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.
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
Chlorophylls Chlorophyll a Chlorophyll b “Tail” -Unsubstituted chain of C and H -Hydrophobic (lipid-like) -Anchors chlorophyll in thylakoid membrane 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
Chlorophll absorption spectra Chlorophylls absorb blue and red wavelengths primarily. Chl a maxima: Chl b maxima:
Chlorophyll masking by anthocyanin: a defense for new growth? - 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. Anthocyanins also become important during leaf degreening and fruit ripening Quercus marilandica (“blackjack oak”) Bastrop, TX.