9.3 Reproduction in Angiospermophytes

Dicotyledonous Flower Parts FUNCTION Sepals Protect the developing flower white in the bud Petals Modified leaves; often colourful to attract pollinators Stamen The “male” reproductive structure; made of anther and filament Anther Produces and releases pollen Filament Stalk of stamen that holds up anther Carpel The “female” reproductive structure; made of ovary, style, and stigma

Pistil Can refer to a single carpel or a group of fused carpels Stigma Sticky top of carpel which pollen lands on Style Supports and holds up the style; gives the stigma exposure to pollen ovary Base of carpel in which the female sex cells develop; if fertilization occurs, it will turn into a protective fruit Ovules Found in the ovary; contain female sex cells, eggs Pollen Contain male sex cells (sperm)

Flowers occur in various colours, shapes and types – reflective of their pollinator Complete flowers – contain all four basic flower parts (sepals, petals, stamen, and carpel) Incomplete flowers – lack at least one of these parts Staminate flowers – have only stamens Carpellate flowers – have only carpets

Pollination the process in which pollen (which contains the male sex cells –sperm) is placed on the female stigma. Can occur via a variety of vectors Wind water Insects Birds Bats

Angiosperms and their pollinators have coevolved (supported by fossil evidence) The flowers colours, patterns, odours, shapes and even the time of day it blooms are designed to attract a specific pollinator Often, the flower provides the gift of food to the pollinator in exchange for the pollinator unintentionally transporting pollen to the stigma

Examples Red flowers – pollinated by birds Yellow and orange flowers – bees Heavily scented flowers – nocturnal animals Inconspicuous, odourless flowers – wind

Cross Pollination – pollen lands on the stigma of a different plant. Self Pollination – when pollen from the anther of a plant falls on its own stigma A form of inbreeding – thus less genetic variation Cross Pollination – pollen lands on the stigma of a different plant. Increases variation and offspring with different fitness

Fertilization When the male and female sex cells unite to form a diploid zygote. The female sex cells are in the ovules. The sperm from the pollen that has attached itself to the stigma must make its way to the ovules in the ovary.

Pollen attaches to stigma and begins to grow a pollen tube through the style Within the growing pollen tube is the nucleus that will produce the sperm. The pollen tube completes growing by entering an opening at the bottom of the ovary The sperm moves from the tube to combine with the egg of ovule to form a zygote.

The Seed and Seed Dispersal Once the zygote is formed, it develops with the surrounding tissue into the seed As the seed is developing, the ovary around the ovule mature into a fruit Seed dispersal can be aided by water, wind, animals

SEED Is the means by which an embryo can be dispersed into to distant locations. It is a protective structure for the embryo

Seed Part Function testa Tough, protective outer coat cotyledons Seed leaves that function as nutrient storage structures microphyle Scar of the opening where the pollen tube entered the ovule Embryo root and embryo shoot Become the new plant when germination occurs

Pre-Germination Once seeds are formed, a maturation process follows. The seed dehydrates until the water content of the seeds is about 10 -15% of its weight. At this point, the seed goes into a dormant period where there is low metabolism and no growth or development. Duration is variable for different types of seed It is an adaptation to environmental conditions

FUN FACT In 1995, a team of biologists found some seeds in a dried-up lakebed. The seeds were from a type of lotus plant. After germinating some of the seeds, the biologists found them to be nearly 1300 years old!!! (They used radiometric dating to determine this age.)

Fun Fact In 2005, a 2000 year old Judean Date palm (found in the ruins of Herod the Great’s palace)was germinated

Germination Conditions If conditions become favourable, the seed will germinated. GERMINATION – is the development of the seed into a functional plant. There are several conditions that must be fulfilled for a seed to germinate.

WATER Required to rehydrate the dried seed tissues Makes the seed swell As a result the seed coat will crack and hydrolytic enzymes are activated- they will start to catabolize large molecules (storage polysaccharides such as starch is converted into maltose) for cellular respiration.

OXYGEN Required for the break down of those sugars in cellular respiration

TEMPERATURE Appropriate temperature is required, that is varied among plants depending on their natural environment. Ex. Period of low temperature followed by high temps – ensures that the seed does not geminate until the winter has passed. Temperature is important for enzyme activity

Many plants have specific conditions other than these that must be met in order to germinate. Ex:Lodgepole Pine

The emerging seedling is fragile and will be exposed to hard weather, parasites, predators, and other hazards. Many seeds will not produce a functional plant because of these threats To compensate, plants produce a large number of seeds

Metabolic Processes during Germination of a Starchy Seed Seed absorbs water (which leads to many metabolic changes) Gibberellin is released after the uptake of water Gibberellin – plant growth hormone

Gibberellin triggers the release of the enzyme amylase Amylase causes the hydrolysis of the starch into maltose Maltose is hydrolysed into glucose which can be used for cellular respiration or converted into cellulose to build cell walls for new cells

Stored proteins and lipids will also be hydrolyzed to make proteins/enzymes and phospholipids and energy metabolism. Germination uses the food stored in cotyledons to grown until it reaches light when it starts to photosynthesize

Control of Flowering Light important factor for growth and development Plants are able to detect the presence of light, its direction, wavelength, intensity PHOTOPERIODISM – the plant’s response to light involving the relative lengths of day and night.

*To ensure continued existence in an area, a plant must flower when pollinators are available and when necessary resources are plentiful

PLANT TYPE FLOWERING AND LIGHT EXAMPLES LONG-DAY PLANTS Bloom when days are longest and nights the shortest (midsummer) - Require Pfr Radishes, spinach, lettuce SHORT-DAY PLANTS Bloom in spring, late summer, and autumn when days are shorter - Inhibited by Pfr Poinsettias, chrysanthemums, asters DAY-NEUTRAL PLANTS Flower without regard to day length Roses, dandelions, tomatoes

It is actually the length of night that controls the flowering process. The control is brought about by a special blue-green pigment called phytochrome.

Phytochrome Phytochrome is a photoreceptor and a pigment It absorbs light There are 2 forms of phytochrome Pr – absorbs red light Pfr – absorbs far-red light/darkness

Far-Red Light Wavelengths between 700-800nm At the far end of the visible light spectrum (Between red light and infrared light)

During the day, when there is light, red light (wavelength of 660nm) is present Pr absorbs red light and is rapidly converted into Pfr At the end of the day, after many hours of light, plants will have most of their phytochrome in the form of Pfr

During the night, when there isn’t light (therefore no red light), Pfr is slowly converted back into Pr By morning, most of the phytochrome will be Pr again If there is even a flash of light interrupting the darkness during the night, it will disrupt the process of Pfr turning into Pr

Pr Pfr _____________________________________________________________ Pfr Pr

Long-day plants, require Pfr to flower Long day = short night! At the end of a short night, there will still be lots of Pfr remaining. The remaining Pfr at the end of a short night stimulates the plant to flower.

In short-day plants, the Pfr acts as an inhibitor for flowering. So after a short night, the remaining Pfr will prevent the plant from flowering. If it was a long night, all the phytochrome will be in the form of Pr (there will be no Pfr) so flowering CAN occur.