Stach biosynthesis

1. SYNTHESIS AND ACCUMULATION OF
STARCH AND MOBILIZATION OF STARCH
DURING GERMINATION
BASIC BIOCHEMISTRY
BCM.501(2+1)
PRESENTED BY :
kiran dasanal
PALB7319
Jr. MSc(agri)
seed science and technology
22/05/2018
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2. CONTENTS
 Importance of starch
 Composition of starch
 Synthesis of starch
 ADPG-PP enzyme
 Enzymes limiting starch synthesis
 Mobilization of starch in cereals
 Mobilization of starch in pulses
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3. IMPORTANCE OF STARCH
 Most significant carbon reserve in plants (i.e. amount made
& distribution)
 Major component of crop plant yield in the world Major
source of calories in the human diet Important raw material
for industrial processes (e.g. potato & maize).
 A major component of food, feed and cloth.
 Starting material for ethanol production.
 Broad applications in the paper and textile industries.
 Owing to t heir biodegradable and renewable nature, they
are increasingly being considered as an environmentally-
friendly alternative to the use of synthetic additives.
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4. FACTS ABOUT STARCH
 Starch, a polysaccharide , is synthesized in the chloroplast.
 Starch formation occurs in plastids.
 Starch granules are classified as transitory or reserve.
Transitory starch granules accumulate for only a short
period of time before they are degraded, e.g.
a)Starch forms in leaf chloroplasts during the day.
b)hydrolyzed and transported to other plant parts
at night as simple sugar.
 Reserve starch, an energy storage for germination, a major
component of food and feed, and an industrial starting
material, is formed in amyloplasts.
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7. CONT…..
 Starch id widely found in Two forms:
 α - Amylose
 α - Amylopectin.
 α - amylose ; is a long chain polymer, where the
Glucose residues are linked by α ( 1 4) Glycosidic
bonds. It is a straight chain compound.
 It does not dissolve in water and with Iodine it gives
Blue color.
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8. CONT….
 α - amlopectin:
 It is a ploymer of having branched chain. The branching
in starch occurs for every 22 - 25 Glucose residues.
 It is branch chain having α ( 1 4), α ( 1 6)
glycosidic bonds.
 Amylopectin gives Reddish Violet color with Iodine.
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10. About ADPG-PP enzyme
 It is a heterotetramer (α2β2) has two large
units(regulatory properties) and two small units(catalytic
properties).
 Activity of this enzyme linked to starch accumulation.
 It is a rate of limiting enzyme
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11. Key enzymes limiting the starch synthesis
 Brittle-2:mutant of ADPG-PP,it removes the small sub
unit ie catalytic activity is last.
 Shrunken mutant(Sh-2):mutant for regulatory property
ie large sub unit of ADPG-PP.
 Sugery mutant:sucrose synthase enzyme is knocked
off.sucrose get accumulated in the cytosol of cell.
 Wrinkled mutant:only accumulation of amylose not
amylopectin.
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12. Days after fertilization
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13. UTILIZATION OF SEED RESERVES
DURING SEED GERMINATION
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14. MOBILIZATION OF STARCH DURING
GERMINATION
 In endosperm of cereals, starch degradation is takes
place in a non living tissue—effectively in an acidic,
apoplastic environment in which no intracellular or
intercellular compartmentation exists.
 Amyloplast envelope and the plasma membrane
disintegrate.
 Degradation of starch granule catalyzed by α-amylase
enzyme synthesized in scutellum.
 Later α-amylase enzyme synthesized in aleuron layer.
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15. CONT….
 Maltose is the major product of hydrolysis and further
broken into glucose by α-glucosidase(maltase) enzyme
present in the embryo ad aleuron layer.
 Finaly scutellum is a modified single cotyledon located
between the endosperm and the embryo.
 The epithelial cells of scutellum facilitate exchange
between the embryo and the endosperm.
 Glucose is absorbed from the endosperm and converted
to sucrose in scutellum and transported to embryo.
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16. BREAKDOWN OF STARCH IN CEREALS
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17. BREAKDOWN OF STARCH IN PULSES
DURING GERMINATION
 In legumes,the hydrolysis of cotyledonary reserves
commences after emergence and elongation of the
radicle.
 The plastid envelope is believed to disintegrate prior to
germination so that degradation occurs within the
cytosol.
 The initial slow phase is associated with activity of
starch phosphorylase.
 The more rapid degradation phase coincides with α and
β amylase activity.
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18. Cont….
 Later attacks the starch granules and cause to change the
starch strcture.
 Then the glucan water dikinase enzyme react with
glucan in presence of ATP and water it adds the β-
phosphate group of ATP to either the 3-or the6-carbon of
a glucosyl residue of amylopectin.
 Glucan + ATP+ water GWD
Glucan-p +AMP+ Inorganic
phosphate
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19. BREAKDOWN OF STARCH IN PULSES
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20. CONT…..
o The amyloplast mebrane disintegrates so that starch
degradation is catalysed by cytosolic enzymes.
o sucrose synthesized from starch is exported from the
starch-storing cells to the growing root and shoot of the
seedling.
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21. REFERENCES
 Seed science and technology by N C SINGHAL.
 Class notes of Dr uma shanker sir.
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22. THANK YOU
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