Post on 29-Dec-2015
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Group Reading Discussion 1
• Please read before Thursdays lecture • Exercise will be given out and will discuss at end of
Thursdays lecture • Group submit on Tuesday next week.
Membranes
http://search.ebscohost.com/login.aspx?direct=true&db=a9h&AN=31223131&site=ehost-live
Read this
Figure accompanying Discussion paper
From: Kiang et al. (2007) Spectral Signatures of Photosynthesis. II. Find it here, but I’m not suggesting that you read it: http://online.liebertpub.com/doi/pdf/10.1089/ast.2006.0108
FYI
Salvia’s and aridity adaptations
Thick hairy
Thin smooth leaf
Thick white hairs leathery
Intermediate thickness small
Membranes
Talent® Red Shades Gazania rigens http://www.benary.com/en/product/M4120
Leaf adaption
Leaf hairs Dissected leaves
Gazania rigens
• High light, dry, sporadic rainfall • Leaf hairs:
– Reduce UV load on photo’ cells – But increase leaf temperature (not
much)
• Dissected leaves: – Entire leaves when well watered – Dissected leaves when droughted
• Increases coupling with atmosphere, thus leaves are cooler.
Membranes
http://www.sciencedirect.com/science/article/pii/S0176161799801436#
Membranes
Weed flowers White to reflect as much light and heat as possible Datura – transpires to reduce temperature Convolvulus – follows sun to have hot flowers?
Govil (1971) Morphological studies in the family Convolvulaceae
Rodrigues (2000) Flower anatomy and morphology of Exodeconus
Membranes
From: Dacey (1980) Internal winds in water lilies
Water lily petioles
http://www.sciencemag.org/content/210/4473/1017.short
From: Richards et al. (2012). Amer. J. Bot 94
FYI
Arctotheca populifolia
Membranes
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
A. populifoliaH. cordata
D.suffructicosumI. pes-caprae
G. rigensS. plumieri
S. primulifloraS. plumosaS. elegans
P. rigidaM. cordifolia
C. obtusifoliumR. caribaeR. digitata
C. moniliferaC. deliciosusH.cymosumM. muricataS. argentea
R. crenataA. cyclopsB. discolor
M. caffraA. natalensis
Stem tissue density (g cm-3)
Unburied Partially buried
Mobile-dunespecies
Stable-dunespeciesClimbing
species
n.s.n.s.
n.s.
***
***
***
**n.s.
n.s.
n.s.
**
Fore
stB
each
Ord
er o
f occ
urre
nce
on d
une
zona
tion
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
A. populifoliaH. cordata
D.suffructicosumI. pes-caprae
G. rigensS. plumieri
S. primulifloraS. plumosaS. elegans
P. rigidaM. cordifolia
C. obtusifoliumR. caribaeR. digitata
C. moniliferaC. deliciosusH.cymosumM. muricataS. argentea
R. crenataA. cyclopsB. discolor
M. caffraA. natalensis
Stem tissue density (g cm-3)
Unburied Partially buried
Mobile-dunespecies
Stable-dunespeciesClimbing
species
n.s.n.s.
n.s.
***
***
***
**n.s.
n.s.
n.s.
**
Fore
stB
each
Ord
er o
f occ
urre
nce
on d
une
zona
tion
Membranes
Membranes
• Importance • Structure • Fluid Mosaic Model • Extrinsic Factors
Affecting Membranes
http://upload.wikimedia.org/
Membranes
Membranes
• Membranes found in plants – Plasma membrane = plasmalemma – Chloroplast (plastid) membranes
• Outer and inner (double) • Thylakoid
– Mitochondrion membrane (double) – Nuclear membrane – Vacuole membrane = tonoplast – Microbodies
• Peroxysomes, glyoxysomes
http://en.wikipedia.org/wiki/Lipid_bilayer Great explanation:
http://plantsinaction.science.uq.edu.au
Great online textbook:
Read some of this
Read this
Membranes
Importance of Membranes
• Interface for plant-environment interactions – “Line” between “inside” and “outside” – Provide ability to “sense” changes in environment
• Changes in membrane composition/configuration
– Membranes are dynamic systems and are constantly in a state of change
Membranes
Importance of Membranes • Most biological membranes are similar, regardless of the kind of cell
or organism in which they are found • Allows cell to take up, exclude and/or retain surrounding substances • Rate-limiting step for the movement of molecules into and out of
plant cells • Site of action for plant growth substances
Membranes
Structure
• Lipid bilayer – Polarity
• Polar head – Phosphate
• Non-polar tail – Lipids (fatty acids)
– Amphipathic – both water and fat loving
http://courses.cm.utexas.edu/jrobertus/ http://www.phschool.com/
Membranes
Structure • Lipids
– Phospholipids – most membranes – Glycolipids – chloroplast membranes (no P)
• Glycosylglycerides – polar = galactose etc.
Membranes
Structure • Lipids
– Degree of saturation • Less saturation = more fluidity
– Phytosterols • Main function
– Stability at higher temperatures » Example – Cholesterol in animals
Cholesterol
Membranes
Structure • Proteins (~50% of membrane)
– Integral or intrinsic proteins - ion channels and signal transduction
– Peripheral or extrinsic proteins – Anchored proteins - with a fatty acid
Membranes
Structure
• Proteins – Integral or intrinsic proteins
• Membrane function – Catalytic
» Use energy to pump ions across membrane (e.g., Na+:K+ pump) » Movement is against concentration gradient
– Channels » K+
– Carriers » Sucrose
Membranes
Structure
• Peripheral or extrinsic proteins – Recognition functions
• Bacterial, fungal diseases • Recognition = resistance or tolerance • Rhizobium “infection” • Pollen-stigma interactions • Graft incompatibilities
http://www.slic2.wsu.edu:82/hurlbert/micro101/
A Model for the Brassica self incompatability (SI) Reaction.The SI response occurs within the stigmatic papilla cells.
Franklin-Tong V E , and Franklin F C H Plant Cell 2000;12:305-308
©2000 by American Society of Plant Biologists
PCP = pollen coat protein SCR = pollen S ligand SRK = S receptor kinase SLG = S locus glycoprotein (unknown function) Model: 1) Pollen lands 2) PCP and SCR flow between pollen
and stigma 3) SCR approaches SRK 4) If SCR is allelic with SRK then
incompatible reaction is triggered 5) SRK external part of protein triggers internal response of its intracellular domain a protein kinase 6) Possibly aquaporin gated to prevent water flow to pollen
Membranes
Fluid Mosaic Model
• Sidedness – Due to the differences in proteins and lipids
on each side and amphipathic nature of lipids (molecule to possess both hydrophilic and hydrophobic characteristics) phospholipid bilayer containing proteins
– Structural analysis • Freeze-fracture techniques
Membranes
Fluid Mosaic Model
• Sidedness – Freeze-fracture analysis
https://wikispaces.psu.edu/display/Biol230
Membranes
Extrinsic Factors Affecting Membrane Fluidity
• Temperature effects – Change in structure
• Ability of plant to tolerate extremes based in ability to alter membrane structure and composition
Effect of Temperature on Plant Membranes
• Beetroots exposed to varying temperatures – Color assay
Membranes
http://vcebiology.edublogs.org/2010/03/11/effect-of-temperature-on-plasma-membranes/
0oC 20oC 50oC 70oC
Effect of Temperature on Plant Membranes
• Temperature effect on chloroplast membranes – Chlorophyll fluorescence
Membranes
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
32 37 42 47 52
Phot
osyn
thes
is e
ffic
ienc
y (F
luor
esce
nce)
Leaf temperature (oC)
0.8 no stress
Membranes
Membrane Lipid Saturation • Saturated
– Better in high temps • Unsaturated
– Better in low temps • Transgenic Arabidopsis
– Silenced a gene (enzyme) that saturates chloroplast membrane fatty acids
• Therefore, more fatty acids like this: C-C-C-C • Plants better able to acclimate to higher temperatures
http://biology.clc.uc.edu/
margarine
Membranes
Extrinsic Factors Affecting Membrane Fluidity
• Temperature effects – Change in structure
• Chilling sensitivity correlated with degree of saturation of lipids
http://edis.ifas.ufl.edu/
Leads to chilling injury
Membranes
Extrinsic Factors Affecting Membrane Function
• Hydration – If cell water percentage <20% DM, then
membrane breaks down • Ionic interactions and membrane fluidity
– Ca2+ and Mg2+
• Ca2+ makes membrane more rigid, gel-like
Photosynthesis: Light-dependent Reactions
Photosynthesis
• Overview – Importance of photosynthesis – Importance of water – Whole-plant perspective: Important trade-off – Path of CO2
• Light-dependent Reactions – Chloroplasts, thylakoids and chlorophyll – Light-dependent reactions – Electron Transport Chain (Z-Scheme)
Photosynthesis
• Light-dependent – Old jargon = light reactions
• Light-independent – Old jargon = dark reactions
• Problem: “dark” reactions also taking place in the light
Photosynthesis: Light-dependent Reactions
Photosynthesis: Light-dependent Reactions
Photosynthesis
• In photosynthesis, plants absorb light energy from the sun and convert it to chemical energy stored in glucose and other carbohydrates and in the process release oxygen.
Photosynthesis: Light-dependent Reactions
Importance of Photosynthesis
• Source of atmospheric oxygen • Source of energy for food chain • Direct/indirect involvement in all products • Maintaining a stable ecosystem
http://www.greenseat.com
Photosynthesis: Light-dependent Reactions
Importance of Photosynthesis
• Source of atmospheric oxygen
http://www.snowballearth.org/
Photosynthesis: Light-dependent Reactions
Importance of Photosynthesis
• Source of atmospheric oxygen – Oxygen is evolved as a by-product of
photosynthesis – Oxygen originates from water – Plant and animals use O2 during respiration
and evolve CO2
– Only photosynthetic organisms can use CO2 for photosynthesis and evolve O2
Photosynthesis: Light-dependent Reactions
Importance of Photosynthesis
• Source of energy for food chain
http://pack152.net/
Photosynthesis: Light-dependent Reactions
Importance of Photosynthesis
• Source of energy for food chain – Plants are photoautotrophs
• Produce their own food by photosynthesis using light energy
– Everything after plants are heterotrophs • Feed on something else
Photosynthesis: Light-dependent Reactions
Importance of Photosynthesis
• Direct/Indirect involvement in all products – Almost everything around us has a direct or indirect origin in the
photosynthetic process • Food • Wood • Oil
– Plastics • Fibers
– Clothing – Paper – Money
• Drugs • You are what you eat! (see two lectures time)
Photosynthesis: Light-dependent Reactions
Importance of Photosynthesis
• Maintaining a Stable Ecosystem - Carbon Cycle – Plants convert CO2 in the atmosphere into
carbohydrates used for the growth of the plant. Ultimately this carbon may be found in:
• Oil, coal, peat • Non-green plants (parasites/saprophytes) feeding on green
plants • Animals that feed on green plants
– Finally, the carbon will return to the atmosphere as CO2 through respiration, combustion or decay
Diffusion
• Statistical tendency for equalization of different concentrations of molecules
• Due to random thermal movement of molecules – therefore temperature responsive
Membranes
http://en.wikipedia.org/wiki/File:Diffusion.svg
Diffusion
Membranes
Time to reach half = distance2
2.8*Diffusivity
+Temperature -molecular weight -nonlinear (proteins) -interactions with other molecules
Diffusivity (m2 s-1)
Distance Time for B to reach half conc. at A
H2O in air 2.42x10-5 1m 4 hours CO2 in air 1.51x10-5 1m 6 hours CO2 in water 1.7x10-9 1m 6.7 units? CO2 in water 1.7x10-9 20µm (a cell) 0.1 second CO2 across membrane 1x10-12? 20µm (a cell) 143 seconds Sucrose in water 0.52x10-9 20µm (a cell) 0.3 second
A B distance
Photosynthesis: Light-dependent Reactions
Whole Plant Perspective • Photosynthesis and
Transpiration – CO2 enters leaf through
open stomates and water vapor is lost (evaporation, transpiration)
• Important trade-off for the plant’s physiology
– CO2 converted to carbohydrate (photosynthate) in the leaf and transported throughout the plant via the phloem
– Water is taken up by roots and transported via the xylem to the leaves
Photosynthesis: Light-dependent Reactions
Leaf Cross-Section
• Cuticle – Covers surfaces of leaf – Conserves water
• Epidermis – Beneath cuticle – Contains stomates (mostly
on lower epidermis)
• Palisade and Spongy Parenchyma – Between upper and lower
epidermis – Photosynthetic tissue
http://www.osmotek.com
Photosynthesis: Light-dependent Reactions
Chloroplasts • Photosynthesis takes
place in chloroplasts – Surrounded by 2 smooth
membranes – Control transport in/out of
chloroplasts
• Inner thylakoid membrane system – Grana = stacks of
thylakoids • Contain photosynthetic
pigments, chlorophyll and carotenoids
• Site of light-dependent reactions
http://photoprotection.clinuvel.com/
Photosynthesis: Light-dependent Reactions
Chloroplasts • Stroma
– Liquid matrix – Site of light-
independent reactions (CO2 conversion)
How does CO2 get to the sites of photosynthesis? i.e. from intercellular airspace to Rubisco in the chloroplast stroma
Photosynthesis: Light-dependent Reactions
Evans et al. (2009)
Step 2: Plasma membrane
H2O
H2O
H2O
H2O H2O
H2O
H2O H2O
H2O
CO2
CO2
H2O
H2O CO2 CO2
Through lipid bilayer, “aqua”porins (cooporins) or both? n.b. membranes are ~50% protein
From: Wang et al. (2006)
Step 2: Plasma membrane - Aquaporins form tetramers (four water pores) - With the possibility of a fifth pore that CO2 may transit - Aquaporins are passive, only changing the permeability of a membrane not transporting molecules
Step 3: cytosol
Evans et al. (2009)
- Chloroplast alignment with plasma membrane minimizes distance of diffusion - Carbonic anhydrase scavenges CO2 forming HCO3- thus increasing the gradient over the plasma membrane - carbonic anhydrase 106 reactions per second uses Zn in enzyme
Why is the diffusion of CO2 in the leaf important?
• We rely on photosynthesis, but don’t understand it • These steps result in up to a 50% limitation on
photosynthesis – potential for increasing crop yields • There appears to be no tradeoff – changing it won’t affect
water use or nitrogen, Or will it? We don’t know!
Photosynthesis: Light-dependent Reactions
Photosynthesis: Light-dependent Reactions
Water and Photosynthesis
• Stabilizes plant temperature • Maintains plant’s turgor • Dissolves minerals in the soil/transport • Driving force for phloem (sugar)
translocation • Splits into protons (H+), electrons (e-) and
oxygen (O2)
Photosynthesis: Light-dependent Reactions
Three Processes in Photosynthesis
• Absorption of light energy – Pigments in thylakoids
• Light-dependent Reactions – Pigments and proteins in thylakoids – Generates ATP and NADPH
• Light-independent (dark) Reactions – Enzymes in stroma – Reduce CO2 to carbohydrates using ATP and
NADPH
Photosynthesis: Light-dependent Reactions
Stage of Photosynthesis
• Two stages of photosynthesis
Light-dependent Reactions
Light-independent Reactions
Anatomy, Structure and Function http://en.wikipedia.org/wiki/File:Common_lipids_lmaps.png