Lec 4 Membranes

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

http://online.liebertpub.com/doi/pdf/10.1089/ast.2006.0108

http://online.liebertpub.com/doi/pdf/10.1089/ast.2006.0108

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

http://www.benary.com/en/product/M4120

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#

http://www.sciencedirect.com/science/article/pii/S0176161799801436

http://www.sciencedirect.com/science/article/pii/S0176161799801436

Membranes

Weed flowers

Convolvulus arvensis Datura wrightii

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

http://www.sciencemag.org/content/210/4473/1017.short

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

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f occ

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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

Presenter

Presentation Notes

Stem density: 0.1 g dry matter cm-3 That’s 90% water! The stem is parenchyma and vascular bundles The stem wilts

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

http://en.wikipedia.org/wiki/Lipid_bilayer

http://plantsinaction.science.uq.edu.au/

http://plantsinaction.science.uq.edu.au/

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

Quan

Sticky Note

Helps maintain differences in compartments by selectively allowing things to enter or exit compartment Receives signals from environment and transduces them to inside Plays a major role in establishing cell migration and association Hydrophobic interior is exclusive site for some reactions Gives identity to cell Forms boundaries to separate environments from one another

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.

Quan

Sticky Note

glycosyl glyceride: A class of glycolipids structurally analogous to phospholipids; they are the major glycolipids of plants and microorganisms but are rare in animals.

Quan

Sticky Note

Glycolipids are lipids with a carbohydrate attached. Their role is to provide energy and also serve as markers for cellular recognition.

Membranes

Structure • Lipids

– Degree of saturation • Less saturation = more fluidity

– Phytosterols • Main function

– Stability at higher temperatures » Example – Cholesterol in animals

Cholesterol

Quan

Sticky Note

Phytosterols, which encompass plant sterols and stanols, are steroid compounds similar to cholesterol which occur in plants and vary only in carbon side chains and/or presence or absence of a double bond.

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

Presenter

Presentation Notes

A Model for the Brassica SI Reaction.The SI response occurs within the stigmatic papilla cells. When a pollen grain alights on the papilla surface, the pollen coat, containing pollen coat proteins such as PCPs (black trapezoids) and the recently identified pollen S ligand, SCR (black circles), flows to form a layer (shown in light gray) between the pollen and stigma. If, as shown in this case, the SCR carried within this coating is allelic with the recipient stigma, an incompatible reaction is triggered. S allele–specific recognition of SCR by the extracellular region of the S receptor kinase (SRK) results in activation of its intracellular Ser-Thr protein kinase domain (shown as a black star). Although the role of the S locus glycoprotein (SLG), which has the same structure as the extracellular domain of SRK, is unclear, it may function as an accessory receptor, or alternatively, it may have a more general role in the pollen–stigma interactions. After activation, SRK phosphorylates ARC1, presumably initiating an intracellular signaling cascade within the papilla cell. Although a detailed analysis remains to be undertaken, evidence suggests that the signaling pathway may ultimately regulate the activity of aquaporins in the stigmatic papillae to limit the availability of water to the incompatible 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

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32 37 42 47 52

Phot

osyn

thes

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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

Quan

Highlight

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

Membranes

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

• 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


Photosynthesis

• Overall chemical reaction

+ ?


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



• Source of atmospheric oxygen

http://www.snowballearth.org/



• 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



• Source of energy for food chain

http://pack152.net/

Quan

Sticky Note

photoautotroph: photo --> enery source is light autotroph --> carbon source



• 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



• 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)



• 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

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


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


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

Quan

Sticky Note

guard cell: open the stomata


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/


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


Evans et al. (2009)

Step 1: cell wall

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

Flow

of C

O2

Red

uced

AQ

P1

Step 4: Chloroplast envelope

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!



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)

Quan

Highlight


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


Stage of Photosynthesis

• Two stages of photosynthesis

Light-dependent Reactions

Light-independent Reactions

Membranes

Anatomy, Structure and Function http://en.wikipedia.org/wiki/File:Common_lipids_lmaps.png

http://en.wikipedia.org/wiki/File:Common_lipids_lmaps.png

http://en.wikipedia.org/wiki/File:Common_lipids_lmaps.png

Lec 4 Membranes

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