CHAPTER 11
PLANT EMBRYOLOGY
REVIEW QUESTIONS
ANTHER AND POLLEN DEVELOPMENT
1. What are the two major anther types and how do they differ?
a) dithecal or tetrasporangiate-anthers with 2 thecae, each with 2 microsporangia.
b) monothecal or bisporangiate-anthers with 1 theca, with 2 microsporangia.
2. What criteria are used to define the four types of anther wall development?
Based on the total number of wall layers and their developmental origin.
3. What is the tapetum? What are the two types of tapetum development and how do they differ?
a) The tapetum is the innermost cell layer of the anther, consisting of metabolically active cells that function in the development of pollen grains.
b) Secretory (glandular), in which the tapetal cells remain intact. Amoeboid (plasmodial or periplasmodial), in which the tapetal cell walls break down, with release of the cytoplasm of the tapetal cells into the locule.
4. What are two types of anther endothecial anatomy?
Based on the structure of the secondary wall thickenings: girdling, in which the secondary wall thickenings form rings with cross bridges between them, and spiral, in which the secondary wall thickenings are spiral or helical in shape.
5. What is microsporogenesis and what are the two major types?
Microsporogenesis is development of microspores from microsporocytes.
The two types are:
a) Successive, if cytokinesis occurs after meiosis I;
b) Simultaneous, if cytokinesis doesn’t occur until after meiosis II.
6. What is microgametogenesis and what are the two major types?
Microgametogenesis is development of pollen grains (male gametophytes) from microspores, technically beginning with the first mitotic division of the single microspore nucleus.
The two types are based on the number of nuclei present in the pollen grain at the time of anthesis, or flower maturation:
a) binucleate, containing one tube cell/nucleus and onegenerative cell/nucleus. The generative cell divides to formtwo sperm cells only after pollen tube formation.
b) trinucleate, in which the generative cell divides prior to pollen release.
OVULE DEVELOPMENT
7. Name the parts of a typical ovule.
Funiculus, megasporangium (nucellus), integument(s), micropyle, female gametophyte.
8. What is meant by the chalazal region? a raphe?
a) The region opposite the micropyle.
b) A region where the funiculus is adnate (or decurrent) to the nucellus, sometimes visible as a ridge in a mature seed.
9. Name and distinguish between the three types of nucellus. Which two resemble one another at maturity?
a) crassinucellate, composed of two (sometimes more by additional divisions) layers of cells, the inner derived from the parietal cell; tenuinucellate, composed on a single layer, derived from the original outer layer of the megasporangium; pseudocrassinucellate, in which no parietal cell is formed, yet periclinal divisions occur in the single outer layer, forming an additional inner layer of nucellar cells.
10. Name and distinguish between the three types of megasporogenesis.
Monosporic, in which meiosis is followed by cytokinesis, resulting in four megaspore
Cells, only one of which contributes to the female gametophyte.
Bisporic, in which cytokinesis occurs after the first meiotic division, but not the second, resulting in two cells, each of which contain two haploid nuclei, one of which contributes to the female gametophyte.
Tetrasporic, in which cytokinesis does not occur at all after meiosis, resulting in a single cell with four haploid nuclei, all of which contribute to the female gametophyte.
11. What criteria are used to distinguish between the numerous female gametophyte development types?
The particular type of megagametogenesis (the development of the female gametophyte from the haploid product(s) of meiosis), which is a function of mitotic divisions, the formation of new cells, and the fusion of existing nuclei or cells.
12. Which female gametophyte type is most common and probably ancestral in the angiosperms?
The Polygonum type, although a recent theory suggests that the 4-nucleate Nuphar/Schisandra type may be ancestral.
13. What are the two major integument types?
Bitegmic-2 integuments.
Unitegmic-1 integument.
14. What are the differences between endostomal, exostomal, amphistomal, unistomal, and zig-zag micropylar types?
Endostomal-if the micropyle is delimited by only the inner integument (the outer one being foreshortened).
Exostomal-if the micropyle is delimited by only the outer integument (the inner one being foreshortened).
Amphistomal-if the micropyle is delimited by both integuments.
Unistomal-if there is only one integument.
Zig-zag-if the micropylar pore of the outer integument is spatially displaced relative to the inner integument.
15. What criteria are used to distinguish between ovule types? Which type is most common and ancestral in the angiosperms?
a) Ovule types are defined primarily on the curvature of the funiculus and nucellus/female gametophyte, but also vasculature in some types.
b) The most common is the anatropous type.
16. Define and give three examples of ovule position.
a) Ovule position refers to the placement of the micropyle and raphe relative to the distal end (apex), proximal end (base), or sides of the floral axis.
b) Three types are: epitropous ovule, in which the micropyle points distally; hypotropous ovule, in which the micropyle points proximally; and pleurotropous, in which the micropyle points to the side.
SEED DEVELOPMENT
17. What is embryogeny and on what criteria are different embryogeny types based?
Embryogeny refers to the development of the embryo within the seed.
The sequence of divisions of the zygote can define various embryogeny types, which have been named after the major taxonomic groups where they occur.
18. What is ptyxis and what does it define?
Ptyxis refers to the aestivation of the cotyledons.
19. Name the three basic types of endosperm development and describe how they differ.
Cellular endosperm, in which the endosperm cell divides mitotically, regularly followed by cytokinesis. Thus, each endosperm nucleus is contained within a cell wall from the beginning.
Nuclear endosperm, in which the early mitotic divisions are not followed by cytokinesis. Thus, numerous nuclei are contained within a single cell, at least early in development; later, cell walls
Typically surround the nuclei.
Helobial endosperm, in which the first mitotic division is followed by cytokinesis, delimiting two cells.
20. Other than endosperm, what two other seed storage tissue origins occur in angiosperms?
Cotylespermous, in which the cotyledons enlarge and assume the function of storage tissue.
Perispermous, in which the chalazalnucellar cells enlarge and store energy-rich compounds.
21. Name four seed storage tissue origin types. Of what three major chemicals are seed storage tissues composed?
Endospermous or albuminous, in which the storage tissue is endosperm.
Exalbuminous, in which double fertilization and endosperm development occur, but the endosperm soon stops growing.
Cotylespermous, in which the cotyledons enlarge and assume the function of storage tissue.
Perispermous, in which the chalazalnucellar cells enlarge and store energy-rich compounds.
Composed of starch, oil, or protein.
22. What are arils and caruncles, and what is their function?
Aril-a fleshy seed layer that envelops the seed coat.
Caruncle or strophiole-a fleshy layer that doesn’t surround the seed coat, but forms as a basal appendage, typically near the hilum (the scar of the funiculus).
Both function as a food reward in animal dispersal.
EMBRYOLOGY AND SYSTEMATICS
23. Name some features of embryology that may be valuable in plant systematics.
Ovule type
Micropyle type
Nucellus type
Embryogeny
Female gametophyte (embryo sac) type
Obturator presence/absence
Seed storage tissue origin
Embryo type
Seed coat anatomy