Transcript Photoperiodic responses, light receptors and the biological clock

Photoperiodic
responses, light
receptors and the
biological clock
Classification according to photoperiodic control of flowering
Short Day Plants (SDP)
Flowering requires short days (long nights)
Long Day Plants (LDP)
Flowering requires long days (short nights)
Day Neutral Plants (DNP)
Flowering is not regulated by day length
Photoperiodism and flowering
Effect of day length on flowering
and other activities (seed
germination, seed dormancy,
bud break, bud dormancy) in
temperate regions of the
northern hemisphere.
Fig. 15-20, p. 252
How does a change in day length lead to the
induction of flowering?
For any biological organism to detect a change in
day length, it needs:
1) A day light detection mechanism (the
photoreceptors Phy and Cry)
2) A biological clock (set at a 24 hr cycle) as a time
measuring system
Example of a circadian rhythm:
The circadian oscillator controls the leaf movement rhythm in beans
Leaf angle
Leaf angle
Leaf angle
already
starts to
change
before the
light of day.
Leaf angle
changes
continue
their rhythm
also in
continuous
dark.
Circadian rhythms allow to monitor (to
visualize) the biological (circadian) clock
Without light detection (mediated by Phy and Cry receptors) the period of
the biological clock becomes slightly longer than 24 hrs. The 24 hr cycle
of light detection allows to entrain the clock to maintain a 24 hr cycle.
Review
Absorption and transport
Osmosis and hydrostatic pressure used?
(3) Hydrostatic
pressure in
cells
PROTOPLAST
SOLUTION
Concentration
0.3 molar
Pressure
0 megapascals
Concentration
0.3 molar
(Isotonic)
Concentration
0.27 molar
Pressure
0.66 megapascals
Turgor pressure is one
type of hydrostatic
pressure. Turgor
pressure is the result of
a combination of
osmosis and cell wall
rigidity.
Fig. 3-7 (a-c), p. 36
Concentration
0 molar
(Hypotonic)
Concentration
0.5 molar
Pressure
0 megapascals
Concentration
0.5 molar
(Hypertonic)
LIGHT
Events leading to
the opening of a
stoma:
The production of
malate and the
influx of K+ and Clpowered by the
electrical and pH
gradients produced
by the proton pump
increase the
concentration of
osmotically active
solutes in the guard
cells. As a result,
water flows into the
cells by osmosis.
starch
malic acid
malate–
plasma
membrane
ATP
H+
ADP
+ Pi
proton
pump

H+
+
K+
CI
H+
K+
CI
Fig. 11-8a, p. 170
Root pressure is generated by an osmotic pump
After passing the endodermis, mineral
nutrients accumulate in the stele of the
root. The endodermal cells provide the
differentially permeable membrane
needed for osmosis.
•Soil saturated with water
–Water tends to enter root and stele
–Builds up root pressure in xylem
–Forces xylem sap up into shoot
Fig. 11-13a, p. 178
Mechanism of Phloem Transport
high
pressure
low
pressure
sieve tube
sucrose
sucrose
H2O
H2O
sucrose
glucose
sucrose
H2O
glucose H2O
H2O
source
sink
sucrose
CO2 + H2O
parenchyma
H2O
Fig. 11-14, p. 179
parenchyma
Sucrose is actively transported into the sieve tubes at the food source region of the
plant (leaves or storage organs) and removed at the sink regions (regions of growth or
storage). Water follows by osmosis, increasing the hydrostatic pressure in the sieve
tubes at the source region and decreasing the pressure at the sink region. The sievetube contents flow en masse from high(source)- to low(sink)-pressure regions.
Absorption and transport
Water flow through xylem compared to phloem?
What are the similarities, what are the
differences?
Absorption and transport
Do plants acidify the soil they grow in?
Yes:
- Respiration
- H+ extrusion
Soil Formation
atmospheric gases:
CO2
SO2
N2O5
rock
acids:
H2CO3
H2SO3
HNO3
rain
wind and water
erode rocks
and soil
freeze-thaw
produces cracks
roots: crack rocks through
pressure, secrete acid
Fig. 11-11, p. 175
Active Uptake of Minerals
Into Root Cells
Fig. 11-12, p. 177
Differential Growth
• What is the link between turgor pressure, cell
walls and differential growth?
(3) Hydrostatic
pressure in
cells
PROTOPLAST
SOLUTION
Concentration
0.3 molar
Pressure
0 megapascals
Concentration
0.3 molar
(Isotonic)
Concentration
0.27 molar
Pressure
0.66 megapascals
Turgor pressure is one
type of hydrostatic
pressure. Turgor
pressure is the result of
a combination of
osmosis and cell wall
rigidity.
Fig. 3-7 (a-c), p. 36
Concentration
0 molar
(Hypotonic)
Concentration
0.5 molar
Pressure
0 megapascals
Concentration
0.5 molar
(Hypertonic)
Differential growth
a
b
Rate of cell elongation is
higher on the a-side of
the coleoptile compared
to the b-side. This leads
to differential growth:
increased growth rate on
one side of plant organ,
results in curvature of the
organ.
Plant transformation
Agrobacterium
Auxin
Cytokinin
Dedifferentiation
Differentiation
Transforming a plant cell by
using Agrobacterium
Gene to be introduced in plant
cell (for example: a gene that
encodes the Luciferase protein)
Plant Cell
+
Agrobacterium
Modified
Nucleus
Ti-plasmid
Transformed
Plant Cell
Agrobacterium
Plant cell makes
luciferase protein
auxin
cytokinin
Major signals that control plant
growth and development
• Internal signals: Plant Hormones
- AUXIN
- CYTOKININ
- ETHYLENE
- ABSCISIC ACID
- GIBBERELLIC ACID
The plant’s toolbox for positive and negative
control of physiological and developmental
processes.
Shade avoidance
Shading of a plant by plants that grow above it
leads to increased or decreased Phy activity ?
Absorption spectra of Chlorophyll a and b
Percent of light absorbed
100
chlorophyll b
80
60
chlorophyll a
40
20
0
400
500
Fig. 10-5, p. 152
600
700
Wavelength (nm)
660
730
The ratio of Red (660 nm) to Far Red (730 nm) light will be low underneath green
leaves that absorb light between 640 and 700 nm.
The predicted properties of the receptor
The End