Ch 21 Plant Responses and Reproduction
生醫系劉秉慧
分機 11815
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Plant Responses and Reproduction
I.Responses in flowering plants
1-5 Plant hormones
6. Environmental stimuli and plant responses
7. Photoperiodism
II. Sexual reproduction in flowering plant
1. Plant life cycle
2. Flowers
3. From spores to fertilization
4. Development of the seed in a eudicot
5. Fruit types and seed dispersal
6. Germination of seeds
III. Asexual reproduction in flowering plants
1. Propagation of plants in tissue culture
2. Genetic engineering of plants
I. Responses in Flowering Plants
• Plants change their growth and physiology in
response to environmental stimuli.
– Light, Gravity and Seasonal changes
• Plants also have plant hormones that help
control plant responses to these stimuli.
• There are five recognized plant hormones.
– Auxins, Gibberellins, Cytokinins, Abscisic
acid and Ethylene
– There are also man-made analogs of these
chemicals that can also regulate plant
responses to the environment
1. Plant hormone: Auxins (生長素)
• Auxins such as indoleacetic acid (IAA) are the most
common plant hormone.
• Auxins are produced in the shoot apical meristem.
found in young tissues, including young
leaves, flowers, and fruits.
• Auxins control plant growth and development.
– a key role in cell elongation.
– responsible for apical dominance.
– Application of auxins induces rooting of woody plant
cuttings.
– Auxin production by seeds enhances the maturation
of fruit.
Auxins
Shadly site undergo elongation
Acidity activates enzymes, causing the
cell wall to weaken, and water to enter
The cell. The cell then elongates
Effects of auxin: Aplical dominance
(頂芽優勢)
生長素
- 相關於向光和向地性
合成生長素
- 2,4 D 除草劑
2. Plant hormone: Gibberellins (吉貝素)
• The primary effect of gibberellins (GAs) is a
stimulation of stem elongation.
• GAs are involved in seed germination.
– GAs reverse the dormancy of the embryo.
– In seeds, GAs also stimulates the production of
amylase, (澱粉水解酶) which helps breakdown the
stored endosperm to provide the embryo with
sugars for energy.
Gibberellins-promote stem elongation
3. Plant hormone: cytokinins (細胞分裂素)
• Cytokinins are found in actively dividing tissues
(meristem) where they promote cell division.
• Effects of cytokinins:
- can slow the process of senescence in leaves.
- interact with auxins to coordinate the
development of plant roots and shoots.
4. Plant hormone: abscisic acid (離層酸)
• Abscisic acid (ABA)
is produced by all green
plant tissues.
• ABA has two main
functions in plants.
- ABA is involved in seed
and bud dormancy:
秋冬之際ABA增加
-ABA contributes to
the closure of stomata
to prevent water loss
in drought conditions.
(嫩芽)
Role of abscisic acid in stomata closure
逆境激素
5. Plant hormone: ethylene (乙烯)
• Ethylene is a gaseous hormone.
– A primary effect of the
ethylene is the abscission of
leaves (speed the process of
senescence ).
– Ethylene is involved in the
ripening of fruits like apples
and bananas.
催熟
6. Plant tropisms
(i) Plant response are strongly influenced by
environmental stimuli.
– Light intensity and wavelength
– Day length
– Gravity
– Touch
(ii) A tropism (向性) involves directional growth of
a plant towards or away from a stimulus.
– Phototropism : movement in response to light.
– Gravitropism(向地性): movement in response to
gravity.
– Thigmotropism (向觸性): in response to touch.
Plant tropisms typically involve differential
patterns of growth induced by auxins
The accumulation of auxin
on the shady site of the stem
Negative gravitropism: The
accumulation of auxin on
the lower site of the stem
Positive gravitropism
7. Photoperiodism (光週期性)
(i) Flowering in plants is a response to seasonal
changes and photoperiod (the ratio of the length of
day to the length of night over a 24-hour period).
–
Short-day/long-night plant flowers when the night
length is longer than the critical length.
–
Long-day/short-night plant flowers when the night
length is shorter than the critical length.
–
The flowering of day-neutral plants is not
influenced by photoperiod.
- Leaves are the parts stimulated by photoperiod
Photoperiodism (光週期性)
- The length of continuous darkness controls flowering
菊花,大豆
菠菜,蘿菠
(ii) Phytochrome (光敏素) and Plant Flowering
• Plants sense the photoperiod with a pigment called
phytochrome.
• Besides its role in flowering, phytochrome plays other
roles in plants.
– Sensing light conditions during germination
– Influencing leaf expansion and stem branching
Plant Responses and Reproduction
I.Responses in flowering plants
1-5 Plant hormones
6. Environmental stimuli and plant responses
7. Photoperiodism
II. Sexual reproduction in flowering plant
1. Plant life cycle
2. Flowers
3. From spores to fertilization
4. Development of the seed in a eudicot
5. Fruit types and seed dispersal
6. Germination of seeds
III. Asexual reproduction in flowering plants
1. Propagation of plants in tissue culture
2. Genetic engineering of plants
III. Asexual reproduction in flowering plants
• Because plants have non-differentiated
meristem tissues, they are totipotent(全能性),
meaning that a single cell can be used to
regenerate an entire plant in tissue culture.
• Specific combinations of plant hormones are
needed to control this development.
• These totipotent cells or fragments or the
plant can be used to vegetatively (asexually)
propagate plants- no genetic recombination.
(i). Propagation of plants in tissue cultures
原生質體
癒合體
(ii). Propagation of plants by
(地下莖)
(iii) genetic engineering of plants
• Genetic engineering can be used to transfer
genetic information from another organism
to plant cells, creating a transgenic plant.
(抗蘇力菌)
• Genetic engineering has been used extensively
to improve agricultural plants.
– Increased pest resistance
– Resistance to certain herbicides
– Tolerance to toxic elements and salinity
– Increased disease resistance
– Increased nutritional content
– Increase yield and productivity
• Commercial products
– Human hormones (Insulin, HGH)
– Clotting factors (VIII治療血友病)
– Antibodies
– Vaccines
Plant Responses and Reproduction
I.Responses in flowering plants
1-5 Plant hormones
6. Environmental stimuli and plant responses
7. Photoperiodism
II. Sexual reproduction in flowering plant
1. Plant life cycle
2. Flowers
3. From spores to fertilization
4. Development of the seed in a eudicot
5. Fruit types and seed dispersal
6. Germination of seeds
III. Asexual reproduction in flowering plants
1. Propagation of plants in tissue culture
2. Genetic engineering of plants
II. Sexual Reproduction in Flowering
Plants
1. Plant life cycle
(i) The plant cycle is an alternation of generation
between different multicellular forms of the
plant.
- The diploid, spore-producing sporophyte
- The haploid, gamete-producing gametophyte
(ii) For flowering plants, the sporophyte is the
dominant, flowering-producing generation.
(iii) Flowers produce two kinds of spores.
– Microspores that develop into the male gametophyte
(a pollen grain)
– Megaspores that develop into the female gametophyte
(an embryo sac)
– Flower pollen carries sperm to the flower
egg in the embryo sac.
- After the sperm in the pollen has fertilized the egg,
an embryo develops within the flower.
- The structure that houses the embryo
becomes the seed.
2. Flowers
(i) Flowers serve several important functions.
– Production of spores
– Protection for gametophytes
– Attraction of pollinators
– Pollen dispersal
(ii) Floral structure
- Monocots have multiples of three
- Eudicots have multiples of four or five.
- The sepals(花萼) protect the flower.
- The petals (花瓣) are colored to attract pollinators.
- The male portion of the flower, consisting of the
stamen (雄蕊), anther (花藥), and filament.
- The female portion of the flower, or carpel (心皮),
consisting of the stigma (柱頭), style (花柱), ovary(子
房), and ovules(胚珠)
3. From Spores to Fertilization
(i) The flower anther (花藥) produces male
microspores, which divide mitotically to
form pollen(花粉).
(ii) The pollen is released from the anther.
(iii) Within the ovule, female megespores
undergo mitosis to produce the egg.
(iv) During pollination, a pollen grain is
transported to the stigma.
(v) The pollen tube germinates and extends a
pollen tube to the ovule.
(vi) The pollen tube delivers two sperms to the
eggs to carry out double fertilization.
(vii) The sperms are involved in two fusion
events.
– One sperm fuses with an egg to form a
diploid zygote.
– The other sperm fuses with two other ovule
cells to form the triploid endosperm(胚乳).
(viii) The ovule develops into the seed, bearing
the embryo and the stored nutrients.
4. Fruit Types and Seed Dispersal
(i) a great diversity in the types of fruits
– Fruits can be dry or fleshy.
– Fruits can be simple, as for cereal grains.
– Nuts can have a hard shell that surrounds a single
seed.
– Legumes are fruits with several seeds.
(ii) seeds must be dispersed in order to germinate.
– have hooks that allow the seed to cling to
the fur of animals.
– pass through the digestive tract of animals
– dispersed by wind or water.
– dispersed in a projectile-like fashion
5. Germination of Seeds
(i) Seed germination is a programmed
developmental process during which the
embryo breaks dormancy and continues its
development.
(ii) Seed germination only occurs when
sufficient moisture, temperature, and oxygen
is present to sustain growth.
Germination of Seeds – an eudicot
•Eudicot seeds have three main parts.
–The seed coat is a protective layer.
–The endosperm provides a food
reserve.
–A plant embryo is present.
Germination of Seeds –a monocot