The cytoskeleton in plant cell growth: lessons from root hairs.

In this review, we compare expansion of intercalary growing cells, in which growth takes place over a large surface, and root hairs, where expansion occurs at the tip only. Research that pinpoints the role of the cytoskeleton and the cytoplasmic free calcium in both root hairs and intercalary growing cells is reviewed. From the results of that research, we suggest experiments to be carried out on intercalary growing cells to test our hypotheses on plant cell expansion. Our main hypothesis is that instability of the cortical actin cytoskeleton determines the location where expansion takes place and the amount of expansion. Contents Summary 409 I. How do plant cells expand their surface? 409 II. Immunolocalization of epitopes in fixed root hairs for light-microscopy 410 III. The cytoskeleton in growing root hairs 412 1. Microtubules 412 2. Actin filaments 413 3. Free cytoplasmic calcium concentration 413 IV. The role of cytoskeletal elements and cytoplasmic free alcium in intercalary expanding root cells 414 1. Microtubules 414 2. Actin filaments 415 3. Free cytoplasmic calcium concentration 416 Acknowledgements 416 References 416.