The Dual Role of Sunlight: Energy and Information
1
6 The Dual Role of Sunlight: Energy and Information Lectured by L-F Chien
2
Sunlight •Sunlight is a source of energy which drives photosynthesis. •Sunlight is a source of information for plants that drives phenomena such as photomorphogenesis and photoperiodism.
3
The principle topics to be covered: •explore the physical nature of light and how light interacts with matter • discuss some of the terminology used in describing light and methods for measuring it • discuss briefly the characteristics of light in the natural environment of plants • reviews the principal pigments and pigment systems found in plants
6.1 The physical nature of light 6.1.1 Light is electromagnetic energy, which exists in two forms •The electromagnetic spectrum (wavelength)
Figure 6.1
4
5
•The electromagnetic spectrum c λv
(Taiz & Zeigher 2006)
6
6.1.2 Light can be characterized as a wave phenomenon •Light has properties of both particles and waves. –The wave properties can be characterized in terms of the wavelength and frequency. c v
–The frequency (n) is the number of wave crests per second. –The wavelength (l) is the distance between crests of the wave. –The speed of light is c.
7
8
Wave nature of light
(electric field) (magnetic field)
Figure 6.1
c v c E q h hv λ
c, light speed: 3108 m s1 [lambda], wavelength: nanometer (nm) [nu], frequency: Hertz (Hz) or wavenumber (cm1) Eq, energy: Joule (J) or calorie (cal) h,Pl anck’ sconst ant :6. 6261034 J sec
9
Quantum energy (Eq) •The energy (Eq) of a particular photon is called a quantum and is related to the wavelength and frequency. c
─red light of 660 nm Eq ( red light) hv h λ 3 10 10 cm sec -1 (6.626 10 J sec)( ) 660 nm 10 23 molecules 6.023 -19 -1 301 10 J ] photon [ N mol -1 181 kJ mol 34
─blue light of 435 nm Eq ( blue
hv h light)
c λ
3 10 10 cm sec -1 (6.626 10 J sec)( ) 435 nm 10 23 molecules 6.023 -19 -1 301 10 J ] photon [ N mol -1 274 kJ mol 34
10
6.1.4 Light energy can interact with matter •Absorbed light can induce photochemical reactions according to the Gotthaus-Draper principle. •A molecule that absorbs light is a pigment.
(Taiz & Zeigher 2006)
11
The absorption light by pigment molecules Figure 6.3
?
?
?
12
Molecular orbital of H2 H2
(Chang 2000)
13
Molecular orbital of CO CO
(Chang 2000)
14
T? S?
Molecular electronic state (ES) 1 2( s)
15
where s represents electron spin of +½ or ½
(½)
(+½) or
(+½) (½)
ES of Chl =1+2[(+½)+(½)] =1 (Singlet state) 1Chl
S0: singlet ground-state
(+½)
ES of Chl* =1+2[(+½)+(½)] =1 (Singlet state) 1Chl*
S1: singlet first excited-state
(+½) ES of Chl* =1+2[(+½)+(+½)] =3 (Triplet state) 3Chl*
T1: triplet first excited-state
16
Light absorption: (i) 1Chl + hv 1Chl* (ii) 1Chl + hv 1Chl*
1Chl*
Blue
ns=10-9
60 Integral area no. of molecules
Thermal deactivation (relax)
1Chl*
Red
40
Fluorescence fs=10-15 1Chl
100
Fluorescence Phosphorescence
6.1.5 How does one illustrate the efficiency of light absorption ant its physiological effects? •Action spectrum Figure 6.3
leaf photosynthesis
absorption spectrum of Chl a
spectrum, s. spectra, pl.
17
6.1.6 Accurate measurement of light is important in photobiology •Three parameters are relevant to the measurement of light. –Light quantity –Light quality, spectral composition, or spectral energy distribution (SED) –Timing and duration of light treatment
18
Concepts and units for measuring light
(Taiz & Zeiger 2006)
19
20
Flat and spherical light sensors
Flat
Spherical
(Taiz & Zeiger 2006)
21
Light can be measured omnidirectionally (from all directions) as fluence rate. Units: (1) energy fluence rate: (a) watts per square meter (W m2) (b) Joules per square meter per second (J m2 s1) [1 W = 1 J s1] (2) photon fluence rate: mol m2 s1
22
Light can be measured as energy, and the amount of energy that falls on a flat sensor of known area per unit time is quantified as irradiance. Units: watts per square meter (W m2) PAR: photosynthetically active radiation
23
Light can be measured as the number of incident quanta (quantum, s.; quanta, pl.). Unit: (a) moles per square meter per second (mol m2 s1) (b) microEinstein (Einstein, one mole of photons) per square meter per second (E m2 s1) PPFD: photosynthetic photon flux density
24
Spectral energy distribution of sunlight (1) Figure 6.5A
紅外光 紫外光
25
Spectral energy distribution of sunlight (2) Figure 6.5B
白熾光
6.2 The natural radiation environment
(A) Radiation from the sun (B) Earth reradiates infrared (heat) back (C) Infrared radiation either reflected back to earth or absorbed by atmospheric gases
Figure 6.6
26
27
6.3 Photoreceptors absorb light for use in a physiological process •Photoreceptors are pigment molecules that absorb and process light into a form that can be used by the plant. •Photoreceptors can be chromoproteins, consisting of a pigment (chromophore) and a catalytic protein (apoprotein).
28
Photopigments: (1) Chlorophylls:
chlorophylls a, b, c, d bacteriochlorophyll a, b
(2) Phycobilins:
phycoerythrobilin (PE) phycocyanobilin (PC) allophycocyanin (AP)
(3) Carotenoids:
(about 700 compounds) -carotene lutein xanthophyll cycle pigments
6.3.1 Chlorophylls are primarily responsible for harvesting light energy for photosynthesis •Chlorophylls: (a)chlorophylls: chlorophylls a, b, c, d, (b) bacteriochlorophylls: bacteriochlorophyll a, b
29
Chemical structure of chlorophylls
30
(chlorophyll, Greek: chloros = green + phyllon =leaf)
Figure 6.7 Porphyrin
Phytol (5-carbon isoprene, lipid-soluble)
Phyeophytin: no Mg 2+
31
Chlorophylls
Chlorophyll a, c
Chlorophyll d
Chlorophyll b
32
Absorption spectra of Chl a and Chl b
Figure 6.8
6.3.2 Phycobilins serve as accessory lightharvesting pigments in red algae and cyanobacteria •Phycobilins: (a) phycobilins: ─phyco, algal origin ─pr ot ei ns
(i) phycoerythrobilin (PE) (ii) phycocyanobilin (PC) (iii) allophycocyanin (AP) (b) phycobilinsomes: ─l ar gemacr omol ecul arcompl ex es
(c) phytochrome: ─Pr ,Pf r
33
34
Open-chain tetrapyrrole chromophore of phycocyanin Figure 6.9
(water-soluble)
Absorption spectra of phycocyanin and phycoerythrin Figure 6.9 phycoerythrin
phycocyanin
35
6.3.3 Carotenoids account for the autumn colors •Carotenoids: ─about700compounds ─C40 terpenoids ─accessory pigments ─in chloroplast membrane or chromoplasts
(a) carotenes: a, , g-carotene lutein (b) xanthophyll cycle pigments
36
Carotenes and xanthophylls Figure 6.11
37
Absorption spectra of a-carotene and -carotene
38
b-carotene
a-carotene
Figure 6.12
39
Absorption spectra of some photosynthetic pigments Chlb
Chla
PE
BChla
Chla
BChla
-Car Chlb
(Taiz & Zeiger 2006)
6.3.4 Cryptochorome and photoropin are photoreceptors sensitive to blue light and UV-A radiation •Cryptochrome [隱花色素] –Gr., hidden colour
–blue light/UV-A photoreceptor –Arabidopsis CRY1 and CRY 2 genes –CRY1 protein, a flavoprotein containing FAD and pterin, 75kDa –using blue light to stimulate repair of UV-induced damage to microbial DNA
–regulate germination, photoperiodism
40
6.3.4 Cryptochorome and photoropin are photoreceptors sensitive to blue light and UV-A radiation •Phototropins (PHOT) –blue light photoreceptor –Arabidopsis PHOT1 and PHOT2 genes –PHOT1 protein, a flavoprotein containing 2 FMN, 120 kDa –In optimizing photosynthetic efficiency
41
6.3.6 Flavonoids provide the myriad flower colors and act as a natural sunscreen Phenylpropane
Riboflavin
C6-C3-C6
Figure 6.14
Pterin Figure 6.13
42
Absorption spectrum of the anthocyanin, pelargonin
Figure 6.15 pelargonin (天竺葵花紅素)
43
44
Assay Chapter Review: 1, 2, 3, 6 (p-107) Deadline: next Thursday Delay: 100n2
6 The Dual Role of Sunlight: Energy and Information Lectured by L-F Chien
2
Sunlight •Sunlight is a source of energy which drives photosynthesis. •Sunlight is a source of information for plants that drives phenomena such as photomorphogenesis and photoperiodism.
3
The principle topics to be covered: •explore the physical nature of light and how light interacts with matter • discuss some of the terminology used in describing light and methods for measuring it • discuss briefly the characteristics of light in the natural environment of plants • reviews the principal pigments and pigment systems found in plants
6.1 The physical nature of light 6.1.1 Light is electromagnetic energy, which exists in two forms •The electromagnetic spectrum (wavelength)
Figure 6.1
4
5
•The electromagnetic spectrum c λv
(Taiz & Zeigher 2006)
6
6.1.2 Light can be characterized as a wave phenomenon •Light has properties of both particles and waves. –The wave properties can be characterized in terms of the wavelength and frequency. c v
–The frequency (n) is the number of wave crests per second. –The wavelength (l) is the distance between crests of the wave. –The speed of light is c.
7
8
Wave nature of light
(electric field) (magnetic field)
Figure 6.1
c v c E q h hv λ
c, light speed: 3108 m s1 [lambda], wavelength: nanometer (nm) [nu], frequency: Hertz (Hz) or wavenumber (cm1) Eq, energy: Joule (J) or calorie (cal) h,Pl anck’ sconst ant :6. 6261034 J sec
9
Quantum energy (Eq) •The energy (Eq) of a particular photon is called a quantum and is related to the wavelength and frequency. c
─red light of 660 nm Eq ( red light) hv h λ 3 10 10 cm sec -1 (6.626 10 J sec)( ) 660 nm 10 23 molecules 6.023 -19 -1 301 10 J ] photon [ N mol -1 181 kJ mol 34
─blue light of 435 nm Eq ( blue
hv h light)
c λ
3 10 10 cm sec -1 (6.626 10 J sec)( ) 435 nm 10 23 molecules 6.023 -19 -1 301 10 J ] photon [ N mol -1 274 kJ mol 34
10
6.1.4 Light energy can interact with matter •Absorbed light can induce photochemical reactions according to the Gotthaus-Draper principle. •A molecule that absorbs light is a pigment.
(Taiz & Zeigher 2006)
11
The absorption light by pigment molecules Figure 6.3
?
?
?
12
Molecular orbital of H2 H2
(Chang 2000)
13
Molecular orbital of CO CO
(Chang 2000)
14
T? S?
Molecular electronic state (ES) 1 2( s)
15
where s represents electron spin of +½ or ½
(½)
(+½) or
(+½) (½)
ES of Chl =1+2[(+½)+(½)] =1 (Singlet state) 1Chl
S0: singlet ground-state
(+½)
ES of Chl* =1+2[(+½)+(½)] =1 (Singlet state) 1Chl*
S1: singlet first excited-state
(+½) ES of Chl* =1+2[(+½)+(+½)] =3 (Triplet state) 3Chl*
T1: triplet first excited-state
16
Light absorption: (i) 1Chl + hv 1Chl* (ii) 1Chl + hv 1Chl*
1Chl*
Blue
ns=10-9
60 Integral area no. of molecules
Thermal deactivation (relax)
1Chl*
Red
40
Fluorescence fs=10-15 1Chl
100
Fluorescence Phosphorescence
6.1.5 How does one illustrate the efficiency of light absorption ant its physiological effects? •Action spectrum Figure 6.3
leaf photosynthesis
absorption spectrum of Chl a
spectrum, s. spectra, pl.
17
6.1.6 Accurate measurement of light is important in photobiology •Three parameters are relevant to the measurement of light. –Light quantity –Light quality, spectral composition, or spectral energy distribution (SED) –Timing and duration of light treatment
18
Concepts and units for measuring light
(Taiz & Zeiger 2006)
19
20
Flat and spherical light sensors
Flat
Spherical
(Taiz & Zeiger 2006)
21
Light can be measured omnidirectionally (from all directions) as fluence rate. Units: (1) energy fluence rate: (a) watts per square meter (W m2) (b) Joules per square meter per second (J m2 s1) [1 W = 1 J s1] (2) photon fluence rate: mol m2 s1
22
Light can be measured as energy, and the amount of energy that falls on a flat sensor of known area per unit time is quantified as irradiance. Units: watts per square meter (W m2) PAR: photosynthetically active radiation
23
Light can be measured as the number of incident quanta (quantum, s.; quanta, pl.). Unit: (a) moles per square meter per second (mol m2 s1) (b) microEinstein (Einstein, one mole of photons) per square meter per second (E m2 s1) PPFD: photosynthetic photon flux density
24
Spectral energy distribution of sunlight (1) Figure 6.5A
紅外光 紫外光
25
Spectral energy distribution of sunlight (2) Figure 6.5B
白熾光
6.2 The natural radiation environment
(A) Radiation from the sun (B) Earth reradiates infrared (heat) back (C) Infrared radiation either reflected back to earth or absorbed by atmospheric gases
Figure 6.6
26
27
6.3 Photoreceptors absorb light for use in a physiological process •Photoreceptors are pigment molecules that absorb and process light into a form that can be used by the plant. •Photoreceptors can be chromoproteins, consisting of a pigment (chromophore) and a catalytic protein (apoprotein).
28
Photopigments: (1) Chlorophylls:
chlorophylls a, b, c, d bacteriochlorophyll a, b
(2) Phycobilins:
phycoerythrobilin (PE) phycocyanobilin (PC) allophycocyanin (AP)
(3) Carotenoids:
(about 700 compounds) -carotene lutein xanthophyll cycle pigments
6.3.1 Chlorophylls are primarily responsible for harvesting light energy for photosynthesis •Chlorophylls: (a)chlorophylls: chlorophylls a, b, c, d, (b) bacteriochlorophylls: bacteriochlorophyll a, b
29
Chemical structure of chlorophylls
30
(chlorophyll, Greek: chloros = green + phyllon =leaf)
Figure 6.7 Porphyrin
Phytol (5-carbon isoprene, lipid-soluble)
Phyeophytin: no Mg 2+
31
Chlorophylls
Chlorophyll a, c
Chlorophyll d
Chlorophyll b
32
Absorption spectra of Chl a and Chl b
Figure 6.8
6.3.2 Phycobilins serve as accessory lightharvesting pigments in red algae and cyanobacteria •Phycobilins: (a) phycobilins: ─phyco, algal origin ─pr ot ei ns
(i) phycoerythrobilin (PE) (ii) phycocyanobilin (PC) (iii) allophycocyanin (AP) (b) phycobilinsomes: ─l ar gemacr omol ecul arcompl ex es
(c) phytochrome: ─Pr ,Pf r
33
34
Open-chain tetrapyrrole chromophore of phycocyanin Figure 6.9
(water-soluble)
Absorption spectra of phycocyanin and phycoerythrin Figure 6.9 phycoerythrin
phycocyanin
35
6.3.3 Carotenoids account for the autumn colors •Carotenoids: ─about700compounds ─C40 terpenoids ─accessory pigments ─in chloroplast membrane or chromoplasts
(a) carotenes: a, , g-carotene lutein (b) xanthophyll cycle pigments
36
Carotenes and xanthophylls Figure 6.11
37
Absorption spectra of a-carotene and -carotene
38
b-carotene
a-carotene
Figure 6.12
39
Absorption spectra of some photosynthetic pigments Chlb
Chla
PE
BChla
Chla
BChla
-Car Chlb
(Taiz & Zeiger 2006)
6.3.4 Cryptochorome and photoropin are photoreceptors sensitive to blue light and UV-A radiation •Cryptochrome [隱花色素] –Gr., hidden colour
–blue light/UV-A photoreceptor –Arabidopsis CRY1 and CRY 2 genes –CRY1 protein, a flavoprotein containing FAD and pterin, 75kDa –using blue light to stimulate repair of UV-induced damage to microbial DNA
–regulate germination, photoperiodism
40
6.3.4 Cryptochorome and photoropin are photoreceptors sensitive to blue light and UV-A radiation •Phototropins (PHOT) –blue light photoreceptor –Arabidopsis PHOT1 and PHOT2 genes –PHOT1 protein, a flavoprotein containing 2 FMN, 120 kDa –In optimizing photosynthetic efficiency
41
6.3.6 Flavonoids provide the myriad flower colors and act as a natural sunscreen Phenylpropane
Riboflavin
C6-C3-C6
Figure 6.14
Pterin Figure 6.13
42
Absorption spectrum of the anthocyanin, pelargonin
Figure 6.15 pelargonin (天竺葵花紅素)
43
44
Assay Chapter Review: 1, 2, 3, 6 (p-107) Deadline: next Thursday Delay: 100n2
