REPRODUCTIVE BIOLOGY OF A FLOWERING PLANT
The following web page represents a copy of my notes that formed the basis of lectures given during the first portion of the Biology of Plants (BOT 1103) lecture course. Please refer to your own notes, handouts, and to the textbook (Stern, K., R., J. E. Bidlack, and S. H. Jansky. 2008. Introductory Plant Biology, McGraw-Hill. 616 pp. - reading assignments are in the syllabus) for additional information. This web page does not include information found in various handouts and related materials (e.g., films, charts, overhead projections, etc.) that you will receive during the course of the semester. You will be evaluated over this information as well. If you note any errors in the following document, I'd appreciate it if you would bring this to my attention. Email address: email@example.com.
Sexual Reproduction in Flowering Plants
Terms and concepts:
Evolutionary trends from haploid to diploid dominance:
In lower plants, the sporophyte is dependent on the gametophyte for nutrition (e.g., mosses, liverworts). For higher plants this trend is reversed (e.g., conifers, flowering plants). The female gametophyte is dependent on the sporophyte for nutrition. The male gametophyte (i.e., pollen) is independent for a brief period, but requires sporophyte tissue (i.e., the stigma and style) in order to grow, release, and disseminate sperm nuclei to the egg found in the female gametophyte. The following discussion emphasizes the process as it occurs in flowering plants.
Reproduction in Flowering Plants
Refer to your
textbook (see assigned readings in syllabus), class notes, and to the links listed below and know the definition to terms discussed
in class (e.g., incomplete vs. complete flower, imperfect vs. perfect flower, zygomorphic vs. actinomorphic flower, superior ovary vs. an inferior ovary,
pistil and parts, stamens and parts, corolla, calyx, adroecium, gynoecium,
If you are so inclined, you might consider visiting the web site for "Science Matters", which contains a 30 minute program on the Genetic Basis of Flowering (why some portions of the floral bud turn into sepals instead of stamens and so on). It is quite good. This program called Science Matters: The ABCs of Flower Development was shown in class on March 14th during the Biology of Plants lecture. The web address is: http://video.google.com/videoplay?docid=-3408394683405809314&q=flower. The original Web Site for this video is http://www.ucsd.tv/sciencematters/. I noticed that the program offers audio in English and Spanish, and subtitles in English or Spanish. If the lecturer starts speaking Spanish during the internet feed that you get and you don't happen to understand Spanish then click on the button that says “English audio.” This ought to transition it back to English in mid-sentence.
MEIOSIS AND SPOROGENESIS IN FLOWERING PLANTS
General Overview of Meiosis
1. Diploid cell (2n) containing 2 sets of chromosomes gives rise to haploid nuclei (1n) containing one set of chromosomes. Meiosis is a reduction division that occurs during the production of a spore ===> which gives rise to a haploid gametophyte (the gamete-producing plant) ===> which gives rise to the gamete (i.e., an egg or sperm).
2. Meiosis is divided into two parts: meiosis I (pairing of homologous chromosomes, crossing-over, and separation of homologues to separate cells); meiosis II (separation of non-identical sister chromatids into sister chromatids which go to separate poles of a dividing cell). In plants these haploid cells become the spore.
Terminology and figures for understanding meiosis
2 Divisions occur in Meiosis (Meiosis I and Meiosis II)
Genetic recombination through crossing-over.
MICROSPOROGENESIS - Diploid cell = microspore mother cell ==> meiosis ==> 4 spores at the end of process (i.e., tetrad). Each microspore becomes the pollen grain = male gametophyte.
MEGASPOROGENESIS - Diploid cell = megaspore mother cell ===> meiosis ===> 4 haploid megaspores ===> 3 degenerate leaving one big megaspore. Embryo sac = female gametophyte. Embryo sac + integuments (protective coverings, which develop into the seed coat) = ovule.
Pollination (i.e., deposition of pollen on the stigma of the pistil) may lead to pollen germination and eventual delivery of sperm nuclei to the embryo sac via a pollen tube. The pollen tube grows through the style of the pistil until it reaches the entrance of the embryo sac in the ovary.
POLLINATION AND FERTILIZATION ARE NOT EQUIVALENT TERMS
Pollination may be accomplished a
number of ways, but in flowering plants it usually involves dispersal by
wind or by a pollinator (e.g., bird, mammal, insect, lizard, etc.).
Double fertilization as it occurs in most flowering plants (about 70 %) Polygonum-type:
In lilies (process is atypical): megasporogenesis ==> all four megaspores form the embryo sac. Consequently during double fertilization the following happens:
Fruits types and seeds
VISIT http://botit.botany.wisc.edu/images/130/ FOR IMAGES OF PLANT CELLS AND TISSUES: CLICK ONTO LINKS LISTED AS ANGIOSPERM, MEIOSIS, FRUIT, AND EARLY DEVELOPMENT.
This web page was assembled by Dr. Martin J. Huss - Last modified on October 11, 2007.