Plant Physiology, Reproduction, and Systematics

Plant Response and Hormones

Plants have fascinating chemical control systems for development, growth, metabolism, and reproduction.

Plant Movement ­ Yes, plants move!

Phototropism - (tropism, greek "turn") Movement of Auxin to "light-side" of stems that stimulates tissue growth.

examples:

Gravitropism - movement of auxins to "lower" sides of roots caused by chemical attraction to Ca+ ions in specialized vessicles called "Statoliths"

examples:

can you think of an example from class of a leaf or stem that grows downward?

Thigmotropism (thigma, greek "touch")
Regulation connected to ethylene production and cuased when a mechanical stimulation occurs. (one side of a stem thins, and the other thickens to move or twist the plant in a certain direction)

Turgor Pressure - You have seen this in stomata. Also with rapid leaf movements and periodic ("sleep") movements due to potassium ion pumps.

ex's: Protection against predators, water loss, temperature fluctuation, or to capture food

Light - Induced Rhythms - Photoperiodism and flowering are regulated by a light - phytochrome hormone biofeedback

Short Day - Flowering stimuated by days less than (usually) 12 hours

Long Day - Flowering stimuated by days longer than 14 hours

Day Neutral - Flowering stimulated by plant maturity (and other factors such as temperature and moisture) rather than day length.

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Hormone ­ Any chemical produced by an organ that has a functional affect on remote cells.

Auxin ­ A plant hormone that causes growing tip elongation

ex. Indol Acetic Acid also synthetics like 24D

Anatomical Location
Embryo, Meristems, Apical Buds, Young leaves

Functions
Stem elongation
Root growth
Branching and cell differentiation
Fruit development
Phototropism and Gravitropism

Abscisic Acid ­ a plant hormone involved with seasonal/environmental control of growth.

Anatomical Location
Leaves, stems, immature fruits

Functions

Slows growth, closes stomata during water stress
Slows tissue growth
Maintains dormancy

Pherimones ­ These are special hormones that are released into the atmosphere and have their affect on the same or other individuals.

Ex. Ethylene (Pherimone)

Anatomical Location
Stem and leaf nodes, Leaves

Functions
Fruit Ripening
Involved with bio-feedback during Autumn to counter effects of auxins

Plant Reproduction and Development

Plants have reproductive systems that can be traced along an evolutionary line all the way back to ancient organisms evolving increased fitness by being diploid (or having some diploid stage in their life-cycle)

List some benefits to being Diploid:

Adaptive features for life on land

Division of Labor-Tissues and organs

Meiosis and Alternation of Generations

We know that diploid organisms produce sex cells called gametes as a product of meiosis.

In many life-forms, these become the gametes (Sperm and eggs).

In many other life-forms such as plants, these products of meiosis are spores. In simple protozoans or algae these cells can unite to re-establish the diploid condition and produce a zygote.

Plants have spores that germinate into distinct haploid life-forms and so, exhibit a reproductive strategy that has two distinct and separate growth forms, one haploid and one diploid

This is Alternation of Generations.

The part of the plant responsible for producing haploid spores by meiosis is called the Sporophyte (Spore making plant). When haploid spores germinate, they germinate into a gametophyte (gamete producing plant).

Draw a basic life cycle here:

We'll examine a series of plants in class.

* Know where meiosis occurs!
* Is water necessary for transfer of gametes?

In Vascular plants (Cone and Flower producing plants) The gametophyte is retained inside the sporophyte.

The female gametophyte remains in ovaries and the male gametophyte germinates from pollen spores inside female cone or on flower's stigma.

Synopsis of Plant Groups:

Nonvascular plants - Bryophytes. All homosporous (no distinctive differenc between male and female spores)

Very little or no tissue specialized for conducting water or food

Water is necessary for fertililization (sperm swims to egg)

Separate generations with the gametophyte dominant in most

examples of both aquatic and terrestrial mosses.

Seedless Vascular plants -

Psilophyta (whisk ferns [tropical with no true leaves]

Lycophyta > (Lycopodium [club moss with true leaves]
(Selaginella [club moss with true leaves *heterosporous]

Sphenophyta (Equisetum [horse tails with true leaves,
rhizomes, well developed vasular tissue)

Pterophyta (Ferns with highly developed leaves, vasular tissue, and roots/rhizomes)
*here either self fertilization occurs or their is physiological incompatibility or hormone suppression so separate male and female
gametophytes form.

Seed-producing Vascular plants

In Seed-producing, Vascular plants (Cone and Flower producing plants) The gametophyte is retained inside the sporophyte as either ovaries.

The pollen does not germinate into the gametophyte untill it lands on the proper surface (inside female cone or on flower's stigma).

Sporophyte is dominant

Gymnosperms: Seeds not enclosed by fruit. ("naked seed")
Includes Ginko biloba Link Here For Ginko Info. and Cycads where swimming sperm are still seen. . . although sperm utilize plant fluids, not outside environmental water. The more advanced Coniferophyta (pines, redwoods, firs, junipers, larch, cypress, hemlock) have wind pollination.

Angiosperms: Seeds surrounded by fruit. ("vessel seed")
Most advanced plants with wind, water, and animal pollination.
Douple fertilization - pollen germinates and has two sperm, one that fertilizes the egg and one that fertilizes other nuclei in the megagametophyte (female). These are the polar nuclei found surrounding the egg cell.




Special cases of angiosperms - Parasitic plants:

The local "Indian Pipe" Monotropa uniflora"

The South East Asian Rafflesia