, Volume 157, Issue 1-3, pp 92-101

Actin filaments line up acrossTradescantia epidermal cells, anticipating wound-induced divison planes

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This paper describes the role of actin filaments in setting up the phragmosome — the transvacuolar device that anticipates the division plane — and in forming a supracellular system that seems to override cell boundaries.

Tradescantia leaf epidermal cells were induced to divide by wounding the leaf. New division planes formed parallel to slits, and encircled puncture wounds — the new division planes lining up across cells, instead of the joints being off-set as in normal, unwounded tissue. Within 30 min after wounding, rhodamine phalloidin staining showed that a belt of fine, cortical actin filaments formed parallel to the wound. In the next stage, migration of nuclei to a wall adjacent to the wound, involved pronounced association of actin filaments with the nucleus. Migration could be inhibited with cytochalasin D, confirming the role of actin in traumatotaxis. Later still, actin strands were seen to line up from cell to cell, parallel to the wound, anticipating the future division plane. Next, actin filaments accumulated in this anticlinal plane, throughout the depth of the cell, thereby contributing to the formation of the phragmosome. The phragmosome has been shown in previous work (Flanders et al. 1990) to contain microtubules that bridge nucleus to cortex, and is now found to contain actin filaments. Actin filaments are therefore involved in the key stages of nuclear migration and division plane alignment. The supracellular basis of actin alignment is discussed.

Dedicated to the memory of Professor Oswald Kiermayer