Seed germination and fruit ripening involve important biochemical reactions. During seed germination, respiration and the synthesis of proteins and nucleic acids provide energy and materials for growth. Stored reserves are mobilized through hydrolytic and phosphorolytic catabolism of starches, proteins, and lipids. In fruit ripening, hormonal changes like increased ethylene production cause chlorophyll degradation, color changes from carotenoids and anthocyanins, softening from cell wall degradation, and increased volatile and sugar production, resulting in a ripe, flavorful and aromatic fruit.

1. BIOCHEMISTRY OF
SEED
GERMINATION
AND FRUIT
RIPENING
JANANI PALPANDI
II BT
DEPT., OF BIOTECHNOLOGY,
MEPCO SCHLENK ENGG., COLLEGE.

2. BICHEMISTRY OF
SEED GERMINATION

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4. BIOCHEMICAL REACTIONS UNDERTHISTOPIC
• Respiration
• Protein and Nucleic Acid Synthesis
• Mobilization of stored reserves
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5. RESPIRATION
• In imbibed seeds the three metabolic pathways take place:
• Glycolysis
• Pentose Phosphate Pathway
• Citric Acid Cycle
• Through Glycolysis And Pentose Phosphate pathway – ATP, NADPH, FAD
produced.
• Through HMP shunt – NADP
• NADPH , NADP – Readily available reducing agents – utilized in bio-reductive
reactions
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6. RESPIRATION
• Dry seeds - 10-15 per cent water.
• Dry seeds - low level of respiration.
• Notable metabolic event during imbibition occurring in less than 15 min is the
reformation of keto acids from amino acids by deamination and
transamination.
• Divided into four phases.
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7. RESPIRATION
PHASE I
• Characterized by a sharp rise in
respiration for about 10 hours.
• Due to the activation and hydration
of mitochondrial enzymes.
• Enzymes - belonging to the cycle
and electron transport chain.
• There is rapid oxygen uptake into
seeds with intact testas during
phase I .
• Known as Early imbibition
PHASE II
• Involves a lag in respiration between
10 and 25 hours - after the start of
imbibition.
• Hydration of the cotyledons-
completed and all pre-existing
enzymes- activated.
• Testa impedes oxygen uptake in
phase II. (slows down).
• Between phase II and phase III, the
radicle penetrates the testa.
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8. RESPIRATION
PHASE III
• A second respiratory surge.
• Due to increased oxygen supply
through pierced testa.
• Another reason - newly synthesized
mitochondria and respiratory
enzymes in the dividing cells of the
growing axis.
PHASE IV
• Marked fall in respiration.
• disintegration of the cotyledons .
• exhaustion of the stored food.
• Early stages of germination,
respiration is cyanide-resistant and
the alternative oxidase instead of
cytochrome oxidase plays a role in
germination.
• . At later stages of germination,
however, respiration becomes
sensitive to cyanide.
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9. ROLE OF CYANIDE IN GERMINATION
• Cyanide is a germination regulatory agent.
• In some plants like Amaranthus at lower concentration it promotes seed
germination.
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10. PROTEIN AND NUCLEIC ACID SYNTHESIS
• Pre-requisite for radicle emergence .
• Protein synthesis does not occur in the dry seeds.
• Starts when these are hydrated and cytoplasmic ribosomes (eukaryotic SOS)
get associated with messenger RNA (mRNA).
• Radicle is the embryonic part from which root system develops.
• It is the first developed system.
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11. PROTEIN AND NUCLEIC ACID SYNTHESIS
• Initiation of protein synthesis - attachment of the
• small (40S) ribosomal subunit.
• tRNA molecule .
• Attachment to the initiation site on the mRNA.
• After formation of the initiation complex - the large (60S) ribosomal subunit
becomes attached .
• Protein synthesis begins.
• Formation of the initiation complex requires CTP and perhaps ATP.
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12. PROTEIN AND NUCLEIC ACID SYNTHESIS
• Other soluble protein factors - required for the transfer of aminoacyl-tRNAs to
their appropriate codons on the ribosome-mRNA complex.
• To move the message through the ribosome.
• These are the elongation factors requiring CTP for activity.
• New mRNA synthesis - not essential for resumption of protein synthesis
during the first hour of imbibition.
• mRNA conserved in the dry embryo - utilized for early protein synthesis.
• Even if new mRNA is synthesized as an early event, it is not involved in early
protein synthesis.
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13. PROTEIN AND NUCLEIC ACID SYNTHESIS
• Ribosomal RNA (rRNA) synthesis commences as early as mRNA
• Increases during and after imbibition - after the 6th hour coinciding with the
time of radicle elongation and
• At 16-18h it reaches a rate about 12-fold greater than the earlier stage.
• Although transfer RNA (tRNA) synthesis begins within 20 minutes in imbibing
embryos - not certain whether - involved in early protein synthesis.
• Its new synthesis is necessary during later stages to sustain-growth.
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14. PROTEIN AND NUCLEIC ACID SYNTHESIS
• The radicle within the seed initially grows by cell elongation.
• Emergence through the seed coat may be associated with cell division.
• DNA synthesis which is closely linked to mitotic cell division is mainly
concerned with the post-germination period of seedling development.
• During 9th hour – Inhibition of protein synthesis inhibits DNA synthesis.
• After 9th hour – Inhibition of protein synthesis – no action – in DNA synthesis.
• DNA polymerase synthesized de novo during germination during the first 9 h.
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15. MOBILIZATION OF STORED RESERVES
• II types of catabolic reactions:
• Hydrolytic involving Amylases
• Phosphorolytic
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16. HYDROLYTIC CATABOLISM
• In dicot seeds:
• starch degradation yields more glucose.
• more maltose is produced.
• This is related partly to the relative activity of cc-amylase in the two classes of
seeds.
• Two classes of seed – angiosperms and gymnosperms.
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17. • Storage proteins of seeds are hydrolyzed into their constituent amino acids by
proteinases or proteases.
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18. PHOSPOROLYTIC CATABOLISM
• Sucrose is the major form in which the products of carbohydrate catabolism
are transported into the developing seedling.
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19. BIOCHEMISTRY OF
FRUIT RIPENING

20. TYPES OF RIPENING
• Climacteric fruits – Able to ripen even after they a picked from the plants.
• Non-Climacteric Fruits – Able to ripen only if they are in plants.
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21. FRUIT RIPENING – PHYSIOLOGICAL CHANGES
• Softening – Both the skin and pulp.
• Flavor and Aroma – Increases.
• Chlorophyll loss – Development of new pigments ie., Carotenoids.
• Carotenoid accumulation.
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22. BIOCHEMICAL REACTIONS UNDERTHISTOPIC
• Hormonal changes – Ethylene.
• Change in chlorophyll content.
• Synthesis of pigments like carotenoids, anthocyanins and Xanthophylls.
• Increased activity of enzymes.
• Volatile components get synthesized.
• Simple Sugars get synthesized (gluconeogenesis).
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23. ETHYLENE
• Fruit ripening agent.
• Ripens the fruit even within minutes.
• Ethylene biosynthesis in plants:
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24. ETHYLENE
• Hastens the climacteric effects in the fruits.
• Accompanied by increased oxygen uptake.
• This process is not reversed.
• In the case of no-climacteric fruits:
• Once when the ethylene synthesis terminated
• Oxygen uptake and respiratory activity comes to control.
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25. DEGRADATION OF CHLOROPHYLL
• Ethylene promotes chlorophyll degradation.
• Change occurs in 3 steps:
• Replacement of Mg+ ion by hydrogen atom.
• Hydrloysis of chlorophyll.
• Bleaching of chlorophyll.
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26. Replacement of Mg+ ion
• Mg+ ion is replaced by hydrogen atom.
• Under acidic conditions.
• Associated with formation of Pheophytin.
• Pheophytin formation leads to color change – bright green to dull olive green.
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27. Hydrolysis of chlorophyll
• Chlorophyll hydrolysed to chlorophyllide and phytol.
• Catalysed by chlorophyllase.
• Results in formation of Pheophorbide.
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28. Bleaching of chlorophyll
• Through the action of:
• Lipoxygenase
• Peroxidase
• Catalase
• Degradation of fatty acids hydro peroxidases.
• Redox reaction in the presence of oxygen.
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29. SYNTHESIS OF OTHER PIGMENTS -
CAROTENOIDS
• Color change from green to red or orange.
• Isoprenoid compounds.
• Composed of isoprene units joined from head to tail by conjugated double
bonds.
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30. ANTHOCYANINS
• Responsible for red, pink, purple and blue color.
• Water soluble pigments.
• Flavonoid pigments.
• Composed of phenyl proponoid nucleus.
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31. XANTHOPHYLLS
• Isoprenoid pigment.
• Isoprene subunits joined form head to tail by conjugated double bonds.
• Substituted by oxy, hydroxyl, epoxy compounds.
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32. INCRESED ENZYME ACTIVITY
• Softening due to enzyme activity.
• Softening due to degradation of pectins.
• Catalysed by pectinases.
• Types of pectinases:
• PMG - Polymethyl galacturonases.
• PG – polygalaturonases.
• PE – Pectin esterases.
• PL – Pectin lyases.
• Degradation of Cellulose by cellulose.
• Hydrolysis of galactans to galactoses by B-galactosidase.
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33. SYTHESIS OFVOLATILE COMPOUNDS
• Aroma is produced by volatiles synthesized during ripening.
• Includes aldehydes, esters, lactones, terpenes, and sulfur compounds.
• Volatiles originate from proteins, carbohydrates, lipids, and vitamins.
• Taste is provided by many nonvolatile components, including sugars and acids
present in fruits.
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34. SYNTHESIS OF ORGANIC ACIDS AND SIMPLE
SUGARS
• Typical taste of fruits is determined by the content of sugars and organic
acids.
• Also phenolic compounds and tannins may affect the taste.
• During ripening starch is converted into sucrose, glucose and fructose.
• Starch hydrolysis is a major change during ripening of climacteric fruits.
• The concentration of organic acids also reach to a maximum during growth
and development of fruit on tree.
• Citric and malic acids-intermediates of Krebs cycle.
• Other acids: ascorbic acid (reduced form), oxalic acid.
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