Genetic Control of Anther Cell Division and Differentiation 367
for restricting sporogenous cell number and promoting normal anther wall
formation in rice (Nonomura et al. 2003). A similar mutant,multiple arch-
esporial cells1(mac1), has been described in maize, where the cell lineage
in anther development is well defined (Sheridan et al. 1999) (Fig. 2). In the
Fig. 2 Cross-sections of maize wild-type andmac1mutant anthers.A–CWild-type;D–
Fmac1.AAstagecomparabletoArabidopsislate stage 4, the anther has the four cell
layers, and the inner secondary parietal layer is dividing to form the middle layer and
tapetum (small arrowheads).BAn anther with five distinct cell layers.CAstagecompa-
rable toArabidopsisearly stage 6, the PMCs are in prophase I of meiosis.DAstagesimilar
to that inA. Cell patterning is disrupted at this stage. The primary parietal layer has not
divided periclinally and the inner sporogenous cells appear to have proliferated abnor-
mally.EAstagesimilartothatinB,themac1mutant primary parietal layer continues
to persist, while the sporogenous cells have formed additional layers, the innermost of
whichhastheappearanceofPMCs.FA stage comparable to that inCin themac1mu-
tant anther, the inner cell layers are disrupted; the primary parietal cells persist in the
endothecial position, no tapetum is formed, and while the inner-most PMC-like cells have
entered prophase I of meiosis, they are irregularly shaped and are surrounded by a largely
disorganized array of unknown cell types. Ep, epidermis; PP, primary parietal; OSP, outer
secondary parietal; ISP, inner secondary parietal; S, sporogenous; En, endothecium; ML,
middle layer; T, tapetum; PMC, pollen mother cells; Mc, meiocyte; U, unknown cell type.
This figure was modified from Figs. 1 and 2 of Sheridan et al. (1999) with permission
from the Genetics Society of America