External Factors And Plant Growth

Front 1

Back 1

Thigmotropism
Right: tendrils of the bur cucumber Cucumis anguria

Front 2

Back 2

Diurnal movement of wood sorrel leaves, Oxalis

Front 3

Back 3

Chrysanthemum, a short-day plantLeft: short-day conditions; right: long-day conditions

Front 4

Back 4

Morphogenic response of Poinsettia (flower formation) to short days

Front 5

Back 5

Spinach, a long-day plantLeft: short-day conditions; right: long-day conditions

Front 6

Back 6

Etiolated seedling needs exposure to red light to turn green
Etiolation: plant that is dark-grown, or under soil is thin and pale. They become green and sturdier when exposed to red light. Exposure to far-red light will cancel the effect

Front 7

Back 7

Thigmonastic movement (after touching) in Mimosa pudica

Front 8

Back 8

Venus flytrap thigmonastic movment

Front 9

Back 9

Thigmomorphogenesis
Regular rubbing inhibits elongation, but promotes radial expansion of plants
Left Arabidopsis plant was rubbed.

Front 10

Back 10

Heliotropism (of lupine)Leaves move and stay perpendicular to sun’s rays

Front 11

Back 11

Heliotropism (solar tracking) of sunflowers

Front 12

Tropism

Back 12

Bending of plant towards or away from stimulus
Positive: towards stimulus
Negative: away from stimulus

Front 13

1. Phototropism
2. Gravitropism:
3. Hydrotropism:
4.Thigmotropism:

Back 13

1.movement because of light
2.in response to gravity
3. in response to moisture
4. in response to touch

Front 14

The Floral Stimulus

Back 14

Florigen is the flowering substance.
It is formed in mature leaves and transported through the phloem to the apical meristem where it triggers a series of gene activities leading to flowers.
Florigen production seems to be dependent on day length.

Front 15

Vernalization

Back 15

Vernalization is exposure of plants to cold.
Needed for some plants to flower.
Takes place in shoot of apical meristem
Required for many biennials, winter annuals (sown in fall, bloom next spring)

Front 16

Dormancy

Back 16

Special condition of arrested growth.
Growth resumes when limiting conditions disappear
What are the triggers for growth for buds, seeds?
There are endogenous inhibitors that must be removed.

Front 17

Seeds and dormancy

Back 17

Environmental cues to break dormancy:
Warm temperatures after a long period of cold
Exposure to moisture after a period of drying
Abrasion by soil activities wearing away a protective coat: scarification
Microbial digestion of seed coat
Leaching away of inhibitory chemicals

Some seeds remain viable for a long time: a 2000 year old date palm; a 1300 year old lotus

Front 18

1. Nastic movements
2. Nyctinastic movement
3. Thigmonastic movements
4. Photonastic
5. Morphogenic responses
6. Taxis
7. Thigmomorphogenesis
8. Heliotropism

Back 18

1. non-growth response, no orientation with regard to direction of stimulus
2. sleep movement of leaves, vertical at night
3. (turgor changes)
4. opening and closing of flower parts: diurnal or nocturnal
5. fundamental changes in plants life stages (vegetative > reproductive)
6, cell swimming away from or towards stimulus (sperm cells of algae and some plants)
7. altering growth patterns: touching increases radial growth
8. solar tracking

Front 19

Pulvinus

Back 19

thickening at the base of plant parts that show nastic movements. Turgor change in parenchyma cells cause movement
Example: Mimosa pudica