Wednesday, February 17, 1999
Announcements:

Lecture notes: Test on Friday

1. Water entering the central vacuole at a higher rate, stretches the cell and forces it to keep adding to the cell wall. As cellulose and other support molecules are added, the cell wall becomes so rigid that it cannot grow any more. The pressure inside makes the cell very firm. This is called Turgor.
2. A lot of hormones.

Auxins: these cause elongation of stem cells and elongation of the coleptyle (the first shoot out of the seed)

Gibberellins: these cause stem elongation and help break dormancy of seeds and buds.

Cytokinins: increase cell division and retard leaf aging.

Abscisic acid: promotes closure of stomata, may trigger dormancy in leaves and seeds.

Ethylene: promotes fruit ripening and abscission (leaf drop)

*Florigan: proposed - promotes flowering

Reminder: Sporophyte: Diploid (2n) Spore producing body. (what we think of as the plant)

Gametophyte: Haploid (1n) Gamete producing body Male-pollen grains Female-embryo sacs in ovules.

Angiosperm gametophytes are in the flower.

"Perfect" flower: one with both male and female reproductive structures in the same flower.

"Imperfect" flower: one with one type of reproductive structure (male or female). Some plants have male and female
flowers on the same plant (oak trees). Some have male and female plants (holly, passion fruit, and
Kiwi vines).

Stamen: Anther- pollen sac
Filament- stalk

Carpel: Stigma- landing platform
Style- stalk
Ovary- contains ovules and accessory structures

Pollination: getting pollen to the stigma. (Plants use air currents, insects, birds, etc.)

Fertilization: egg meets sperm

1. Pollen grain lands on stigma
2. Sperm cell divides (2 nuclei)
3. Pollen tube cell makes pollen tube.
4. The sperm cell is carried along as the tube grows.
5. Double fertilization occurs.
   a. the 1^st sperm nucleus units with the egg to form a zygote.
   b. 2^nd sperm nucleus unites with the n+n "endosperm mother cell" to become the endosperm of the seed (nutrition for the embryo)
   c. Endosperm cells are triploid (3n). (the sperm contributes 1n, the endosperm mother cell contributes n+n = 3n)

The ovule becomes the seed.

The covering of the embryo sac becomes the seed coat.

The ovary becomes the fruit. Two types: dry-pea and fleshy-cherry.

New plants arise from:

Runner: nodes on and above ground horizontal stem (strawberries)

Rhizome: nodes on an underground horizontal stem (iris, ginger)

Corm: axillary bud on a short thick vertical underground stem (gladiiolus)

Tuber: axillary bud on underground rhizomes (potato eyes)

Bulb: axillary bud on a short underground stem (onion, tulip)

Parthenogenesis: embryo develops from an unfertilized egg (orange, rose)

Vegetative propagation: new growth from plant parts (jade plants, philodendron)

Tissue culture: lab technique