LIPIDS IN ORGANIC MATTER AND ITS DEGRADATION

Lipid content in organic matter is important to soil as it degrades readily despite of its functional group.  Plants lipids are a source of metabolic energy. It is also the structural component of the membranes.  The stored plant lipids are accumulated in seed.  Lipids protects plant from water loss and pathogen.

LIPIDS ARE AS FOLLOWS:

  • FATTY ACIDS:

Fatty acids are simple lipid. They are long hydrocarbon chain with a carboxylic acid group. Fatty acids can be saturated or unsaturated. Saturated fatty acid have no double bond i.e. they are saturated with hydrogen whereas, unsaturated fatty acid have at least one double bond within the fatty acid chain. Formation of double bond removes a hydrogen atom from carbon. Fatty acids are monounsaturated when there is a presence of one double bond and when more than one double bond is present it is termed as polyunsaturated fatty acid.

  • FATS AND OILS:

Fats and oils are formed when fatty acid is attached by ester linkages to glycerol.  When one fatty acid is attached to glycerol molecule through ester linkage it is termed as monoglyceride similarly when two fatty acid are attached it is diglyceride and if three fatty acid are attached to glycerol it is known as triglyceride.

  • Examples of fats: Palm and coconut are triglyceride. They are saturated fatty acid and are solid at room temperature. Lesser amount of saturated fatty acid such as lauric and myristic acid are also present. Whereas, phytanic acid derived from chlorophyll metabolism is a branched chain fatty acid that cannot undergo β-oxidation due to methyl group at 3rd position (Wanders et al., 2011).

 

  • Examples of Oils: Peanut (ground nut), soybean, olive, mustard and sunflower are unsaturated fatty acid and are in a liquid state. Presence of oleic (one double bond), linoleic acid (two double bond) and α – linolenic acid (three double bond) increase the fluidity of the membrane.

 

WAXES, CUTIN, SUBERIN:

  • Waxes and cutin are found in the cuticle which is above the epidermal cell. Plant waxes are long chain fatty acid attached to a long chain alcohol by ester linkage. Plant cuticular waxes serve as protective barrier against water loss (Jetter and Kunst 2008).
  • Cutin is part of the structural component of the cuticle. It is an amorphous substance composed of interesterified hydroxyl and epoxy-hydroxyl fatty acid with chain length of 16 or 18 carbon (Nawrath 2002).
  • Suberin is a complex polyester formed from poly-functional long chain fatty acid (suberin acid) and glycerol (Garca 2015). It is found in periderm, epidermis and hypodermis as well as in casparian strip of root endodermis. Suberin may be deposited in bundle sheath, the chalazea and abscission zone during seed development as well as in secretory organ and fiber (Kolattukudy 1981). It is also deposited in response to injury or pathogen attack. Cutin, waxes and suberins protect plants from dehydration and pathogen attack.

 

  • GLYCEROPHOSPHOLIPID OR PHOSPHOGLYCERIDE:

Glycerophospholipid make up the plasma membrane. It is synthesized from phosphatidic acid by esterification of phosphoric acid residue. Molecule like choline, serine and inositol become esterified by their hydroxyl groups to phosphatidic acid and forms phosphatidylcholine (lecithin), phosphatidyl inositol and phosphatidyl serine.

 

  • GLYCOSYLGLYCERIDES:

Glycosylglycerides is present in plant chloroplast membrane. The two galactose containing lipids – monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) represents 40% of the dry weight of photosynthetic membranes (Gurr et al., 2016). Galactose is the only sugar found in glycosylglyceride (especially in higher plants). In bacteria several combination are found in glycosyldiacylglycerol. The most common combination are two glucose, two galactose or two mannose residue. The sulpholipid occur in small amount in photosynthetic bacteria and some fungi and is characteristic of the photosynthetic membranes of chloroplast and cyanobacteria (Gurr et al., 2016).

  • STEROIDS:

Plant steroids are present in the plasma membrane. Steroids is composed of 17 carbon atom bonded in four fused ring . The three cyclo hexane ring  and one five member cyclopentane ring  forms varied kind of steroid with different biological activity. They function as hormones. Sitosterol, stigmasterol and campesterol are plant steroids, supplied by vegetable oil. Oils are rich source of steryl ester (Piironen et al., 2000). Brassinosteroid is the most bioactive form of growth promoting plant steroid (Bishop and Koncz  2002).  Ergosterol is present in yeast and fungi.

 

  • TERPENES:

Terpenes are lipid containing two or more isoprene unit. The aroma and flavor of many plants are because of terpenes. Example phytol a constituent of chlorophyll, β-carotene a photosynthetic pigment (precursor of Vitamin A).

Terpenes are composed of isoprene {isoprene (C5H8) is a gaseous hydrocarbon} unit having 5n carbon atom (where n is an integer)

TERPENE               Isoprene Unit       Carbon Atom

Monoterpenes              2.0                           C10

Sesquiterpenes             3.0                           C15

Diterpenes                     4.0                           C20

Sesterterpene               5.0                            C25

Triterpene                      6.0                           C30

 

  • TOCOPHEROL:

Tocopherol consists of an aromatic ring and a long isoprene chain. Plant tocopherol include Vitamin E (biological antioxidant) that protect unsaturated fatty acid from damage from free radical attack. Phytol obtained from degradation of chlorophyll is used in biosynthesis of tocopherol (Mach 2015).

Fatty acids are a source of metabolic energy. The degradation and synthesis depends on the availability of fatty acid. β-oxidation is degradation of fatty acid to yield Acetyl CoA (a building block of many essential natural substances) and metabolic energy. The peroxisomal and mitochondrial β-oxidation use fatty acid (Kretschmer et al., 2012).

Lipases are produced by plant, animals, bacteria, yeast and fungi (Nagarajan 2012). Lipids can be degrade by lipases.  Lipases hydrolyze triglycerol, releasing one fatty acid at a time and eventually produces glycerol. Seed lipases quickly hydrolyze a variety of fatty acid. Lipases or triacylglycerol acyl hydrolases (E.C.3.1.1.3) catalyze the hydrolysis of ester bond in fats and oils into glycerol and free fatty acid at the substrate-water interface (Treichel et al., 2010). Beside hydrolysis lipases can catalyze synthesis reaction such as esterification, amidation, alcoholysis, acidolysis and aminolysis (Casas-Godoy et al., 2012).

The lipid content in soil aid in formation of soil aggregates and the soil microorganisms can contribute in bioremediation of oil spills.

 

References:

Bishop G. J. and Koncz, C. 2002 Brassinosteroids and Plant Steroid Hormone Signaling. The Plant Cell 14 (Suppl): s97–s110

doi:  10.1105/tpc.001461

Casas-Godoy, L., Duquesne, S., Bordes, F., Sandoval, G and Marty, A. 2012 Lipases: an Overview.  Methods in Molecular Biology 861: 3–30

Graça, J. 2015 Suberin: the Biopolyester at the Frontier of Plants. Frontiers in Chemistry 3: 62

doi: 10.3389/fchem.2015.00062

Gurr, M. I., Harwood, J. L.,  Frayn, K. N.,  Murphy, D. J., and  Michell,  R. H. 2016 Important Biological Lipids and their Structure  in “Lipids: Biochemistry, Biotechnology and Health” John Wiley & Sons Ltd. UK Chapter 2 (2.3.2.3): 29

Jetter, R. and Kunst, L. 2008 Plant Surface Lipid Biosynthetic Pathways and their Utility for Metabolic Engineering of Waxes and Hydrocarbon Biofuels. The Plant Journ. 54 (4): 670 – 683

doi: 10.1111/j.1365-313X.2008.03467.x

Kretschmer, M., Wang, J. and Kronstad,   J. W. 2012 Peroxisomal and Mitochondrial β-Oxidation Pathways Influence the Virulence of the Pathogenic Fungus Cryptococcus neoformans Eukaryot Cell 11 (8): 1042–1054

doi:  10.1128/EC.00128-12

Kolattukudy P. E. 1981 Structure, biosynthesis, and biodegradation of cutin and suberin. Ann. Rev. Plant. Physiol. 321 (1): 539–567

Mach, J.  2015 Phytol from Degradation of Chlorophyll Feeds Biosynthesis of Tocopherols. Plant Cell 27 (10): 2676

doi:  10.1105/tpc.15.00860

Nagarajan, S. 2012 New Tools for Exploring Old Friends-Microbial Lipases. Applied Biochemistry and Biotechnology 168 (5): 1163–1196

Nawrath, C.   2002 The Biopolymers Cutin and Suberin.   The Arabidopsis Book 1: e0021

doi:  10.1199/tab.0021

Piironen, V., Lindsay, D. G., Miettinen, T. A., Toivo, J. and Lampi Anna-Maija 2000 Plant Sterols: Biosynthesis, Biological Function and their Importance to Human Nutrition.  Journal of the Science of Food and Agriculture 80: 939 – 966

doi: 10.1002/(SICI) 1097-0010(20000515)80:7<939::AID-JSFA644>3.0.CO;2-C

Treichel, H., de Oliveira, D.,  Mazutti, M. A., di Luccio, M. and Oliveira, J. V. 2010 A Review on Microbial Lipases Production.  Food and Bioprocess Technology 3 (2):  182–196

doi: 10.1007/s11947-009-0202-2

Wanders, R. J. A., Komen, J. and Ferdinandusse, S. 2011 Phytanic Acid Metabolism in Health and Disease.  Biochimica et Biophysica Acta (BBA) – Molecular and Cell Biology of Lipids

1811 (9):  498–507

doi.org/10.1016/j.bbalip.2011.06.006

 

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