H. Nguyen et al., Patterns of cytoskeletal organization reflect distinct developmental domains in endosperm of Coronopus didymus (Brassicaceae), INT J PL SC, 162(1), 2001, pp. 1-14
New data on the interrelationships of F-actin and microtubules during endos
perm development reveal distinct domains in the micropylar chamber (MC) con
taining the embryo, the large curved central chamber (CC), and the small ch
alazal chamber (ChC). Reported for the first time in any endosperm are the
following: (1) data on the interrelationships between microtubules and F-ac
tin during development in all three chambers, and (2) an early stage of syn
cytial endosperm characterized by unusual fusiform to multangular nuclei sh
eathed by parallel arrays of microtubules. As is characteristic of nuclear
endosperm development, the common cytoplasm is organized into nuclear cytop
lasmic domains (NCDs) defined by radial microtubule systems, which determin
e placement of walls at the cellularization stage. Both microtubules and F-
actin are reorganized in preparation of the syncytium for simultaneous cyto
kinesis. Cellularization directly follows formation of adventitious phragmo
plasts in the MC but is delayed in the CC as polarized NCDs elongate and an
ticlinal walls grow centripetally, thus forming a layer of open-ended alveo
li overtopped by the advancing front of syncytial cytoplasm containing the
adventitious phragmoplasts. Periclinal divisions in the alveoli cut off the
first layer of true cells and displace the alveoli inward. Repeated cycles
of alveolation and periclinal division complete initial cellularization of
endosperm in the CC. The ChC becomes occupied early on by a multinucleate
cyst of cytoplasm that fails to organize NCDs and that never cellularizes o
r that cellularizes irregularly very late in seed development but remains d
istinct from the remainder of the endosperm. Comparison of Arabidopsis thal
iana and Coronopus didymus shows endosperm development to be a highly conse
rvative process in mustard seeds.