz" group genes (Mayer et al. 1999), which are indispensable for microtubule organization, might be useful for studies of the role of MTs in ER organization during mitosis and cytokinesis.
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