Golgi Apparatus
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Golgi bodies or “dictyosomes”
Stacks of cisternae
Secretory function
Cell wall formation
Golgi Apparatus: part of endomembrane system
Cell Wall Deposition: movement of cellulose synthase rosettes is guided by
microtubules in the cytoplasm. Problem or error here?
UDP-glucose (uridine diphosphate-glucose; cellulose precursor)
Cellulose microfibrils can’t “jump”; new microfibrils are always deposited
Below previously deposited microfibrils or cell wall layers.
Increased Golgi Activity during division
Progressive Stages of Cell Plate Formation
Cell Wall : 3 Layers
• Middle lamella:
– first layer formed during cell division
– outermost wall of cell, shared by adjacent cells
– Composed of pectins and proteins
• Primary (1°) wall:
– formed after mid. lam.
– cellulose micrifibrils in a gel-like matrix of pectins,
hemicellulose, proteins
• Secondary (2°) wall:
– formed once cell enlargement is complete.
– Extremely rigid and strong
– Cellulose, hemicellulose, lignin
Primary Cell Wall
• All plant cells (?) have a primary cell wall.
• Cellulose, pectin, hemicellulose, proteins
• All components are hydrophilic to a degree:
form a permeable hydrated matrix
Plasmodesmata
More Cell Wall & Plasmodesmata
Cell Expansion?
• Wall acidification: H+ pumps in cell membrane
move H+ into cell wall; disrupts crosslinkages
between cellulose, hemicellulose, pectins.
• Expansins : enzymes that can cause cellulose
microfibrils to slip.
• Hydrolytic enzymes: cellulase, pectinase,
degrade cell wall polymers
Secondary Wall
Photosynthesis
Chlorophylls
Chromophore
- Light-absorbing portion
- Conjugated ring system
- Absorption spectrum
modified by substitutions.
- Methyl group (chl a) 
Carboxyl (chl b)
- Absorption spectrum also
altered by nearby
molecules/interactions
“Tail”
- Unsubstituted chain of
C and H
- Hydrophobic (lipid-like)
- Anchors chlorophyll in
thylakoid membrane
Chlorophyll a
Chlorophyll b
Chlorophll absorption spectra
• Chlorophylls absorb blue
and red wavelengths
primarily.
• Chl a maxima:
• Chl b maxima:
What we see.
Chlorophyll Masking by Anthocyanins
• Malvidins – anthocyanins that absorb green/yellow wavelengths (+ UV)
• Impart blue/red/purple coloration (red wine, cherries, geraniums)
Chlorophyll masking by anthocyanin: a
defense for new growth?
Quercus marilandica (“blackjack oak”) Bastrop, TX.
- Predators may seek young, bright green leaves (anthocyanins camouflage the leaf).
- Other defenses of these young leaves? Felty appearance?
- In time, 2° defenses (tannin concentrations, etc.) may develop.
Degreening and Ripening
Absorption spectrum of Chlorophyll and
the Action Spectrum of Photosynthesis
Elgelmann’s Experiment (1882)
Overview of Photosynthesis
Resonance Energy Transfer in
Antenna Complex Pigments
Non-cyclic electron flow &
phosphorylation
Transfer of e- and H+