Selaginella: features, morphology ,anatomy and reproduction.
Seed ageing
1. Speaker: Rajesh Kanwar
(H-13-33-D)
Department of Seed Science and Technology
College of Horticulture
Dr. Y.S. Parmar University of Horticulture and Forestry, Nauni 173230
Solan (H.P.)
2. All living organisms must eventually deteriorate and die.
Seeds being living entities also go through series of changes,
leading to reduction in seed quality, performance and stand
establishment before they finally loose germinability.
Soon after the physiological maturity, seeds enter the storage
phase and are exposed to ageing.
Seed deterioration involves almost every system with in the
seed, many enzymes and apparently all organelles are
affected.
3. Seed needs to be stored from the day of
harvest up to the time of next sowing.
Seed in storage are the main recurring assets
for growers.
Seeds are generally stored either for:
(a) Short term: 6-9 months, storage of seed from harvest to next
planting. The majority of seed we are dealing will fall in this
category (75 - 80%)
(b) Medium term: 16 - 36 months, storage of carryover seeds.
Seeds that may not be produced every year (20 -25%)
(c) Long terms: 5 -20 years, storage of germplasm and breeder
seed (5%)
6. Seed ageing adversely affect three important
physiological drivers:
Germination potential
Vigour and viability
Radha et al., 2013 reported protein deterioration in maize seeds
following ageing resulting in loss in vigour and viability.
Leading to
Poor emergence
Staggered and non uniform
field establishment “Skips”
Uneven maturity
7. Seed Ageing further weakens the defense
mechanism of the plant against various biotic
and non biotic stressors.
Diseased crops
8. “Deteriorative changes occurring within seed with
time that increase its vulnerability to external
challenges and decrease the ability to survive.”
deteriorative
changes
enhanced
increased
exposure of
seed to external
challenges
decreases
ability of the
seed to survive
9. Inexorable process- All living thing eventually
deteriorate and die;can be retarded
Irreversible process- Once seed deterioration has occurred,
this can not be reversed
Varies among seed population- It is now well established
that certain varieties exhibit less deterioration than others. Even
within a variety, the storage potential of individual lots varies,
and even within a seed lot individual seeds have differing storage
potential.
10. Does not occur uniformly in seed
In Dicots: Deterioration begins
in growing points (shoot
and root) of embryonic axis.
In Monocots: Deterioration begins in root tip. Causes radicle
extension to be reduced more than coleoptile extension.
19. Macromolecules oxidation
Oxidative degradation of lipids, proteins, enzymes and
nucleic acids.
What is a free radical ?
An atom or molecule that possesses an unpaired electron is a
free radical.
Formed by :-
ionizing radiation
spliting of oxygen by enzymes or transition metals
by normal metabolic processes
(McDonald, 1999; and Murthy et al., 2003)
O, O3, O2, O2
+, O2
- ,OH ˉ are free radicals
20.
21. The short lived radicals produced during autoxidation
can be damaging to proteins, enzymes and other
biological compounds in their proximity.
metal ions
1. Unsaturated Fats Free radicals
light and other irradiation
2. Free radicles + 02 Hydroperoxides
3. Hydroperoxides Carbonyls
4. Carbonyls + protein Inactivation of enzymes, membrane
injury
5. Carbonyls + nucleic acids Chromosomal mutation
The sequence of events during lipid autooxidation in seeds (From J.F. Harrington,
“Biochemical basis of seed longevity," Seed Science and Technology, 1973, 1:
458.)
22. (b) Degradation of functional Structures
Cellular membrane lose their selective permeability,
permitting the cytoplasmic metabolites to leach into the
intercellular spaces. Membrane degradation occurs
from both hydrolysis of phospholipids by
phospholipase and phospholipid autoxidation.
23. Mitochondrial degradation and functional changes
appear(becomes permanently swollen and lose their natural
swelling contracting ability, later become pigmented and
fragmented).
Two important aspects of
mitochondrial deterioration
are an increase in ATPase and
decline in oxidative
phosphorylation ability.
(Priestley, 1986; Walters, 1998 and Murthy et al., 2003)
24. (c) Inability of Ribosomes to Dissociate
Evidence indicate that dissociation of polyribosomes must
occur
before attachment
of preformed
mRNA can occur
leading to protein
synthesis in
germinating
seedlings.
In non viable seeds, the ribosomes fail to dissociate and protein
synthesis is retarded. Such decline is a measurable symptom of
ageing.
(Smith and Berjak, 1995 and Walters, 1998)
25. (d) Enzyme Degradation and Inactivation
Decreased activity of enzymes such as catalase,
dehydrogenase and glutamic acid decarboxylase.
(Bailly, 2004; Lehner et al., 2008
and Goel et al., 2002)
26. (e) Formation and Activation of Hydrolytic Enzymes
As seed moisture content approaches levels necessary for
germination, hydrolytic enzymes are activated. If the seed
moisture content remains high or reaches higher levels,
normal germination may occur, however, if moisture levels
for germination are not attained, the seed deteriorates
because of energy expenditure or accumulation of
breakdown products.
( Copeland and Mc Donald, 1985)
(f) Breakdown in Mechanisms for Triggering Germination
Harrington (1973) has made a strong case for the idea that
the breakdown of various triggering mechanisms also
causes seed deterioration.
27. (g) Genetic Degradation
Progressive fragmentation of
embryonic nuclear DNA occurs
during seed ageing. DNA damage
can be due to an uncontrolled
degradation following extensive
DNA oxidation or to DNA
laddering, as is commonly
observed in active and genetically
controlled programmed cell death.
(Shaban 2013)
(h) Starvation of Meristematic cells
Respiration may deplete the tissues involved in the transfer of
nutrition from reserve storage areas and thus prevent them from
reaching the embryo. It was speculated that perhaps the
meristematic cells exhausted their energy supply, with no way to
convert ADP to ATP.
28. (i) Accumulation of Toxic Compounds
Under low moisture storage, the reduced respiration
and enzyme activity may be responsible for
accumulation of toxic substances that reduce seed
viability. Presence of abscisic acid, a germination
inhibitor, in several seeds supports this theory as a
probable cause of ageing.
29. Relation of moisture content of seed and auto
oxidation and degradation
Below6%
Autoxidation is
primary cause
of seed
deterioration
Between 6-14 %
LP IS minimum
because
sufficient water
is available act
as a buffer
against
autoxidatively
generated free
radical attack
Above 14 %
LP stimulated
by the activity
of hydrolytic
oxidative
enzymes such
as
lipoxygenase,
30. Scheme to illlustrate a variety of causes that may be
involved in loss of viability in stored seeds
Osborne, 1980
31. Zacheo et al., (1998) reported that the content of lipid decreased
during accelerated ageing in almond seeds. The aged seeds
contained high levels of malondialdehyde, a product of the
peroxidation of unsaturated fats and increased Lipoxygenase
activity, which hydrolises unsaturated fatty acids.
Shaban (2013) working in soyabean and sunflower and Radha et
al., (2014) working in maize, inferred that autooxidation of lipids
and increase in the content of free fatty acids during storage
period are the main reasons for rapid deterioration of seed. Aged
seeds show decreased vigour and produce weak seedlings that are
unable to survive once reintroduced into a habitat. Ageing induce
damage to cellular membranes, decrease in mitochondrial
dehydrogenases activities, chromosomal aberration and DNA
degradation increases.
32. Tubić et al., (2005) determined the degree of
biochemical changes during accelerated and natural
aging on 5 cultivars of sunflower seed. Lipid
peroxidation and decrease in superoxide dismutase
and peroxidase activities (especially pronounced in
accelerated aging variant) were caused by both types
of aging.
34. Mustafa et al., 2010 investigated the changes in antioxidant
enzymes like CAT and SOD at different viability levels in
seeds of three onion cultivars ‘Akgün-12’, ‘Valencia’ and
‘TEG-502’. For this purpose, 95, 80, 60, 40 and 20%
germination levels were obtained through the use of controlled
deterioration treatments in seeds. The activities of CAT and
SOD decreased due to seed ageing in each cultivar.
36. Seed symptoms:
Morphological changes:
Darkening of the seed coat in deteriorating
clover, peanut and soybean seeds have
been reported.
Other morphological changes have been reported in
deteriorating lettuce seeds which
develop red necrotic lesions in
the cotyledons
(Cotyledonary necrosis).
37. Ultrastructure Changes
The ultrastructure changes using electron microscopy and two
general patterns of coalescence of lipid bodies and plasma
lemma withdrawal with deterioration have been observed.
Coalescence of lipid bodies in the embryo has been found in
broad group of species. Withdrawal of the plasma lemma also
has been detected in these species (wheat, peas and pine). It is
significant that both of these events influence cell membrane
integrity.
38.
39. Cell Membranes
Loss in integrity
The increased leakage was attributed for membrane
disruptions, associated with loss of membrane
phospholipids. This loss may be due to either
phospholipase enzyme activity or lipid auto oxidation.
40. Loss of Enzyme Activity
Enzymes that have been correlated with seed
deterioration are dehydrogenase, catalase, peroxidase,
amylase and cytochrome oxidase etc.
Reduced Respiration
As seeds deteriorate, respiration becomes
progressively weaker, and leads to loss of
germination.
41. Increase In Seed Leachate
The exudes are a reflection of the amount of
membrane degradation that has occurred. The
leachate concentration has been measured by
electrical conductivity.
Increase In Free Fatty Acid Content
Continuous accumulation of free fatty acid
culminates in a reduction of cellular PH and is
detrimental to normal cellular loss of activity.
42. Reduced vigour and viability
Loss of field emergence potential
Decreased resistance to environmental stresses
Morphologically abnormal seedlings may be
produced
Example: Aged onion seeds do not develop
the cotyledonary knee necessary for
emergence through the soil
Aged lettuce seeds showed lack of hypocotyl
elongaion and stunting of the radicle
43. Nik et al., (2011) incubated cotton seeds in sealed containers at two
different temperatures of 34°C (Exp. 1) and 40°C (Exp. 2) for 24,
48, 72 and 96 hours and indicated that seed deterioration results in
decreased germination percentage, rate of germination and
decresed percentage of normal seedlings due to significant
reduction in the fraction of seed reserves which are mobilized to
seedling tissues.
45. Radha et al., (2013) subjected maize seeds to
accelerated ageing treatment at two temperature
levels (40ºC & 42ºC) and three relative humidity
levels (90, 95 & 100 per cent) for 0, 3, 6, 9 and 12
days in a controlled ageing chamber and reported
decreased vigour and viability and impairment in the
quantity and quality total soluble protein content with
increased ageing.
47. Harvesting
(a) Physiological maturity and Harvest Maturity
e.g., Red fruit colour of Capsicum
Rao et al., 2008 studied the storage potential of seeds harvested
at 14, 21, 28, 35 and 42 DAP in pearl millet cv 5141A. A
comparison of P50 among seeds harvested at different duration
showed that seeds harvested at 42 DAP retained maximum
longevity stored at 40 0C with 13 % moisture content.
They concluded that maximum seed longevity (p50) was attained
one week after physiological maturity (defined as the end of the
grain filling period), which is therefore the optimum time of
harvest to obtain good quality seeds for conservation.
48. Processing
(a) Threshing (should be done when
moisture content of seed declines
to 13-18%, thereby imparting mechanical
strength.
(b) Processing unit should offer
minimum damage to the seeds
49. Storage:
◦ (a) Storage place
The climate of the place where the seed storage is
located affects the life of the seed. A much better and, more
expensive seed storage is needed in tropical region like TN,
Coimbatore then compared to temperate regions like HP, Jammu
& Kashmir.
(b) Drying seed to safe moisture content
In general, cereals are dried to 10-13% and vegetables
are dried to 6-8%.
(c) Adopt good packaging material
In India, certified seeds of cereals, pulses and oilseeds
are normally packed either in jute bags or cloth bags whereas paper
bags, cardboard boxes, aluminium foil pouches, polythene bags are
used for packaging flowers and vegetable seeds.
Agro climatic condition should be taken into account
50. ◦ (c) Pre storage treatments:
i. Halogenation
ii. Antioxidant treatment
iii. Seed sanitation
iv. Seed fumigation
55. Table-2. Effect of seed priming on seed vigour index in different vigour group of bitter gourd seeds. (Paper
Towel Method)
Seed Priming Seedling Vigour Index-I Seedling Vigour Index-II
V1 V2 Mean (P) V1 V2 Mean (P)
PEG ( -1
Mpa )
1494.26
1187.85
1341.06 11469.90 9155.15 10312.53
KNO3 @ 1% 1424.21 1112.48 1268.34 11023.67 8826.38 9925.03
KH2PO4 @ 1% 1412.77 1102.17 1257.47 10856.45 8705.88 9781.16
CuSo4 @ 100
ppm
1143.17
1061.91
1102.54 9349.69 8024.50 8687.10
Cocopeat 1662.88 1269.67 1466.27 12384.35 9564.69 10974.52
Perlite 1786.57 1322.92 1554.74 12609.17 9842.05 11225.61
Vermiculite 1586.94 1224.00 1405.47 11934.15 9268.15 10601.15
Soaking in water 1383.17 1084.52 1233.84 10586.95 8459.50 9523.23
Control 1051.42 707.77 879.59 9281.20 6498.95 7890.08
Mean (V) 1438.37 1119.25 11055.06 8705.03
Mehta and Kanwar, 2013
56. Seed Ageing is an inexorable and irreversible process.
Seed being a living entity will always remain vulnerable
to ageing.
Seed deterioration is not confined to any one cellular
function but is manifested in a variety of ways, anyone of
which might be sufficient to impede germination.
Moisture content of seed, storage oxygen, relative
humidity and temperature are the most important factors
in storage which greatly influence the longevity and
storability of seed.
57. Understanding factors influencing physiological, biochemical and
ultrastructural properties of seed during ageing provides direction
towards establishing an effective way to delay the deleterious effect
of seed ageing and thereby improve the storage potential of the seed
lot.
The most fundamental objective of seed storage is to preserve and
maintain physiological quality of seed through out the storage
period by minimizing seed deterioration.
Scientific and intelligent post harvest handling approach would not
only delay the ageing effect but would also reduce the deteriorative
impact of ageing on seed.
Seed longevity is a major challenge for the conservation of plant
biodiversity and for crop success. Seeds possess a wide range of
systems (protection, detoxification, repair) allowing them to survive
in the dry state and to preserve a high germination ability.
Therefore, the seed system provides an appropriate model to study
longevity and aging
