Download factors influencing seed germination

Champter VIII
Plant Growth and Movement
Key points:
Seed germination
Plant tissue culture
Plant growth
Plant movement
§1 Seed Germination(种子萌发）
Seed germination is the resumption of embryo growth, in general,
the radicle goes out the seed coat, depend upon a number of factors.
1.
Main factors influencing seed germination:
Water, O2, Temp., Light
(1)
Water
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soften the seed coat, radicle elongates easily.
O2 permeability, embryo metabolism rises.
gel to sol activates enzymes.
stored macromolecular substance hydrolysis
Plant hormone from the conjugate to free form.
30-70% water content for starchy seed germination and
more than 110% for protein seed (soybean) germination.
(2) Temperature
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Three cardinal points: “minimum, optimum
and maximum”
Optimum temperature of germination is the
temperature at which seeds germinate fastest
with highest germination rate.
The larger difference (10℃) between day and
night favors to germination.
The sowing should be conducted at the
temperature 2-3℃ above the minimum
temperature in production.
(3) O2
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Sufficient O2——active metabolism——growth—
—fast germination.
Deficient O2——anaerobic respiration——over
exhausting stored substance and alcohol
toxification.
Oil seeds (soybean, peanut, sun flower require
more O2 than starchy seeds (wheat, corn), RQ<1 。
Shallow-sowing in practice.
(4) Light
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Light seed: germination needs light
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Dark seed: germinate well under darkness.
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controlled by red light（660nm） and far-red light
(730nm).
e.g. tobacco, lettuce, Arabidopsis thaliana
e.g. Citrullus (西瓜属)
Photophobic seed：germination inhibited by light
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e.g. eggplant, tomato, onion
2 Biochemical changes during germination
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Water absorption: rapid→slow→rapid
(matrix to osmotic absorption)
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I: imbibtion; II: physiological changes: III: growth
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Respiration:
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From anaerobic respiration to aerobic respiration
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Organic substances:
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Starch → glucose
Fat → organic fatty acid
Protein → amino acids
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Enzymes:
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From boundary enzyme → free enzyme
De novo synthesis
Hormones:
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From boundary enzyme → free enzyme
De novo synthesis
3. Seed longevity and vitality
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Seed longevity （种子寿命）: Time experienced
from seed maturation to loss of the germination.
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most crops 1-3years, lotus seed:1000years, pillow: 12h.
Seed vitality （种子生活力）and Seed vigor（种子
活力）:
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Seed viability is the potential ability to germinate
Seed vigor is the ability to germinate, grow and produce in
the field. It is a complicated term refers to many traits of
plants represented by vigor index (Vi).
Germination rate (Gr) is percentage of germinated seeds,
Gr= number of germinated seeds/ total seedsX100
Vi=SX∑Gt/Dt, where S refers to average fresh weight of
shoot or roots; Gt: number of germinated seeds at the day
(t); Dt : days of seed germination.
Methods to measure seed vitality
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TTC(氯化三笨四氮唑）
BTB（溴麝香草酚蓝）
Red ink staining
Fluorescence
BTB Gelatin
Red ink dyeing
§2
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plant growth and development
Development（发育） refers to the sum of all of the
changes that an organism goes through in the life
cycle－from germination of the seed through growth,
maturation, flowering, seed formation, and
senescence, it is a qualitative term. Generally
speaking, refers to the vegetable to reproduction.
Growth（生长） is an irreversible increase in size
number and mass. It is a quantitative term. Cell
growth consists of division, volume increase and
differentiation.
Differentiation（分化） refers to qualitative
changes that accompany growth. It leads to
morphological, structural and functional changes of
plants
Differentiation occur in various levels
Organs
Tissues
Cells
Xylem phloem
Molecules
Root,stem
Conductive
Leaf flower
fruit
Absorptive
Mechanic
Aerenchyma
storage
Eye
Microscope electron microscope biochemical
molecular biology
Root hairs…
genes,protein
Enzyme
The Analysis of Plant Growth
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Plant Growth Can Be Measured in
Different Ways
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Fresh weight
Dry weight
Cell number
Length or height
volume
Plant Growth Can Be Described in Both
Spatial and Material Terms
1. Cell division
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Factors influencing cell division
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Hormones:
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IAA
GB
CTK
Vitamines:
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VB1, VB2 and Niacin(VB3) stimulate cell division
Hormones control the cell cycle in plants
2 Cell elongation
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Morphology ： cell volume increase
dramatically as the cell absorbs a great
number of water. Combine small vacuoles
into a central vacuole so that the nucleus and
cytoplasm is pressed to the side toward cell
wall.
Water is the most important factor for cell
elongation, naturally involves a lot of material
synthesis and accumulation.
•GA, IAA and CTK control cell elongation
Cell elongation depends on the elongation
of cell wall
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Components of cell wall
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Cell wall is composed of :
Cellulose
Hemi-cellulose
Pectin
Structural protein
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Cell wall is a net work
4. Cell Differentiation
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Keep volume steady and change in
morphology and function.
Factor affecting differentiation.
(1) Plant hormone：IAA/CTK : rooting;shooting
(2) Sucrose：lower (1.5-2.5%) sucrose is advantage
to xylem differentiation and higher （>4%) to
phloem. Middle (2.5-3.5%) to both and the
concentration can induce cambium.
(3) Light：poor differentiation without light.
(4) Polarity : The tissues
and organs are arrayed
in a precise order along
a linear axis that
extends from the shoot
apical meristem (SAM)
at one end to the root
apical meristem (RAM)
at the other. Upend
gives rise to bud and
basal end does root.
(5) Uneven division of cells.
5. Plant Tissue Culture（植物组织培养）
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Plant Tissue Culture（植物组织培养）, also called
micropropagation, is a technique used to propagate
cells, tissue, organ and plants under sterile
conditions using explants and artificial growth
medium, often to produce clones of a plant .
The theory basis for plant tissue culture is
Totipotency（细胞全能性）refers to all differentiated
plant cells retain all the genetic information required
for the development of a complete plant. (exception:
dead cell or cell without nucleus)
Advantages using tissue culture over
traditional propagation
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The production of exact copies of plants that produce particularly
good flowers, fruits, or have other desirable traits.
To quickly produce mature plants.
The production of multiples of plants in the absence of seeds or
necessary pollinators to produce seeds.
The regeneration of whole plants from plant cells that have been
genetically modified.
The production of plants from seeds that otherwise have very low
chances of germinating and growing, i.e.: orchids(兰花） and
nepenthes（猪笼草）.
To clean particular plant of viral and other infections and to
quickly multiply these plants as 'cleaned stock' for horticulture
and agriculture
Orchids
Other Applications
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Micropropagation can be used to produce large numbers of
identical individuals.
Micropropagation can also be used to conserve rare or
endangered plant species.
A plant breeder may use tissue culture to screen cells rather than
plants for advantageous characters, e.g herbicide
resistance/tolerance.
Large-scale growth of plant cells in liquid culture inside
bioreactors as a source of secondary products, like recombinant
proteins used as biopharmaceuticals.
To cross distantly related species by protoplast fusion and
regeneration of the novel hybrid.
To cross-pollinate distantly related species and then tissue
culture the resulting embryo which would otherwise normally die
(Embryo Rescue).
1) Culture medium
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5 groups of ingredients
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Minerals such as N P S K Ca Mg Fe Mo Zn
Cu B
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Carbon source: usually sucrose of 2-4%
Vitamins: thiamin(VB1), niacin(VB3), inositol,VB6
Organic addictives: such as coconut milk, yeast
power.
Plant growth regulators: such as 2,4-D, NAA, KT,
BA
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Culture medium can be made as fluid or solid
by adding argar of 0.6-0.7%.
Culture medium should be sterilized by a
autoclave.
The optimum temp is about 23-28℃
The optimum light intensity is 500~800mol
m-2s-1, generally 600mol m-2s-1 is enough.
2) Explant (外植体）
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The tissue which is obtained from the plant to
culture is called an explant.
Theoretically, a totipotent explant can be
grown from any part of the plant. However, In
many species explants of various organs vary
in their rates of growth and regeneration,
while some do not grow at all. Growing
explants are easily to start cell division.
Appendix: ways of getting regenerated
plants
1. Callus pathway (organ regeneration pathway)
explant→callus→new plant
1)
Adventitious roots → → →adventitious bud
2)
Adventitious bud → → →adventitious root
3)
Adventitious root and bud simultaneously
-----------------------Dedifferentiation （脱分化） is a process of regression of a
specialized cell or tissue to a simpler, more embryonic,
unspecialized form.
Redifferentiation （再分化）is a process by which a group of
once dedifferentiated cells differentiate to specialized
forms.
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2. Embryoid pathway:
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Develop from a somatic embryo （体细胞胚）to a
whole plant, just like from zygotic embryo to whole
plant. It also experiences “Early globular stage”,
“heart stage”, “ Torpedo stage” and “Mature
embryo”.
Cluster seedling pathway:
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Use buds as explant
§3 Plant growth
1.
Grand period of plant growth（植物生
长大周期）
Grand period of plant growth refers to
that the growth of tissues, organs and
even a whole plant exhibit a typical
model with “slower-faster –slower” in life
cycle. The total growth appears S-shape
growth curve---logistic curve.
Grand growth period
Growth curve
Time
2. Factors influencing plant growth
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1) Light
2) Temp.
3) Water
4) Minerals
5) others
1) Light
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Indirect：by photosynthesis and
transpiration. (High energy)
Direct：photomorphogenesis. (Low energy)
High irradiation inhibit plant gowth
Blue light, UV inhibit plant growth
2) Temperature
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Three cardinal points:
“minimum, optimum and maximum temperature for
growth”
Optimum temperature for growth is the
temperature at which plant grows fastest but not
strongest.
Suboptimum temperature for growth is the
temperature at which plant grows slower but
strongest than at optimum temperature .
Difference in temperature between day and night
(thermoperiodicity of growth: 生长的温周期 or daily
periodicity of growth: 生长的昼夜周期 ) controls
plant growth.
3).Seasonal periodicity of growth
mainly controlled by temperature, light and
water. General speaking, slowly in the Spring,
fast in the summer and again slowly in the
autumn, stop in the winter.
4).Water, O2 and minerals
“Dry for root, wet for bud”.
Water,
Oxygen,
Minerals
3. Plant growth correlation
（植物生长的相关性）
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The growth among the different organs in a
whole plant coordinates and inhibits each
other, which is called the plant growth
correlation.
The correlation mainly includes
root and shoot,
stem and branch
vegetable organs and reproductive organs.
1) Root vs. Shoot
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Shoot provides photoassimilate, IAA and
VB1 to roots；
Root provides water, mineral nutrition,
plant hormones (CTK、GA, ABA) and
partial AA to shoot.
They must coordinate each other.
Root-shoot ratio（根冠比）
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Root-shoot ratio is an index for the coordinative between root
and shoot, expressed as root weight/shoot weight:
Factors influencing root-shoot ratio and its regulation
(1) H2O soil water content↓，the ratio↑.
(2) Regulation with nutrition
• N↑, the ratio↓；N↓， the ratio ↑.
• Leaf vegetable applied with heavy N.
• P and K↑ the ratio ↑.
• Tuber root applied with much P and K.
(3) Sufficient light ↑ the ratio ↑.
(4) Temperature ↓， the ratio ↑.
(5) Tilling and breaking roots in the surface of soil，the ratio↑.
Main stem and Branch
—— Apical dominance(顶端优势）
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The phenomenon that main stem apices
grows fast and axillary bud or branch grows
slowly of a plant is called apical dominance .
The reasons for dominance:
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(1)Nutrition hypothesis (K. Goebel,1900);
(2)IAA hypothesis---direct-inhibition model
(Thamann and Skoog, 1934) , IAA inhibits branch;
(3) Nutrition supply and plant hormone (IAA, GA
and CTK) control theory
Apical dominance of a tree
Vegetative Vs. Reproductive growth
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The better vegetation promotes reproduction
and the poorer vegetation results in poorer
reproduction .
Over-vegetation inhibits reproduction.
Overgrowth often gives rise to late flowering,
bad setting, fruit falling and yield decreasing.
Over-reproduction reduces the vegetative
organ development and leads to plant
premature, for fruit tree, leads to “big and
small year”.
Locomotion
Movement
Animal such as bee
In dark
Under sunlight
§4 Plant movement
Tropical movement (向性运动）
 Nastic movement（感性运动）
 Rhythm movement（昼夜节律）
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1. Tropic movement
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Tropical movement is the movement caused by
unilateral stimulus, e.g. phototropism, gravitropism,
chemotropism and hydrotropism.
1) Phototropism
Positive phototropism
(正向光性）:
Sunflower
Negative phototropism
(负向光性）:
Air roots
Diaphototropsm
(横向光性）::
leaves
2) Gravitropism
Positive gravitropism
(正向重力性）:
Roots
Orthogravitropism
(负向重力性）:
Shoot
Diagravitropism
(横向重力性）:
subterraneous stem
Statolith (平衡石）is the
amyloplast in the root
cap, each amyloplast is
composed of 1-8 starch
grains. One cell contains
about 4-12 amyloplasts.
Figure 18.11
Root cap perceive gravity. Removing root cap will not affect
growth response but the gravitropic response is abolished.
Regeneration of root cap requires gravity and plants can
respond to gravity after root cap is regenerated. The columella
cells (中柱鞘细胞）are the most sensitive cells for sensing
gravity.
Figure 18.16
2. Nastic movement
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Movement is caused by stimulus of no
direction.
Include: growth movement( irreversible) and
turgor movement (reversible)
1) Nyctinasty movement（感夜运动）
Maranta (竹芋） at afternoon (left) and in the
night (right)
2) Seismonasty（感震运动）
The sensitive plant (Mimosa
pudica) have special structures
(pulvinus) at the bases of petioles
and leaflets that allow the leaf
parts to close up when touched
(arrow).
Pulvinus（叶褥）
Structure of ventral (腹侧） and dorsal (背侧）motor cells in the pulvinus
3. Circadian rhythm （近似昼夜节奏）
or physiological clock （生理钟）or
biological clock（生物钟）
Some movement is controlled by inherent
factors such as such as oxygen evolution
and respiration, alternately through highactivity and low-activity phases with a regular
periodicity of about 24 hours, this movement
is called Circadian rhythm or physiological clock or
biological clock.
菜豆叶在恒定条件（微弱光，20℃）下的运动
Figure 19.15
Basic model of circadian clock
Figure 19.16
Clock gene
(CCA1?)