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
