Morphology, anatomical terms, and staging of maize anthers. Morphology, anatomical terms, and staging of maize anthers. (A) Major structures of a maize plant relevant to understanding anther ontogeny. The final panel also indicates the X-, Y-, and Z-axis designations used in confocal microscopic analysis of anther cells. The Y-axis is the length dimension used as a proxy for anther developmental stage. Abaxial and adaxial lobes of the anther are indicated in the transverse view, as are the intermicrosporangial stripes (IMS) 1 and 2 that separate the lobes. A color code for the anther lobe cell types is provided at the bottom of the figure. (B) Complete timeline of maize anther development from organ identity specification through pollen shed. The dotted box outlines the period corresponding to (C). Descriptors are provided for the key events in anther development across the entire timeline. The microspore stages are abbreviated: archesporial cells (AR); meiocytes (ME); quartet stage of microspores (Q); uninucleate microspore (UM); binucleate microspore (BM); and mature pollen (MP). (C) Tracings of anther lobes in transverse section after anther staging by length with the typical number of days of development since anther primordium inception are also indicated. Given the variable environment of plant growth in the field and greenhouse, days are approximate, but anther lengths are tightly correlated with developmental stage. The gray bar provides a guide to the key developmental events and the span of each event. The graph depicts the increase in cell numbers from 0.2 mm to 1.6 mm (germinal cell specification through entry into meiosis). Not included in the graph are the vasculature and connective tissue cells in the center of each anther, which constitute ∼10% of all cells. Han Zhang et al. G3 2014;4:993-1010 ©2014 by Genetics Society of America