A cortical cytoplasmic ring predicts the division plane in vacuolated cells of Coleus: the role of actomyosin and microtubules in the establishment and function of the division site.

•  The role of actomyosin and microtubules (MTs) in division plane establishment and cell plate expansion was studied in vacuolated cells of Coleus. •  Fluorescence and conventional microscopy were applied on control material and after treatment with anti-MT and anti-actin filament (AF) drugs as well as myosin inhibitors. •  The division plane is predicted by a cortical cytoplasmic ring (CCR), rich in AFs and endoplasmic reticulum, formed at interphase. The nucleus migrates to the CCR before its entrance in the phragmosome. The latter consists of transvacuolar cytoplasmic strands connecting the perinuclear cytoplasm with the CCR. During preprophase, a preprophase MT band is organized in the CCR. AF disruption and myosin inhibition destroy the CCR and cytoplasmic strands, arrest migration of the nucleus and affect cell plate expansion. MT disorganization inhibits anchoring of the cytoplasmic strands into the division plane. •  These observations support that CCR establishment, formation of transvacuolar cytoplasmic strands, migration of the nucleus and lateral cell plate expansion depend on actomyosin. The MTs guide and anchor the cytoplasmic strands of the phragmosome into the predetermined division plane.