Vascular plants lab - 8

Gymnosperm life cycle - first spring (microsporangiate cones)

• microsporocytes do meiosis in spring to produce microspores

• Some mitosis occurs immediately to produce the mature microgametophyte with three cells (i.e. pollen grain).

• Pollen is released and is transferred to the ovulate cones (usually a
  different tree) by wind

Gymnosperm life cycle - first spring (megasporocyte cones)

• pollen grains settle onto ovulate scales and adhere to 'pollination drops' that
  exude from the micropyle canals at the open end of the ovules

• The drops contract and draw in the pollen grain into contact with the nucellus

• The ovulate cone is now pollenated, and the scales grow together to protect the developing ovules

• four megaspores are produced by each megasporocyte; only one eventually
  develops into the megagametophyte while the other three degrade

• pollen grains begin to germinate and slowly starts to form a pollen tube

gymnosperm life cycle - first fall

• megagametophyte begins to develop by mitosis without cytokinesis and cell wall division and overwinters

• Thus, the megagametophyte doesn’t even bother to start developing until
  after pollination

gymnosperm life cycle - second spring

• megagametophyte is now a blob of approx. 2000 free nuclei (free-nuclear stage)

• Now it begins to make cell walls

• the pollen tube is still growing into the developing megagametophyte, and
  the generative cell divides to make a sterile cell and a spermatogenous cell,
  the latter of which divides again to produce two sperm

gymnosperm life cycle - second summer

• the megagametophyte has now produced archegona with egg cells

• the pollen tube reaches the eggs and discharges the sperm

• one sperm fertilizes the egg to produce a new 2n zygote and the other degenerates (pollination and fertilization occur 15ish months apart)

• Zygote continues to do mitosis and form the 2n embryo

• The integuments start developing into the seed coat

• The remaining gametophyte is full of lipids, which are used to support the
  growth of the new sporophyte when it sprouts

gymnosperm life cycle - second fall or third spring

The ovulate scales open and release the now fully-developed seed

how many cells in a mature microgametophyte (angiosperms)

2-3 nuclei

how many cells in a mature megagametophyte (angiosperms)

approximately 7 cells

do angiosperms have antheridia or archegonia

no

indirect pollination in angiosperms

• the pollen grains are deposited on the stigma

• after which the pollen tube conveys two non-motile sperm nuclei to the female gametophyte

what happens to the ovule and ovary after fertilization

• the ovule, which is enclosed in the ovary, develops into a seed

• the ovary develops into the fruit

microgametophyte (pollen) development

• diploid microsporocyte divides by meiosis to produce 4 haploid microspores

• each microspore divides by mitosis to produce a vegetative cell and a generative cell

• a second division occurs in the generative cells to produce two sperm cells in the vegetative cell

megagametophyte development

• megasporocyte (megaspore mother cell) undergoes meiosis to make 4 megaspores (three will degenerate)

• The haploid functional megaspore does three rounds of mitosis without cytokinesis to produce eight haploid nuclei

• The nuclei then migrate and produce different cell types: an egg cell, two synergid cells, three antipodal cells, and two central nuclei remain in the original mother cell cytoplasm (all together this structure is the embryo sack)

list the different cell types in the embryo sac

• egg cell

• 2 synergid cells

• three antipodal cells

• two polar nuclei (one cell)

what cells in the embryo sac are closest to the micropyle

the egg cell and 2 synergid cells

fertilization in angiosperms

• The pollen grain lands on the stigma and the pollen tube from the tube cell (vegetative cell) grows through the style, following ‘transmission tracts’

• Once it gets to the ovary, the pollen tube finds the micropile by following chemical cues put out by the antipodal cells in the embryo sac

• grows through micropile

• the generative cell divides to produce two sperm, one of the sperm fertilizes the egg to form a zygote

double fertilization

• The other sperm fertilizes the central cell with the polar nuclei to form a triploid (3n) endosperm tissue

• This tissue fills up with nutrients as the seed develops, which is eventually used to feed the growing seedling once it germinates

• only in angiosperms

the zygote develops into…

the embryo

integuments

outer coverings of the ovule that develop into the seed coat

the ovary wall forms…

the fruit

the ovule becomes…

the seed

what type of division occurs after fertilization

the diploid zygote divides through mitosis

what is produced from the first divisions of the zygote

• basal cell

• terminal cell

basal cell

divides transversely

terminal cell

divides longitudinally

what results from the division of the basal and terminal cells

a four celled proembryo

how does the suspensor develop

The suspensor develops from the lower cells in the pro-embryo via a series of transverse cell division

dermatogen cells and inner cells

• the young embryo consists of external dermatogen cells and eight
  internal cells from which the ground meristem and procambial cells will
  originate

hypophysis

• The suspensor cell on which the embryo rests

• Through a series of cell divisions, the hypophysis will form eight cells (two tiers of four cells)

• The tier closest to the suspensor will form the root cap while the tier closest to the embryo will differentiate into the radicle

3 layers of the ovary wall (fruit)

• exocarp: outer layer, often called the skin

• mesocarp: middle layer, often is fleshy

• endocarp: inner layer, modified in many ways

simple fruits

one flower and one ovary

aggregate

• single flower with many ovaries (multiple separate pistils)

• ex: strawberries, magnolia, raspberries, blackberries

multiple fruits

• fused ovaries of several fruits

• a bunch of separate flowers on an inflorescence get fertilized and all their fruits grow together into one mass

• ex: pineapples and figs

accessory fruits

ovary plus other floral tissues

examples of dry fruits

• maple tree seeds

• dandelions

• acorns

• nuts

examples of fleshy fruits

• peach

• cherry

• cucumber

• apple

dry fruit types

• achene

• samara

• nuts

• capsule

• legume

• follicle

• silique

• caryopsis

achene fruits

• dry and one seeded fruit

• lacks special seams that split to release the seed = indehiscent

• pericarp is dry and close to seed coat but not completely attached

• ex: sunflower seed and dandelions

samara fruits

• dry fruit

• the entire pericarp is thin and papery and surrounds the seed (helps with wind dispersal)

• technically just an achene with a papery pericarp

• ex: maple seeds

nuts

• dry fruit

• indehiscent (doesn’t have seams that split open)

• hard dry pericarp not attached to the seed coat

• essentially a big achene with a much thicker pericarp

• ex: acorns

capsule fruits

• dry fruits

• pericarp is dry and tough

• splits open along seams to release seeds (dehisces)

• Usually the ovary that made a capsule is compound with multiple carpels and
  multiple ovules in each carpel (lots of seeds)

• ex: poppies

legume fruit

• dry fruit

• unilocular with multiple seeds

• pericarp splits along two seams 

• ex: beans and peanut

follicle fruit

• dry fruit

• unilocular with multiple seeds

• splits along one seam only

• ex: milkweed and magnolias

silique fruits

• dry fruit

• two fused carpels with length longer than width

• seeds attached to a thin septum in the middle

• splits along two seams

• ex: canola

caryopsis fruit

• dry fruits

• pericarp is directly fused with the seed coat

• large starchy endosperm

• ex: grains

fleshy fruit types

• pome

• drupe

• berry

• pepo

• hesperidium

pome fruits

• fleshy fruit

• hypanthium/floral tube becomes the fleshy part

• true fruit is tougher and in the middle

• accessory fruit

• ex: apples and pears

drupe fruit

• fleshy fruit

• stone fruits

• exocarp is skin like

• mesocarp is fleshy

• endocarp is the stone

• ex: peaches, coconut

berry fruits

• fleshy fruit

• simple - single flower and single ovary

• exocarp skin-like

• mesocarp and endocarp are fleshy or pulpy

• ex: tomato, banana

pepo fruits

• fleshy fruits

• berry with a thick inseparable exocarp

• fleshy mesocarp and endocarp

• ex: melon and cucumber

hesperidium fruit

• fleshy fruits

• berry with a thick and leathery pericarp

• with juicy locules and seeds on the inside

• ex: lemons and oranges

identify a-m

a. anther

b. microsporocytes

c. microsporangium

d. microsporocyte (diploid)

e. meiosis

f. 4 haploid microspores

*for got to label next arrow as mitosis

g. generative nucleus

h. tube nucleus

g and h together = pollen grain

i. pollenation

j. germination on stigma

k. sperm nuclei

l. pollen tube

m. tube nucleus

1. identify the whole structure (A)

2. identify b and c

1. anther

2. b- microsporangia  c- microsporocytes

identify the structures in the image

pollen grains (male gametophytes)

identify a-q

a. megaspore mother cell

b. female meiosis

c. functional megaspore

d. degenerated megaspores

e. eight-nucleate stage cell

f. nuclei

g. cellularization

h. anitpodal cells

i. central nuclei

j. synergid cells

k. egg cell

l. nuclei migration

m. antipodal cells

n. central nuclei

o. synergid cells

p. egg cell

q. micropile

identify a-g on the female sporangium

a. ovule

b. integuments

c. megasporocyte

d. ovule

e. megasporocyte

f. carpel

g. ovules

identify a-d on the embryo sac

a. antipodal cells

b. polar nucleus

c. egg

d. synergid cells