Electro-optical imaging of F-actin and endoplasmic reticulum in living andfixed plant cells

Confocal and video micrographs of living and fixed alfalfa roots, onion epi thelial and pear pollen cells illustrate the architecture of the cytoskelet on and endoplasmic reticulum in plant cells. Fixation of plant tissues to p reserve cytoplasmic structure poses special problems. When possible, emphas is should be placed on the imaging of structures in stained living cells ov er time. The early events that occur when Nod factors or bacteria elicit no dule formation in alfalfa roots will illustrate several approaches to plant cell fixation, staining and imaging. The first observable events after Nod factor stimulation occur in root hairs and are changes in rates of cytopla smic streaming, nuclear movements, and changes in the shape of the vacuole. Within ten minutes, the endoplasmic reticulum shifts position towards the tip of the root hair. For comparison, the endoplasmic reticulum localizatio n in pollen tubes and onion epithelial cells will be illustrated. The actin cytoskeleton undergoes a series of changes over a twelve hour period. Thes e changes in the cytoskeleton are spatially and temporally correlated with the observed growth changes of the root hairs. This dynamic change of the a ctin filament and endoplasmic reticulum and associated secretory vesicles i n these root hairs suggests a mechanism for the observed root hair growth c hanges.