Seeds and Germination

Question 1

Double fertilization

Answer 1

Product of fertilization of egg in ovule; results from fusion of sperm nuclei w/egg cell and polar nuclei.

• one sperm nucleus fuses w/2 polar nuclei –> 3n endosperm
• one sperm nucleus fuses w/egg –> embryo (2n)

Question 2

Function of seed coat

Answer 2

protection

Question 3

function of embryo

Answer 3

seedling plant

Question 4

function of endosperm and/or cotyedon

Answer 4

stored food to support seedling growth

Question 5

function of enzymes and hormones

Answer 5

digest stored food to create energy and control cell division and development

Question 6

carbohydrates include

Answer 6

starches, pentosans, mucilages

Question 7

starches include

Answer 7

amylase and amylopectin

Question 8

amylose

Answer 8

long chain glucose polymers. 100% digestible by amylase, makes up starchy endosperm

Question 9

amylopectin

Answer 9

glucose polymers with side glucose chains, only 50% digestible by amylase, makes up waxy endosperm

Question 10

pentosans

Answer 10

strongly imbibe water, found in coats of certain seeds

Question 11

mucilages

Answer 11

polyuromides and galactomides, become sticky when wet

Question 12

Lipids include

Answer 12

oils, fats, waxes

Question 13

oils

Answer 13

Liquid at normal temps: principal energy storage in many species; frequently found in starchy seeds; seeds high in oil tend to be high in protein
Typically high in unsaturated fatty acids: degree of unsaturation relates to # of double bonds

Question 14

fats

Answer 14

Typically solid at normal temps.

Generally higher in saturation (fewer double bonds)

Question 15

waxes

Answer 15

Esters off fatty acids and a monohydric alcohol

In seed coats

Question 16

Proteins include

Answer 16

albumins, globulins, glutelins, prolamins

Question 17

Albumins

Answer 17

water soluble; includes enzymes; coagulate at high temp

Question 18

Globulins

Answer 18

Soluble in water and salt solutions; do not readily coagulate with heating; Legumes are high in globulins (gycinin in soybean)

Question 19

Glutelins

Answer 19

Insoluble in water but soluble in salt, acid, and alkali.

Bread wheats contain glutenin

Question 20

Prolamins

Answer 20

Soluble in alcohol
Good source of N to seedlings
Zein in corn, gliadin in wheat, and hordenin in barley

Question 21

Other seed compounds

Answer 21

phytin, alkaloids, phenolics

Question 22

Phytin

Answer 22

Primary source of P to germination seedling.

Released by enzyme phytase from aleurone layer

Question 23

Alkaloids

Answer 23

Cyclic Nitrogenous storage compounds.
Include caffeine, nicotine, morphine strychnine, etc.
Can serve as allelochemicals

Question 24

Phenolics

Answer 24

also called actones.
Include tannins, courmarin, caffeic acid, etc.
Can serve as dormancy mechanism by inhibiting

Question 25

Five requirements for germination

Answer 25

1. Germinable seed 2. Moisture 3. Adequate temp 4. Oxygen 5. Light

Question 26

Nine steps in germination process

Answer 26

1. Inhibition of water 2. Hydration of tissues 3. Absorption of O2 4. Enzyme activation 5. Digestion of stored food reserves 6. Transport of hydrolyzed reserves to embryo 7. Increase in respiration 8. Cell division and enlargement 9. Embryo emergence

Question 27

What hormones are involved in germination and what does each hormone do?

Answer 27

1. Gibberellins: activate hydrolytic digestive enzymes 2. Cytokinins: stimulate cell division in the embryo 3. Auxins: promote growth through enlargement of coleohiza, radicle and plumule; activate geotropism (grows to the earth; responds to gravity)

Question 28

What enzymes are involved in germination and what does each do?

Answer 28

1. Hydrolases- hydrolyze cell contents into constituent parts - Proteases - Lipases - Amylase 2. Nucleases- help dissolve cell membranes

Question 29

Dormancy

Answer 29

when viable seeds do not germinate even though conditions are favorable

Question 30

What are the four causes of dormancy?

Answer 30

1. immature embryo - found in orchidaceae, witchweed 2. impermeable seed coat - impermeable to water, e.g. clovers - impermeable to O2; e.g. wild oats 3. mechanical resistance - imbibe water, but resist embryo emergence, e.g. nuts 4. physiological or embryo dormancy - requires after ripening to overcome hormone imbalance

Question 31

What methods can be used to overcome dormancy

Answer 31

scarification, stratification, leaching

Question 32

Scarification

Answer 32

scratch the seed coat mechanically or chemically | - allow water and oxygen to enter

Question 33

stratification

Answer 33

place seeds in moist, cool or cold environment

Question 34

leaching

Answer 34

wash with fresh water for 12-48 hrs to remove inhibitors in seed coat

Question 35

What factors affect seed quality?

Answer 35

1. conditions during fill 2. seed storage conditions - moisture content - storage environment > temp 0-32 degrees F idea; 32-50 degrees F adequate > relative humidity of 50-60% > reduced O2 concentration 3. length of storage

Question 36

Seed purity

Answer 36

percentage of pure seed

Question 37

possible contaminants for seed purity

Answer 37

``` seed of other crops. Weed seed - Primary noxious weeds (prohibited) - Secondary noxious (restricted) Insect matter ```

Question 38

Standard seed germination test

Answer 38

Min of 400 seeds, divided into 4 or more separate tests. Petri dish test, rolled-towel test, etc Seed sanwhiched between two layers of absorbent material Placed in a germinator at optimum conditions count # of seeds germinated

Question 39

Tetrazolium test- colorimetric test

Answer 39

Tetrazolium is coloress. When reduced by H ions, it turns red (changes to formazan) When viable seeds imbibe water, H ions are released as dehydrogenasses become active. Viable seeds become red Dead seeds remain colorless

Question 40

Calculation for % pure live seed

Answer 40

% PLS= % germination x % purity

Question 41

Hypogeal emergence

Answer 41

cotyledon(s) stay below the surface (better)

Question 42

Epigeal emergence

Answer 42

Cotyledons emerge above the soil surface

Question 43

Describe the soil qualities important for good seedbed

Answer 43

1. well-drained: if too wet, the seeds rot 2. well aerated: provide O 3. good water holding capacity: provide adequate moisture 4. good tilth: good seed-soil contact 5. no crusting- crusting impedes emergence

Question 44

What factors affect depth of seedling

Answer 44

1. seed size: larger seeds have more food reserves and can emerge from deeper depths 2. Type of emergence: plants w/ epigea emergence need to emerge above soil to commence seedling growth 3. Soil type: heavy soil- seed shallower; light sandy soil- seed deeper 4. Depth of available soil moisture: related to soil type

Question 45

List ad describe the factors to be considered when determining seeding rate

Answer 45

1. Percentage of pure live seed 2. Plant's capacity for competition -large plants need more room - indetermindate cutivars need more space than determinate > Determinate will grow to certain point then stop and flower > Indeterminate will continue to grow but flower anytime 3. Cultural conditions - fertility levels - irrigation: higher seeding rates when crop will be irrigated (up to double the rate) - time of planting- plant at optimum time -row spacing

Question 46

list and describe the factors that affect crop stand

Answer 46

1. Plant factors - adapted to region, high genetic purity, free from contaminatns 2. environmental factors - adequate water, temp, oxygen, and proper light or dark conditons 3. management factors - sow seeds at proper time, at proper depth; well-prepared seed-bed; protect from disease, insects, and weeds