Germline Development and Fertilization Mechanisms in Maize Liang-Zi Zhou, Martina Juranić, Thomas Dresselhaus  Molecular Plant  Volume 10, Issue 3, Pages 389-401 (March 2017) DOI: 10.1016/j.molp.2017.01.012 Copyright © 2017 The Authors Terms and Conditions

Figure 1 Gametophyte Development in Maize. (A) Male and female germlines are initiated from bisexual primordia of inflorescence meristems. (B–G) Female gametophyte development. (B) Megaspore mother cell at metaphase stage of meiosis I. (C) Linear tetrad: the two micropylar megaspores started to generate (arrowhead). (D) Functional megaspore at late FG1 stage: two separate vacuoles are visible (asterisks; arrowhead points toward remnants of degenerated megaspores). (E) Late FG2 stage: one nucleus (arrow) migrated toward the micropylar region. Remnants of degenerated megaspores are still visible (arrowheads). (F) FG5 stage: four nuclei are visible at the micropylar pole (arrow); the four nuclei at the chalzal pole are not in focus (asterisk). (G) FG7 stage showing the mature embryo sac with female gametes. Asterisk marks polar nuclei. Images (B) to (E) are modified after Juranić et al. (2012). (H–P) Pollen development. (H) Pollen mother cell. (I) Tetrad formation after meiosis. (J) Released microspore after callose dissolution. (K) Early unicellular stage with multiple small vacuoles. (L) Late unicellular stage with a large central vacuole. The porus (arrowhead) is already formed (not in focus). (M) Early bicellular stage after asymmetric cell division (pollen mitosis I): the generative cell (GC) is of similar size to the vegetative nucleus (arrow) of the tube cell. (N) The GC labeled with YFP-α-tubulin was transported to the opposite pole of the vegetative nucleus (arrow). (O) The GC during pollen mitosis II. The spindle apparatus is labeled in green. (P) Mature tricellular pollen containing two spindle-shaped sperm cells attached to each other (labeled by YFP-α-tubulin). AP, antipodals; CC, central cell; EC, egg cell; GC, generative cell; P, pistil primordia; S, stamen primordia. The porus is indicated by an arrowhead in (L), (M), (O), and (P). Scale bars represent 20 μm. Molecular Plant 2017 10, 389-401DOI: (10.1016/j.molp.2017.01.012) Copyright © 2017 The Authors Terms and Conditions

Figure 2 Progamic Phase and Fertilization Process in Maize. (A) Maize cob at silking stage. Husk leaves have been removed. Each silk fiber represents an elongated stigma attached to a single ovary. (B) Freshly pollinated maize silks. Numerous light-yellow pollen grains are adhered at papillae hairs of silk fibers. (C) A schematic model showing the journey of one pollen tube from a papillae hair through the transmitting tract of stigma and style toward the female gametophyte is shown in the middle. Propidium iodide staining pseudocolored in green shows two papillae hairs in the pink box at the top right. Blue box at top left shows toluidine blue staining of a germinating pollen tube invaded in a silk hair. Orange box shows cross-section through the silk showing a pollen tube (arrow) in the transmitting tract. Bottom left: schematic of a mature female gametophyte consisting of the cells indicated. A pollen tube containing the male germ unit (two sperm cells associated to the vegetative tube nucleus) in its tip is attracted by secreted ZmEA1 peptides. Pollen tube burst occurs through the activity of secreted ZmES4 and ZmPMEI proteins as illustrated in the box at bottom right. Molecular Plant 2017 10, 389-401DOI: (10.1016/j.molp.2017.01.012) Copyright © 2017 The Authors Terms and Conditions