L. Zonia et al., Unique actin and microtubule arrays co-ordinate the differentiation of microspores to mature pollen in Nicotiana tabacum, J EXP BOT, 50(334), 1999, pp. 581-594
The complex cellular events that occur during development of the male gamet
ophyte of higher plants suggest a role for the cytoskeleton. This investiga
tion has revealed that unique microtubule arrays mediate events that occur
during microspore development; both actin and microtubule arrays have impor
tant roles during the asymmetrical microspore mitosis and unique actin arra
ys mediate events that occur during early pollen development, Migration of
the nucleus to the generative pole during cellular polarization of the micr
ospore is mediated by a microtubule cage that encloses the nucleus. Nuclear
position at the generative pole is maintained by an actin net that tethers
it to the pole prior to the asymmetrical mitosis. During entry into mitosi
s, the microtubule cage becomes modified and transforms into the asymmetric
al mitotic spindle, Actin is localized within the region of the mitotic spi
ndle and in the phragmoplast, following mitosis, actin networks enclose fir
st the generative cell and then the vegetative nucleus. These actin network
s function during migration of the generative cell and vegetative nucleus t
oward the centre of the pollen grain. Mature pollen contains a dense cortic
al actin meshwork and a disc-shaped microtubule array enclosing the generat
ive cell. The functional importance of the unique actin and microtubule arr
ays is verified by their targeted disruption with specific cytoskeletal inh
ibitors, which disrupt normal development and cellular morphology. In summa
ry, these data provide evidence that the co-ordinated reorganization of uni
que actin and microtubule arrays is an essential determinant of microspore
and pollen development.