Cell wall in plants

Cell wall in plants- introduction, cell wall layers, functions, sugars the building blocks of cell wall, macromolecules of cell wall, cell wall architecture, biosynthesis and assembly

1. JAI NARAIN VYAS UNIVERSITY , JODHPUR Department of botany Paper- 101 Seminar topic : - Cell wall Submitted to : Dr . VINOD KATARIA Submitted by : Anmol Mertiya M.sc Previous 1 st sem

2. CONTENS 1. Introduction 2. Cell Wall Layers 3. Functions Of The Plant Cell Wall 4. Sugars :- Building Blocks Of The Cell Wall 5. Macromolecules Of The Cell Wall 6. Cell wall architecture 7. Cell wall biosynthesis and assembly 8. References

3. INTRODUTCTION :- Discovery of cell :- Cell wall was first observed and name by Robert Hooke in 1665. In 1804, Karl Rudolphi and J.H.F.Link proved that cells had indepent cell wall . The outermost structure of most plant cells is a dyanamic and rigid layer called cell wall ( buchanan 2000)

4. Cell Wall Layers :- There are three major regions of the wall. 1. middle lamella . 2 . Primary cell wall 3. Secondary cell wall a | Cell wall containing cellulose microfibrils, hemicellulose, pectin, lignin and soluble proteins. b | Cellulose synthase enzymes are in rosette complexes, which float in the plasma membrane. c | Lignification occurs in the S1, S2 and S3 layers of the cell wall.

5. Middle Lamella : This Outer Cell Wall Layer Contains Polysaccharides Called Pectins . Pectins Aid In Cell Adhesion By Helping The Cell Walls Of Adjacent Cells To Bind To One Another . Primary Cell Wall : This Layer Is Formed Between The Middle Lamella And Plasma Membrane. It Is Primarily Composed Of Cellulose Microfibrils (15-30%) , Petic Polysaccharides (30%) , Cross Linking Glycans (Hemicellulose (25%) And Protein (20%) . The Primary Cell Wall Provides The Strength And Flexibility Needed To Allow For Cell Growth .

6. This layer is formed between the primary cell wall and in some plant cells. This rigid layer strengthens and supports the cell. In addition to cellulose and hemicellulose, some secondary cell walls contain lignin. Lignin strengthens the cell wall and aids in water conductivity in plant vascular tissue cells. Secondary wall :

7. Middle lamella, Primary cell wall and Secondary cell wall :- While all plant cells have a middle lamella and primary cell wall, not all have a secondary cell wall .

8. Functions of the plant cell wall : maintaining/determining cell shape . support and mechanical strength . prevents the cell membrane from bursting in a hypotonic medium.  controls the rate and direction of cell growth and regulates cell volume ultimately responsible for the plant architectural design and controlling plant morphogenesis . metabolic role. physical barrier to : (a) pathogens (b) water in suberized cells.  However, remember that the wall is very porous and allows the free passage of small molecules, including proteins up to 60,000. economic products - cell walls are important for products such as paper, wood, fiber, energy, shelter, and even roughage in our diet.

9. Sugars : Building Blocks Of The Cell Wall :- Polysaccharides are long chains of sugar molecules covalently linked at various positions, some being decorated with side chain of various lengths. Sugars represent a vast spectrum of polyhydroxyl “ aldehydes ” ( aldoses ) and “ ketones ” ( ketoses ) that can be grouped according to their chemical formula, configuration , and stereochemical conformation.

10. Many sugars have the empirical formula ( CH2O )n, from which the term carbohydrate is derived. Haworth project 1. Pyranose 2. Furanose (5 membered ring ) ( 6 membered ring ) Chair Pu c kered

11. Sugars: building blocks of the cell wall The monosaccharides in cell wall polymers are derived from glucose .

12. Macromolecules of the cell wall 1. Cellulose 2. Callose 3. Cross-linking glycans 4. Pectin 5. Protein 6. Aromatic substance

13. Cellulose is the principal scaffolding component of all plant cell walls. Cellulose is the most adundant plant polysaccharide for 15-30 % of the dry mass of all primary cell and a much larger percentace of secondary wall M ade of (1→4)β- D-glucan chains hydrogen bonded to one another along their length Groups of 30 to 40 of these chains laterally hydrogen bond to form crystalline or para-crystalline microfibrils 1. Cellulose

14. 2. Callose Callose differs from cellulose in consisting of (1→3)β-D-glucan chains , which can form helical duplexes and triplexes Callose is made by a few cell types at specific stages of wall development, such as in growing pollen tubes and in the cell plates of dividing cells Callose is also made in response to wounding . Callose synthesis may also occue at the wall in response to abiotic or biotic stress.

15. 3 . Cross-linking glycans The most common hemicelluloses in cell walls are xyloglucans ( XyGs ) and Glucuronoarabinoxylans ( GAXs ). The XyG having β(1,4)-linked glucose residues that have α(1,6)-linked xylosyl side chains. The GAXs having β(1,4)-linked xylose residues. For ex . glucuronic acid to produce glucuroxylan . Both XyGs & GAXs may also be modified by acetylation, which affects their capacity to cross-link to other cell wall components. XyG is main hemicellulose in dicots primary walls & functions to cross-link cellulose microfibrils . Although GAXs are major hemicelluloses in secondary cell walls, they are also prominent in primary walls of monocots and some algae.

16. Structure of cross linking glycans

17. 4. Pectins P ectin s a mixture of heterogeneous, branched, and highly hydrated polysaccharides rich in D- galacturonic acid —have been defined classically as material extracted from the cell wall by Ca 2+ -chelators such as ammonium oxalate, EDTA, EGTA, or cyclohexane diamine tetraacetate. Pectins perform many functions : determining wall porosity providing charged surfaces that modulate wall pH and ion balance. regulating cell–cell adhesion at the middle lamella. serving as recognition molecules that alert plant cells to the presence of symbiotic organisms, pathogens, and insects.

18. Two types of pectine 1. HGA 2. RG Ⅰ ( Homogolacturonan) (Rhamnogalacturonan- Ⅰ) Homopolymers of (1 →4) α- D Gal A 2 parts 1.xylogalacturonamn 2. RG Ⅱ (Rhamnogalacturonan - Ⅱ) Rod- like heteropolymer of peating (1 → 2) α -1 Rha ( 1 → 4) α -D Gal A disaccaride unite

19. Structure of pectins

20. 5. Structural proteins Structural proteins of the cell wall are encoded by large multigene families. Although the structural framework of the cell wall is largely carbohydrate , structural proteins may also form networks in the wall. There are four major classes are structural proteins : hydroxy proline - rich glycoproteins ( HRGPs) proline – rich proteins ( PRPs ) glycine – rich proteins ( GRPs ) Arabinogalactan proteins ( AGPs )

21. Structure of structural proteins

22. 6 .Aromatic substances : Aromatic substances are present in the nonlignified walls of commelinoid species. The primary walls of the commelinoid orders of monocots and the Chenopodiaceae contain significant amounts of aromatic substances in their nonlignified cell walls-a feature that makes them fluorescent under ultraviolet (UV) light. Hydroxycinnamic acid are also reduced in the plant to hydroxycinnamoyl alcohols, which form the common precursors for lignin and lignan structures.

23. Cell wall architecture The primary wall consists of three structural networks: Cellulose and cross-linking glycans Matrix pectic polysaccharides Structural proteins or a phenylpropanoid network

24. Walls of angiosperms are arranged in two distinct types of architecture 1. Type I walls - most dicots and the noncommelinoid monocots contain about equal amounts of XyGs (xyloglucans) and cellulose In Type I walls the cellulose- XyG framework is embedded in a pectin matrix that controls, among other physiological properties, wall porosity. HGA is thought to be secreted as highly methyl-esterified polymers, and the enzyme pectin methylesterase (PME), located in the cell wall, cleaves some of the methyl groups to initiate binding of the carboxylate ions to Ca 2+ .

25. 2 . Type II walls - commelinoid monocots contain cellulose microfibrils similar to those of the Type I wall; instead of XyG, however, the principal polymers that interlock the microfibrils are GAXs (glucuronoarbinoxylans) . In general, Type II walls are pectin-poor , but an additional contribution to the charge density of the wall is provided by the α-L-GlcA units on GAX. These walls have very little structural protein compared with dicots and other monocots but they can accumulate extensive interconnecting networks of phenylpropanoids, particularly as the cells stop expanding.

26. Cell wall biosynthesis and assembly : Origin of cell wall takes place from cell plate during cytokinesis. Many cell wall vesicles provided by GB and ER combine to form a cell plate. After some physical and chemical changes, the cell plate ( rich in pectin ) grows on both sides to form a middle lamella, which glues neighbouring plant cells. After which primary wall and secondary walls are laid down on the middle lamella to from cell wall.

27. A fter a wall forms, it can grow and mature through a process:- 1 . Synthesis 2. Secretion 3. Assembly 4. Expansion ( in growing cells ) 5. Cross-linking and secondary wall fomation

28. Cell walls for food, feed, fuel, and fibers Wood Paper Textiles Fruits and vegetables for humans and animals Jams, jellies, thickening agents, emulsifiers Dietary fiber Biomass Biofuel: cellulosic ethanol

29. REFERENCES Alberts , B., Bray, D., Lewis, J., Raff, m., Roberts, K. And Watson, J. D. 1999. Molecular Biology Of Cell . Garland Publishing , Inc. , New York. Buchanan, B. B. , Gruissem , W. And Jones , R. L. 2000. Biochemistry And Molecular Biology Of Plants. American Society Of Plant Physiologists, Maryland, USA https://jcs.biologist.org