Biology of Plants and Their Reproduction

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Biology of Plants and Their Reproduction

Types of fruit

Multiple Fruits

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

Pineapple

Arise from an inflorescence

Many flowers

Aggregate Fruits

Arise from a single flower with several carpels

Blackberry

Simple Fruits

Can be fleshy or dry

Soy bean pod

Cherry

Single ovary

Development of Seeds

Types of Seed

Parthenocarpy

desirable in greenhouse food crops such as

Can be artificially induced by spraying plants

Grapes respond to GA

Tomatoes respond to auxin

Grapes

Tomato

Cucumber

Vegetative = fruit develops without pollination

Fruit development without seed formation

Viviparous

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

Reduced ABA production or insensitivity to ABA

Due to a genetic mutation and environmental conditions

Occurs on citrus and tomato

Occurs on wheat and corn

Undesirable trait

Dormant seeds

Fail to germinate even with favorable environmental conditions

Quiescent seed

after maturation drying seeds fail to germinate since they are dry

recalcitrant or drying-sensitive seeds

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

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.

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

orthodox seeds

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

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

relatively small-seeded.

Stages of seed development

Stage III: Maturation Drying

Seeds usually will not germinate when surrounded by fruit

Vascular connection between “mother” plant and seed is severed

Rapid water loss

High germination potential (viable and vigorous)

Maximum dry weight is reached

Seeds are physiologically mature

Stage II: Cell Expansion

Different species accumulate reserves in different amounts

Food reserves accumulate

Lipids (oils/fats)

Storage proteins

Carbohydrates (starch)

Rapid cell enlargement

Stage I: Histodifferentiation

Fresh and dry weight increases

Embryo reaches the stage of developing cotyledons

Benefits

Seedling = plant produced from seed

Major way plants reproduce in nature

Spread progeny to colonize new environments

Seed Structure

Radicle

Plumule

Endosperm

Seed coat

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

An embryo

Storage tissue

A protective outer covering

Fruit formation

When fruit decomposes it releases the seed and germination can occur

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

Tissue surrounding the embryo develops into fruit.

Mature ovary

Some plants produce fruit containing seeds

Pollination

Mechanism

Cross pollination

Transfering of pollen to another flower on different plant

Self-pollination

One flower pollinates the same flower on the same plant

Types

Biotic

Mammals

Birds

Insects

Abiotic

Water

Wind

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

Asexual Reproduction

Disadvantages

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

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

Advantages

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

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

It is faster. Organisms multiply quickly

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

Examples

Stem cutting

Grafting

Wedge Graft

Cleft Graft

Splice Graft

Whip-and-Tongue Graft

Budding

Patch budding

T-budding

Offsprings are identical to parents

Vegetative propagation

Requires one parent

Sexual Reproduction

Fertilization

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)

known as double fertlization

Gametophyte

Female gametes

Male gametes

Offspring produced are different from the parents – genetic variation

Fusion of gametes to produce new individuals - fertilization

Requires two parents

Male flowers – stamen

Female flowers – carpel