NOTES: Plant Reproduction and Development (Ch 38)

NOTES: CH 38 - Plant Reproduction

*Modifications in reproduction were key adaptations enabling plants to spread into a variety of

.

* Water has been replaced by and as a means for spreading gametes.

* Embryos are protected in SEEDS.

* Vegetative (asexual) reproduction for propagation of some plants in a variety of environments.

Our focus in this chapter will be…SEXUAL REPRODUCTION

 GAMETOPHPYTES: reproductive structure of plants

-.

(sperm and egg cells)

-gametes fuse to form a (2n) that develops

into a multicellular plant

…ALTERNATION OF GENERATIONS!

FLOWERS:

-the reproductive structure of angiosperm sporophytes

-four sets of modified leaves:

1)

2)

3): -anther, filament

4): stigma, style, ovary

STAMENS and CARPELS (PISTILS) are the reproductive parts of the flower.

 Female gametes develop in , which contain the

 this occurs at the base of the carpel /pistil, inside the

 Male gametes develop in the stamen inside

 this occurs at the stamen tips within chambers of the

FLOWER VARIATIONS:

Complete flower = flower with

Incomplete flower = flower missing one or more of these parts (e.g. most grasses do not have petals on their flowers)

Perfect flower = flower having both(a.k.a. bisexual)

Imperfect flower=flower that is either (a.k.a. unisexual)

Monoecious = “one house”; plants with both staminate and carpellate flowers on the same plant (ex: )

Dioecious = “two houses”; plants having staminate and carpellate flowers on separate plants (ex: )

Development of the Male Gametophyte (POLLEN):

POLLEN GRAIN = the immature male gametophyte; develops within the anthers of stamens in an angiosperm

 extremely durable; tough coat to prevent biodegradation

at the time of pollination:

A pollen gain consists of 2 cells (both haploid):

-GENERATIVE CELL:

-TUBE CELL: ; contains the generative cell

Development of the Female Gametophyte (EMBRYO SAC)

● Female gametes are contained in the EMBRYO SAC(diagram of embryo sac below):

Embryo Sac:

egg cell (OVUM) at one end

ovum flanked by 2 syngerids (help to attract sperm cells)

 two nuclei in center (“polar nuclei”)

POLLINATION:

-occurs when wind- or animal-born pollen released from the anthers lands on the STIGMA at the tip of the carpel

POLLINATION=

Methods of Pollination / spread of pollen:

•

•

• (most plants cross-pollinate)

To prevent self-pollination (and thus ensuring sperm and egg from different plants meet), some plants:

-have stamens and carpels that ;

-have structural arrangement of flower parts that reduces the chance of pollen getting transferred from stamen to carpel;

-are SELF-INCOMPATIBLE (a biochemical block that prevents the pollen grain from developing and fertilizing the egg)

SELF-INCOMPATIBILITY: from the same, or closely related, plant by the stigma

after POLLINATION…

-pollination is followed by this sequence:

1) a pollen tube grows from the pollen grain, down the carpel, into the embryo sac;

2) sperm are discharged resulting in fertilization of the eggs;

3) the zygote develops into an embryo;

4) as the embryo grows, the ovule surrounding it develops into a ;

5) while seed formation is taking place, the entire ovary is developing into a , which will contain one or more seeds.

DOUBLE FERTILIZATION:

When a compatible pollen grain lands on a stigma of an angiosperm, double fertilization occurs.

DOUBLE FERTILIZATION = with two cells of the embryo sac

Steps:

1) pollen grain adheres to stigma, germinates, and extends a pollen tube toward the ovary;

2) generative cell divides (mitosis) to form 2 sperm;

3) directed by a chemical attractant, pollen tube enters and discharges its 2 sperm nuclei into the embryo sac;

4) 1 sperm unites with the egg ;

5) other sperm combines with the 2 polar nuclei to form a 3n (triploid) nucleus in the large central cell of the embryo sac.

 this central cell will give rise to the (a food storing tissue for the seed/embryo)

**after double fertilization, each ovule develops into a seed and the ovary into a fruit surrounding the seed(s).

ENDOSPERM:

• (which it provides to the developing embryo)

Structure of the mature seed:

in mature seeds, the embryo is quiescent (dormant) until germination

• the seed dehydrates until its water content is only 5-15% by weight.

• the embryo is surrounded by endosperm, enlarged cotyledons, or both.

• the seed coat is formed from the outer layers / integuments of the ovule.

Dicot seed structures:(diagram of mature dicot seed):

-cotyledons =

-hypocotyl = embryonic axis

-radicle =

-epicotyl = embryonic axis

*Seeds are dispersed from the source plant when fruits are moved about by the wind or animals.

*Seeds deposited in soil of the proper conditions (moisture, nutrients), will GERMINATE.

FRUITS:

-ovary develops into fruit (adapted for )

*Fruits ripen about the time seeds are becoming fully developed

Ripening fruits are characterized by:

1) fruit becomes softer as a result of enzymes digesting the cell wall components;

2) colors usually change and as organic acids or starch are converted to sugar;

3) these changes produce an edible fruit which entices animals to feed, thus !