Biology of Plants and Their Reproduction

Requires two parents

Female flowers – carpel

Male flowers – stamen

Fusion of gametes to produce new individuals - fertilization

Offspring produced are different from the parents – genetic variation

Gametophyte

Male gametes

Female gametes

Fertilization

known as double fertlization

This is due to the the sperm fuses with the egg cell forming a zygote (2n) and another sperm fuses with the polar nuclei forming triploid endoseprm (3n)

Requires one parent

Vegetative propagation

Vegetative propagation

Offsprings are identical to parents

Examples

Budding

T-budding

Patch budding

Grafting

Whip-and-Tongue Graft

Splice Graft

Cleft Graft

Wedge Graft

Stem cutting

Advantages

The offsprings are genetically identical and therefore advantageous traits can be preserved.

It is faster. Organisms multiply quickly

Many plants are able to tide over unfavorable conditions. This is because of the presence of organs of asexual reproduction like the tubers, corm, bulbs, etc

Vegetative propagation is especially beneficial to the agriculturists and horticulturists

They can raise crops like bananas, sugarcane, potato, etc that do not produce viable seeds

Disadvantages

gradually lose their vigor as there is no genetic variation. They are more prone to diseases that are specific to the species. This can result in the destruction of an entire crop

Since many plants are produced, it results in overcrowding and lack of nutrients

A process of transferring pollen grain onto the stigma of a flower

Types

Abiotic

Wind

Water

Biotic

Insects

Birds

Mammals

Mechanism

Self-pollination

One flower pollinates the same flower on the same plant

Cross pollination

Transfering of pollen to another flower on different plant

Some plants produce fruit containing seeds

Mature ovary

Tissue surrounding the embryo develops into fruit.

When the fruit is fully developed it drops off the plant, or is carried away by an animal

When fruit decomposes it releases the seed and germination can occur

A matured ovule containing an embryo which is usually the result of sexual fertilization

A protective outer covering

Storage tissue

An embryo

Seed Structure

Seed coat

Endosperm

Plumule

Radicle

Benefits

Spread progeny to colonize new environments

Major way plants reproduce in nature

Seedling = plant produced from seed

Stages of seed development

Stage I: Histodifferentiation

Embryo reaches the stage of developing cotyledons

Fresh and dry weight increases

Stage II: Cell Expansion

Rapid cell enlargement

Food reserves accumulate

Carbohydrates (starch)

Storage proteins

Lipids (oils/fats)

Different species accumulate reserves in different amounts

Stage III: Maturation Drying

Seeds are physiologically mature

Maximum dry weight is reached

High germination potential (viable and vigorous)

Rapid water loss

Vascular connection between “mother” plant and seed is severed

Seeds usually will not germinate when surrounded by fruit

Types of Seed

orthodox seeds

relatively small-seeded.

, these seeds can tolerate drying to as low as 5% moisture content under common conditions and low storage temperatures

Their life span is, in fact, prolonged with low seed moisture and temperature

recalcitrant or drying-sensitive seeds

are “readily killed by drying, most especially if their moisture content falls below the critical value ranging from 12-30%.

generally cannot withstand temperatures lower than 20 C, partly because of the high moisture content which renders the seed prone to chilling or freezing injury.

Some can maintain viability at slightly lower temperatures but vigor of the seedling may be affected

Quiescent seed

after maturation drying seeds fail to germinate since they are dry

after maturation drying seeds fail to germinate since they are dry

Dormant seeds

Fail to germinate even with favorable environmental conditions

Viviparous

seeds germinate prematurely on the plant (also called “precocious germination”)

Undesirable trait

Occurs on wheat and corn

Occurs on citrus and tomato

Due to a genetic mutation and environmental conditions

Reduced ABA production or insensitivity to ABA

Parthenocarpy

Fruit development without seed formation

Vegetative = fruit develops without pollination

desirable in greenhouse food crops such as

Cucumber

Tomato

Grapes

Can be artificially induced by spraying plants

Tomatoes respond to auxin

Grapes respond to GA

Simple Fruits

Single ovary

Can be fleshy or dry

Cherry

Soy bean pod

Aggregate Fruits

Arise from a single flower with several carpels

Blackberry

Multiple Fruits

Arise from an inflorescence

Many flowers

As the walls of the many ovaries thicken,
they fuse and become one fruit

Pineapple