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SEED DEVELOPMENT (MATURATION)
JULIO MARCOS-FILHO DEPT. OF CROP SCIENCE USP/ESALQ
INTRODUCTIONStart flower induction and differentiation
Seed development : a sequence of events controlled by the genotype Maturation: set of successive stages in preparation for successful seed germination Flowering and pollination are not uniform in the same plant or within a population 2
INTRODUCTIONInitial studies: aimed at determining phenological differences among species and the optimum harvest time
First proposed criteria to identify seed maturity: - Time from planting or seedling emergence to harvesting - Seed moisture content and morphological characteristics to identify seed maturity
3
SEED DEVELOPMENTDelouche (1971) : Seed maturation is a process that comprises a set of morphological, physical, physiological and biochemical events that occur from ovule fertilization to the moment in which seeds become physiologically independent of the parent plant4
RESERVE DEPOSITION (PHASE III)
DESICCATION (PHASE IV)
Embryo dry weight
CELL DIVISION AND ELONGATION (PHASES I and II)
HISTODIFFERENTIATION
Days after flowering Dure III (1975) 5
GENERAL PARAMETERS TO CHARACTERIZE SEED MATURATION
1960s and 1970s: individual seeds x plant population Seed sampling at pre-defined intervals and identification of parameters associated with maturation progress Definition of seed changes in seed technology research6
GENERAL PARAMETERS TO IDENTIFY SEED MATURATION
SEED MOISTURE CONTENT Ovule fertilization and evolution during maturation Dry fruits x Fleshy fruitsFinal dehydration7
Fresh weight
Moisture content
Dry weight TIME Variations in moisture content, fresh weight and dry weight during maturation of seed produced in dry (- - -) (or fleshy fruits ( ). 8 (Carvalho and Nakagawa, 2000)
GENERAL PARAMETERS TO IDENTIFY SEED MATURATION
SEED SIZE
R5
R6
Soybean pod and seed development (Ritchie et al., 1994) 9
GENERAL PARAMETERS TO IDENTIFY SEED MATURATION
SEED SIZE
R6
R7
R8
10
Species Cotton Soybean Sorghum Wheat
Period (days) 21-28 64 15-20 40
Reference Carvalho (1972) Jacinto and Carvalho (1974) Nagai (1973) Carvalho and Yanai (1976)
Days after flowering necessary for seeds of different species to attain maximum size during maturation (Carvalho and Nakagawa, 2000) (Carvalho 11
DRY WEIGHTnumber of cells Number of cells/seed x 10-6 dry weight6 30 4 20 2 10 (Dry weight (mg/seed) 40
Egli
2
5
8
11
Frut development period (Phase I)
12
SEED MOISTURE CONTENT + DRY WEIGHTMoisture content
GENERAL PARAMETERS TO IDENTIFY SEED MATURATION
Dry weight
Egli
13
Species Cotton Peanut Oat Field bean Maize Soybean Sorghum Wheat
Moisture content (%) 50-60 47-50 45 38-44 25-30 50 23-30 40
Reference Carvalho (1972) Carvalho et al. (1976) Frey et al. (1958) Neubern and Carvalho (1976) Hunter et al. (1991) Andrews (1966) Kersting et al. (1961) Carvalho and Yanai, 1976
Seed moisture content of different species at the time they reach reach maximum dry weight during development 14
GENERAL PARAMETERS TO IDENTIFY SEED MATURATION
GERMINATIONPrimary root protrusion x Normal seedlings Germination x Dormancy during maturation
VIGOR15
Species Rye Wheat Sorghum Clover Cotton Soybean
Germination (days after anthesis) 05 05 06 to 10 10 22 38
Initial germination (days) after ovule fertilization in some cultivated cultivated species (Delouche, 1971) (Delouche, 16
Days after sowing 78 84 90 96 102 108 111 117 123 126
Moisture content (%) 55.3 50.6 48.1 39.8 27.2 14.1 11.0 8.8 9.9 10.7
Seed dry weight (mg/seed) 20.40 25.34 28.80 34.10 36.44 34.10 37.24 37.54 37.90 37.84
Germination (%) 05 28 77 37 11 09 06 81 83 65
Vigor (mg dry weight / seedling) 5.0 4.07 7.47 7.69 4.86 4.88 5.53 9.57 10.72 9.34
Variation of seed moisture content, dry weight, germination and vigor during wheat maturation, cv. IAS -54. (Carvalho and Yanai, 1976) 17
DETERMINATION OF PHYSIOLOGICAL MATURITY
CONCEPTS a) Seed maturity is identified by the maximum dry matter accumulation b) Seed physiological maturity is reached when there are no significant increases in seed dry weight c) Seed physiological maturity occurs when seeds reach maximum dry weight, germination, and vigor 18
DETERMINATION OF PHYSIOLOGICAL MATURITY
PREVAILING IDEASeed physiological maturity = maximum dry weight Relative Maturity, Morphological Maturity, Mass Maturity, Harvest Maturity, Agronomic Maturity, Time of HarvestDetermination of physiological maturity in individuals or in plant communities19
MOISTURE CONTENT
SIZE
VIGOR
DRY WEIGHT GERMINATION
20
Days after sowing 64 70 76 79() 82 88 94 100 106
Moisture content (%) 72.9 60.5 56.8 43.9 38.2 21.8 41.0 30.0 18.1
Seed dry weight (mg/seed) 61.4 158.4 171.0 202.8 203.8 194.8 208.6 206.4 194.8
21
Mean values of moisture content and dry weight during maturation of bean seeds, cv Carioca (Neubern and Carvalho, 1976)
DETERMINATION OF PHYSIOLOGICAL MATURITY
Difficult to identify the exact point of seed physiological maturity (maximum dry weight) NEED TO INCREASE PRECISION: - Number of statistical replicates - Reduce harvesting intervals - Additional care in weighing Use of 14 C to monitor reserve accumulation22
DETERMINATION OF PHYSIOLOGICAL MATURITY
Visual indicators of seed physiological maturity MAIZE:Black Layer Milk Line
SOYBEAN: Pod and Seed Color23
PM100 80
Percentage
60 40 Green Yellow Yellow, typical of cultivar 20
49
63
77
90
Days after R3
Marcos-Filho (1979) 24
25
Black Layer
(Mississippi State University extension service, http://msucares.com/crops/corn/corn2.html)
Mature
Maturation of tomatoPhysiological potential OverripeContreras
26
Species Lettuce Onion Tobacco Maize Inbred Single hybrid Double hybrid Soybean Tomato Wheat
Mean period (days) 0 -4 0 0 -5 -10 -7 +10 -6
Average and range in days before or after physiological maturity and seed vigor maturity of different cultivated species (TeKrony and Egli, 1997) () (-): days before seed maximum dry weight ((+): days after seed maximum dry weight
27
Days after flowering 26 32 42 48
Germination() FD 00 00 65 54 SD 68 68 -93
Soluble Sugars() FD 1.1 1.5 2.2 1.6 SD 0.1 0.2 0.2 0.4
Proteins() FD 0.57 0.51 0.62 0.48 SD 0.09 0.18 0.25 0.19
Percentage germination, leakage of sugar and protein from soybean seeds, cv soybean Chippewea, submitted to drying at different maturation stages (Adams and Rinne, 1983) () FD seed threshing and fast drying immediately after harvest; SL slow seed drying still attached to pods. () Germination (%); Seed leachate (mg/seed)
28
Dry weight
Physiological Potential
Days after anthesisContreras
Maturation of tomato
29
SEED MATURITY X HARVEST TIME
- Determination of harvest time
- Delayed harvest: problems
30
Date (L1) 09/03/81 19/03/81 08/04/81 05/05/81 18/05/81
Yield (kg/ha) 5.255 4.493 4.398 3.904 3.888
Date (L2) 11/03/81 01/04/81 22/04/81 12/05/81 05/06/81
Yield (kg/ha) 5.104 4.797 4.695 4.440 4.236
Effect of harvest time on maize seed yield in two locations of Parana state, Brazil (Hadlich, 1983) 31
RH RH
RH
RH
RH
32
FIELD WEATHERING
33
YEAR 1973 1974 1975 1976 1977
PM 94 85 89 83 71
HT 88 83 85 28 62
14* 58 85 66 13 40
28* 55 41 57 07 05
Vigor (accelerated aging) of Kent soybean seeds as influenced by harvest time for five experimental years (TeKrony et al., 1980).
PM = physiological maturity; HT = adequate harvest time; 14 and 28 = days after HT
34
SEED MATURITY X HARVEST TIME
- Harvesting at physiological maturity? - Variations in seed moisture content and in plant characteristics - Visual parameters: black layer, milk line, seed and/or fruit color, glumes and pedicel35
SEED MATURITY X HARVEST TIME
- Uniformity of maturation
Soybean
Tomato
Cotton
36
I
II
III
Carrot
37
Umbel Order Primary Secondary Tertiary
Umbel / Plant 1 11 24
Proportion Germination First Count (%) (%) (%)
1000 seeds (g)
11 58 31
75 65 54
54 43 37
2.28 2.15 1.99
Number of umbels per plant, contribution to plant seed production (%), germination (%), vigor (germination first count - %) and weight of 1000 seeds associated with umbel order in carrot (Nascimento, 1991) 38
RESERVE ACCUMULATION DURING SEED DEVELOPMENT
- Sequence of genetically programmed events
- Monocots
endosperm; Dicots
cotyledons
- Final yield: seed number + seed growth rate + duration of seed fill39
RESERVE ACCUMULATION DURING SEED DEVELOPMENT 1. NUTRIENT TRANSLOCATION FROM THE PARENT PLANT
Photoassimilates (sugars, amino acids and other solutes) are transported via phloem Plant reserve accumulation in endospermic seeds Nutrient translocation to seeds Short distance transport40
NUTRIENT TRANSLOCATION short distance
starchy endosperm
transfer cells chalazal region
embryo basal endosperm pedicel phloem
41
RESERVE ACCUMULATION DURING SEED DEVELOPMENT 1. NUTRIENT TRANSLOCATION FROM THE PARENT PLANT
Plant reserve accumulation in non-endospermic seeds
42
NUTRIENT TRANSLOCATION short distance
f eeh
f
ct
43
RESERVE ACCUMULATION DURING SEED DEVELOPMENT 2. NUTRIENT ASSIMILATION
Mature seeds two or three main types of reserves Synthesis is parallel during seed development Synthesis occurs in different cellular compartments: starch, in amyloplasts lipids, in spherosomes proteins, in cytosol and endoplasmic reticulum44
2. NUTRIENT ASSIMILATION
Carbohydrates Lipids Proteins Nucleic acids
45
MAIZEDry Weight 300 mg 200 DNA 0,06 0,04 mg mg
100
0,02
30 Proteins mg 20 RNA
0,5 0,3
10
0,1
15
30
45 15 Days after fertilizationendosperm
30
45
46embryo
whole seed
2. NUTRIENT ASSIMILATION
LEGUMES
Accumulation of carbohydrates precedes those of lipids and proteins
47
50 40 30 20
Proteins
Percentage
Lipids
Carbohydrates 10
30
50
70
Days after flowering
Changes in carbohydrate, lipid and protein contents during soybean seed development (Adapted from Konno, 1979)
48
cell division140
cell elongation1400 7
100
RNA proteins
1000
5
60
600
3
20
200
1
10
14 18 Days after flowering
22
26
49
proteins (mg/cotyledon)
DNA (g/cotyledon)
DNA RNA (g/cotyledon)
Stage R4 R5 R6 R7 R8
Dry weight
(mg/seed) 0.2 5.9 123.6 194.2 188.3
M.C. (%) 78.4 83.1 62.4 51.9 9.7
Proteins Oil Sugars (mg/seed) (mg/seed) (mg/seed) ---------2.5 42.0 71.9 73.4 0.1 26.7 31.7 36.2 1.3 19.3 30.8 32.4
Variation in soybean composition during maturation (Dornbos and McDonald, 1986)50
HORMONES
Cytokinins Gibberellins Auxins Abscisic acid51
ENVIRONMENTAL FACTORS AFFECTING SEED DEVELOPMENT
- Soil Fertility Adequate supply - Water
seed size and weight
Effects of water deficits Water excess Time of occurrence Association with temperature stress
52
Association of water deficit and thermal stress during soybean seed filling (Frana Neto and Krzyzanowski) (Fran 53
alternate dry and humid periods
water deficit water deficit
APROSMAT, 2006
54
ENVIRONMENTAL FACTORS AFFECTING SEED DEVELOPMENT
- Temperature Critical value: 35oC during seed filling Forced maturation and greenish seeds
55
56
Germination (%)
Color
Tetrazolium 1-3 (%)
Emergence (%)
InitialYellow Green
3months
Initial 75 52
3months
Initial 87 58
3months
88 60
87 19
73 20
88 38
Soybean: presence of green seeds and effects on germination and vigor(Scheren and Tolentino Jr, 2005) 57
ENVIRONMENTAL FACTORS AFFECTING SEED DEVELOPMENT
- Light Photosynthesis x plant and seed performance Retention of flowers and fruits
- Seed position on the plant
58
ENVIRONMENTAL FACTORS AFFECTING SEED DEVELOPMENT
Seed 4-stage developmental pattern: cell division, cell elongation, reserve accumulation, desiccation Seeds do not germinate while attached to the parent plant During most of seed development: Formation and activity of enzymes involved in synthesis processes, managed by m-RNA59
METABOLISM REVERSION FROM DEVELOPMENT TO GERMINATION
Metabolic reversion from synthesis to hydrolysis Synthesis and activity of ABA High concentration during embryogenesis Synthesis and activity of ABA Decrease during late maturation desiccation Management by m-RNA60
HORMONE INFLUENCE
cyt
gib
aux
ABA
Seed dry weight
Fertilization
Maturity
61
Desiccation is the trigger to switch to metabolism reversion
synthesis
mobilization
Does drying play a role in this switch?Henk Hilhorst
62
Desiccation during seed maturation: developmental pattern, driving seed embryo to a quiescent stage in preparation for germination Desiccation Tolerance: The ability to recover biological functions after drying to equilibrium with moderately dry air and then resume normal function when rehydrated This ability depends on the ability to maintain membrane structure and prevent protein denaturation63
DESICCATION TOLERANCE DURING SEED MATURATION
Desiccation Tolerance: Intolerant Phase: Cell division and elongation + part of reserve accumulation period Tolerant Phase: Final phase of reserve accumulation Premature and rapid desiccation: Damage to enzyme and protein synthesis Loss of cell turgidity, damage to cell membranes, enzymes, proteins and nucleic acid structure64
DESICCATION TOLERANCE DURING SEED MATURATION
DESICCATION TOLERANCE DURING SEED MATURATION PROTECTIVE SUBSTANCES OR MECHANISMS
- LEA (late embryogenesis abundant) Proteins - Antioxidant systems - Soluble sugars: raffinose, stachyose, sucrose - Heat shock proteins - Slow drying65