Angiosperms: Production of Male Gametophyte Stamen = filament + anther Meiosis inside anther male spores Details follow

Angiosperms: Production of Male Gametophyte Meiosis in lily anther 4 haploid daughter cells, also called “pollen tetrads” Haploid

Angiosperms: Production of Male Gametophyte From the point of view of the plant life cycle, anther = male sporangium Each of the 4 pollen tetrads = spore Because of their small size, they are called “microspores”. Haploid Pollen tetrads = microspores

Angiosperms: Production of Male Gametophyte Haploid As anther matures, 4 microspores of a tetrad separate from each other Haploid nucleus of each microspore undergoes a single mitotic division Mitosis The 2 resulting haploid nuclei become encased in a thick, resistant wall, forming a pollen grain. Pollen Grain

Angiosperms: Production of Male Gametophyte Haploid From the point of view of the angiosperm life cycle, a pollen grain is an immature male gametophyte, since it has been produced by the mitotic division of a spore. Mitosis Pollen Grain

Angiosperms: Production of Female Gametophyte The pistil (female reproductive portion) is composed of the stigma, style, and ovary.

Angiosperms: Production of Female Gametophyte An ovary may contain a number of ovules. Meiosis takes place inside the ovules, resulting in the production of female spores. Details follow

Angiosperms: Female Gametophyte Only one of the haploid spores resulting from meiosis in the ovule matures. It undergoes 2 rounds of mitosis to form the “embryo sac”, which has 8 haploid nuclei. Embryo sac = female gametophyte

Alternation of Generations: Angiosperms To complete the life cycle, the gametes produced by the male and female gametophyte must unite, restoring the diploid sporophyte. Female gametophyte = embryo sac Immature male gametophyte = pollen grain

Fertilization and Embryo Formation Pollen grain landing on stigma of ovary pollen tube growth

Fertilization and Embryo Formation 2 haploid cells of pollen grain are called the “generative cell” and the “tube cell” Pollen tube growing from a pollen grain

Fertilization and Embryo Formation As pollen tube grows towards ovule, nucleus of “generative cell” divides by mitosis, producing 2 haploid sperm

Fertilization and Embryo Formation The pollen grain, along with the pollen tube containing 2 sperm, is the mature male gametophyte.

Fertilization and Embryo Formation Pollen tube continues to grow, entering ovule through opening called the “micropyle”

Fertilization and Embryo Formation One of the sperm fertilizes the egg, producing a diploid zygote. This zygote will divide and differentiate, forming the sporophyte plant. The angiosperm life cycle has been completed. The other sperm will fuse with the 2 central haploid nuclei in the embryo sac, producing a triploid nucleus. These events are called “double fertilization”.

Fertilization and Embryo Formation Tissue that develops from the triploid nucleus = “endosperm”. Energy stored in this tissue nourishes the developing embryo.

We have derived many medical compounds from the unique secondary compounds of plants. More than 25% of prescription drugs are extracted from plants, and many more medicinal compounds were first discovered in plants and then synthesized artificially.

Evolutionary Trends in Plant Life Cycles Angiosperms demonstrate an evolutionary trend in which the gametophyte is further reduced in size, and increasingly dependent upon the sporophyte.

Development of the Young Dicot Sporophyte Developing zygote, endosperm, and other tissues of the ovule eventually become a seed Bean Corn Example follows

Development of the Young Dicot Sporophyte developing ovules Continued Longitudinal section through Capsella ovary

Development of the Young Dicot Sporophyte Developing embryo proper Suspensor Developing embryo proper endosperm Continued

Development of the Young Dicot Sporophyte As development continues, cotyledons fill entire embryo sac As the embryo develops, cotyledons begin to grow

Development of the Young Dicot Sporophyte Here is a longitudinal section of an ovary with a number of well-developed ovules inside.

Development of the Young Dicot Sporophyte Today’s lab: examine external and internal structure of a mature ovule, i.e. a seed:

Seed Germination Germination and seedling development in beans

Common Plant Cell Types Collenchyma Sclerenchyma Fibers Sclereids Parenchyma

Common Plant Cell Types Vessel elements & tracheids: important in xylem tissue cork cells: important in bark tissue sieve tube members & companion cells: important in phloem tissue

Primary vs. Secondary Growth Primary growth= growth in length, e.g. in seed germination Secondary growth = growth in girth (width), e.g. Tilia stem cross-section

• protoderm • ground meristem • procambium Primary Meristems Whether they are involved in primary or secondary growth, all plant cells and tissues arise from three primary meristems*: • protoderm • ground meristem • procambium *Meristem: plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth

Primary & Secondary Growth in a Woody Stem Primary meristems Protoderm Ground meristem Procambium Primary Tissues Epidermis Pith Ground Cortex Primary phloem Primary xylem Lateral Meristem Secondary Tissues Periderm Cork cambium cork 2o phloem 2o xylem Vascular Cambium

Tissue Arrangement in Typical Herbaceous Stems Epidermis Cortex Vascular bundle Phloem Xylem Fascicular cambium Interfascicular cambium Pith Monocot Dicot

Secondary Growth in a Woody Dicot vascular cambium produces 2o xylem (= wood) to the inside, 2o phloem to the outside

Tilia cross-section Primary xylem Vascular cambium Secondary phloem Secondary xylem Phloem ray Pith

Cell Types in Secondary Phloem Ray of Bark Sieve tube members Companion cells Fibers

Simple versus Compound Leaves Rachis Pinnate

Generalized Leaf Anatomy

Typical Dicot Leaf X-Section Cuticle Epidermis Palisade Parenchyma Vascular bundles Guard Cells Spongy Parenchyma Stoma

Typical Monocot Leaf X-Section Bundle sheath cell Midvein Vein Epidermis Phloem Xylem Stoma Bulliform Cells

Guard cells with chloroplasts Leaf Stomata: Allow Gas Exchange Guard cells with chloroplasts Stomata in Zebrina leaf epidermis Stoma Subsidiary cells

Bulliform Cells

Let’s see some TRICHOMES!