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

Stamen = filament + anther

Angiosperms: Production of Male Gametophyte

Meiosis inside anther male spores

Details follow

Meiosis in lily anther 4 haploid daughter cells, also called “pollen tetrads”


HaploidHaploid

HaploidHaploid

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”.


HaploidHaploid

HaploidHaploid

Pollen tetrads = microspores

As anther matures, 4 microspores of a tetrad separate from each other


Haploid nucleus of each microspore undergoes a single mitotic division

Pollen Grain

Mitosis

Haploid

Haploid

HaploidHaploid

The 2 resulting haploid nuclei become encased in a thick, resistant wall, forming a pollen grain.

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.


Pollen Grain

Mitosis

Haploid

Haploid

HaploidHaploid

The pistil (female reproductive portion) is composed of the stigma, style, and ovary.

Angiosperms: Production of Female Gametophyte

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

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

Alternation of Generations: Angiosperms

Fertilization and Embryo Formation

Pollen grain landing on stigma of ovary

pollen tube growth

2 haploid cells of pollen grain are called the “generative cell” and the “tube cell”


Pollen tube growing from a pollen grain


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


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


Pollen tube continues to grow, entering ovule through opening called the “micropyle”


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”.


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.

Developing zygote, endosperm, and other tissues of the ovule eventually become a seed

Development of the Young Dicot Sporophyte

Corn

Bean

Example follows


developing ovules

ContinuedLongitudinal section through Capsella ovary


Suspensor

Continued

endosperm

Developing embryo proper


As the embryo develops, cotyledons begin to grow

As development continues, cotyledons fill entire embryo sac


Here is a longitudinal section of an ovary with a number of well-developed ovules inside.


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

Sclerenchyma

Fibers Sclereids

Collenchyma

Parenchyma

Common Plant Cell Types

Vessel elements & tracheids: important in xylem tissue

sieve tube members & companion cells: important in phloem tissue

cork cells: important in bark tissue

Primary vs. Secondary Growth

Secondary growth = growth in girth (width), e.g. Tilia stem cross-section

Primary growth= growth in length, e.g. in seed germination

Whether they are involved in primary or secondary growth, all plant cells and tissues arise from three primary meristems*:

• protoderm

• ground meristem

• procambium

Primary Meristems

*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

Vascular Cambium

Cork cambium cork

2o phloem

2o xylem

Periderm

Tissue Arrangement in Typical Herbaceous Stems

EpidermisCortexVascular bundle

Pith

Interfascicular cambium

Fascicular cambium

Phloem

Xylem

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

Vascular cambium

Secondary xylem

Primary xylem

Pith

Secondary phloem

Phloem ray

Cell Types in Secondary Phloem Ray of Bark

Fibers

Sieve tube members Companion cells

Simple versus Compound Leaves

Rachis

Pinnate

Generalized Leaf Anatomy

Typical Dicot Leaf X-Section

Palisade Parenchyma

Spongy Parenchyma

Vascular bundles

Epidermis

Cuticle

Stoma

Guard Cells

Typical Monocot Leaf X-Section

Xylem

Phloem

Bulliform Cells

Stoma

EpidermisMidvein Vein Bundle sheath cell

Leaf Stomata: Allow Gas Exchange

Stomata in Zebrina leaf epidermis

Guard cells with

chloroplasts

Stoma

Subsidiary cells

Bulliform Cells

Let’s see some TRICHOMES!

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

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