Biological Foundations 112, Lecture 15

Pollen Development

Chapter 27, pages 566-567
Chapter 34, pages 731-732
Basic Botany-5 15:23-20:45

I.   Pollen Development

     A.   Meristem produces the filament and anther of the stamen

            1.   The anther has four pollen sacs with connective tissue that holds these four sacs
                  together into an anther

            2.   Each of the four anther sacs produces cells that differentiate into pollen grains

            3.   Each cell in each of the four pollen sacs differentiates into four pollen grains

     B.   Process of pollen grain formation

            1.   The cells within the pollen sacs are microspore mother cells (microsporocyte)

            2.   Each microspore mother cell is diploid

            3.   Each microspore mother cell divides by meiosis to produces four microspores

                  a.   This cluster of four microspores is called a tetrad of tetraspores

                  b.   Each microspore in the tetrad is haploid

            4.   Each microspore divides once by mitosis to form either a 2-celled microspore or a  
                  binucleated microspore depending upon the species of plant

            5.   Each microspore differentiates into a pollen grain by developing a heavy thick and  
                  sculptured wall around itself.

     C.   Pollen grain structure

            1.   Two nuclei occur in each pollen grain:

                  a.   One is the tube nucleus (or cell)

                  b.   One is the generative nucleus (or cell)

            2.   Heavy, thick cell wall with sculpturing of the cell wall

     D.   Fertilization

            1.   Pollen grain germinates on the stigma of the carpel

            2.   The tube nucleus directs the formation and extension of the liquefied pollen tube that
                  grows down the style to the ovule.

            3.   The generative nucleus divides by mitosis to form two sperm nuclei that migrate  
                  down the pollen tube together.

            4.   The sperm cells enter the ovule through the micropyle.

            5.   One sperm nucleus unites with the egg nucleus and the other unites with the
                  binucleated polar nucleus

            6.   Thus, immediately after fertilization:

                  a.   The polar nuclei fuse with one of the two sperm nuclei to form a triploid  
                        primary endosperm nucleus

                  b.   The egg nucleus and the sperm nucleus fuse to form a diploid zygote

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