Chapter 8 Flowering and reproductive physiology in plant

Section 1 JuvenilityJuvenility(幼年期) is an age or a physiological state of plant before flower differentiation, in which it is unable to flower, even if plant grows an environment for flowering.

“童期” of fruit trees.

• 1.1 Characteristics of juvenility• Flowering can not be induced.• Phase length Varies form only 1 year in certain

shrubs up to 40years in beech(山毛榉).• Morphologies:• Simple primary leaf to trifoliate leaves• Needlelike leaf to scalelike leaf (鳞片状叶)• Stems :creeping vine to shrublike

Usually, the basal part of tree is juvenility and the top is mature or adult in physiology.

• 1.2 The methods to shorten juvenility• (1) Long-day treatment shorten the

juvenility form 5～10 y to 1 y of birch(桦树).

• (2) grafting makes lots of fruit trees flowering in 2-3 y.

• (3) GAs treatments can induce flowering in juvenility of ivy，cypress (柏) and fir.

• Section 2 Vernalization• Vernalization 春 化 ( 作 用 ) refers low-

temperature promotion of flowering.

• After seed germination, the germinating seed (seedling) is treated with low T and sown in the warm field. The plant can flowers in summer day, which is called vernalization at early time. Now every response of plant life cycle to low T is called vernalization.

• Vernalization-required plants :winter annuals，wheat，barley and rape etc. most of biennials: carrot ,beet, celery and black henbane(天仙子) as well as some perennials: carnation

• 2.1 Characteristics of vernalization• 2.1.1 Temperature and time of vernalization• -4℃—12℃。Most efficient 1～2℃。• Reaction between temperature and time: In the range of

vernalization temperature, The lower T, the shorter time.• The lower temperature for vernalization the plant needs,

the longer time lasts.• Table 8-1 Temperature and time for vernalization of wheat• Types temperature range(℃ ) days• Spring wheat 5～15 5～8• Semi winter wheat 3 ～ 6 10～15• Winter wheat 0 ～3 40 ～45类型

• 2.1.2 The part sensitive to low temperature•• Celery test• shoot apex-------low temperature, other part of plant------

normal (higher) temperature, the plant can flower. • shoot apex------- normal (higher) temperature, other part of

plant------ low temperature, the plant can flower

• The main part sensitive to low temperature is apical cone of stem (shoot apical meristem).

• All tissue whose cell can divide response to low temperature and pass through vernalization . 。

• 2.1.3 The stage sensitive to low temperature• A vernalization treatment is effective only

actively growing plant. Cold treatment or dry seed will not suffice. Thus winter cereals may be vernalized as soon as the embryo has imbibed water and the germination process has been initiated (种子春化).

• Other plants, cabbage and Hyascramus in particular the biennial, must reach a certain minimum size before they can be vernalized (绿体春化) ,

• In general, the plant flowering need long day period and higher temperature after finishing vernalization, which induces flower differentiation.

Effect of low temperature and long day on henbane

• 2.1.4 Devernalization• Before finishing vernalization, the effect will

lost under high temperature-----devernalization25～40℃。

• 2.2 Mechanism of vernalization• 2.2.1 Metabolism induction hypothesis :• Vernalization only act the meristem of shoot

apex. The effect can transfer form the cell to cell, not from organ to organ.

High TLow T

Scion treated with low T

Stock in high T Stock treated with low T

Scion in high T

Test1. Vernalization can not transfer form one branch to another

• 2.2.2 Vernalin hypothesis• After passing vernalization, plant can form

vernalin,which can transfer from one part to others and promote flower.

• Ⅰ（LT） Ⅱ（LT）• Precursor →Mediate →Florigen

• ↓Ⅲ（HT）• Degradation (devernalization)

Test2. Vernalization can transfer form one branch

High TLow T

Scion treated with low T

Stock in high T Stock treated with low T

Scion in high T

• Gibberellic acid (GA3)？• LT

• [3H] kaurenoic acid [3H] GA9

•• without [3H] GA9

• Gibberone？• SA？

HT

Normal GA3 LT

Low T vernalizationand GA3induce flowering in carrot

0

50

100

150

200

0 2 3 4 5 6 7 8 9

茎长CM

Vernalzation

GA3

0

5

10

15

20

25

30

0 0 1 2 3 4 5 6 7 8 9

周数

开花节数

Vernalzation

GA3

The difference in flowering and stem elongation of Scrophylariavernalis induced by vernalization and GA treatments

2.2.3 Some genes relevant to vernalization

• Arabidopsis thaliana：fca——late flower,• vrn1,vrn2——genes responsive to LT，

fy,fpa,fve,fca,fe——genes sensitive to vernalization.

• Spring wheat：vrn1,vrn2,vrn3,vrn4,vrn5——genes sensitive to vernalization.

• 2.4 Application of vernalization on production• (1) Treatment with vernalization and devernalization：

Sowing winter wheat in spring，devernalization for angleca (当归)、onion.

• (2) Selected sowing time ： different types and characters

• (3) Induced crops： satisfy low temperature for vernalization

• Section 3 Photoperiodism• Photoperiodism：The response of plant flower

(development) to photoperiod (day length of 24 h cycle)

Long

day

s

Sh

ort d

ays

Pharbitis nil (Japanese morning glory)

Hyoscyamus niger(black henbane)

Flowering response of Japanese morning glory (left) and black henbane (right) to daylength of 24-h period.

Note the prominent flowers (arrows) in Japanese morning glory under short days and in black henbane under long days . Plants of each species under both photoperiod regimes are of the same age.

• 3.1 Plant types responsive to photoperiodism

• 3 basal types for photoperiodism：SDP、LDP and DNP。

• 3.1.1 Short day plants, SDP• The plant can only flower under daylength shorter

than its critical day length of 24 h cycle.• Such as morning glory( 牵 牛 ), cocklebur( 苍 耳 ),

chrysanthemums, tobacco, late soybean, late rice and late maize.

• They usually flower in autumn or early spring.

• 3.1.2 Long day plants,LDP• The plant can only flower under daylength

longer than its critical day length of 24 h cycle.• Such as wheat, rye, henbane, beet,carrot etc.• They usually flower in spring end or summer。

• 3.1.3 Day-neutral plants, DNP (日中性植物)

• Without critical daylength, they can flower in any day length of 24h cycle, if other conditions are satisfied.

• Such as tomato, cucumber, egg plant and bean.• After bred for long time , most of crops are not

sensitive to day length, Such as early rice, spring soybean, spring maize and cotton.

• 3.1.4 Critical day(CD,临界日长)• CD is referred as the day length of 24h cycle is

the shortest day length for LDP flower and the longest day length for SDP flower.

Critical days of some SDP and LDP Plants CD(h) Plants CD(h)

Short day plants Soybean cv. Madelin

cv. Beijing

cv.Bilockxi

Rice

Chrysanthemums

Morning glory

Xanthium

Sugarcane

17 15

13～1412～15

15 15

15.5 12.5

Long day plants Barley

Wheat

Spinach

Beet

henbane

10～14

>12 13

13～14 11.5

0

20

40

60

80

100

120

0 5 10 15 20 25

Daylength（h）

Flower（

%）

SDPLDP

DNP

Test for LDP、SDP and DNP

CD-SDPCD-LDP

• 3.1.5 Other types responsive to photoperiodism• (1) Intermediate-day plants• (2) Long-short day plants• (3) Short-long day plants• (4) Terminal day plants

• 3.2 Characteristics of photoperiodism• 3.2.1 Function of dark and light periods• （1）The role of dark length

LDP SDP

NF F

F NF

F NF

F NF

F NF

F F

F-flowering; NF-not flowering

24h

36h

16h

Darkness-broken experiment gives conclusion that dark-length decide the flower formation.

Scientific definition：

LDPs are short night plants, which flower under the night length shorter than their critical night length of 24h cycle.

SDPs are long night plants，which flower under the night length longer than their critical night length of 24h cycle.

Critical night length?

R NF F

SDP LDP

R+FR+R NF F

R+FR F NF

R+FR+R+FR F NF

The reversed effects of red light (R） and far red light （FR）on flower

• （2）、Effects of light duration on flower：• Increase the number and quality.（Fig 8-9，8-

10。）

• 3.2.2．Effects of temperature on floral：• LT results in LDP flowering in shorter daylength

and HT does SDP flowering in longer daylength.• Beet can flower in 8h daylength of 24h cycle at

10-18°C.• Tobacco needs flower short day at 18°C of night,

but, at 13°C, it can flower under 16-18h daylengthof 24h cycle.

• 3.3.3．Photoperiod induction• Plants can flower in both suitable or

unsuitable photoperiod conditions if it has got enough days of suitable photoperiod

0

20

40

60

80

100

120

0 1 2 3 6 9 10 12 14

开花%

紫苏

苍耳

SDP

0

20

40

60

80

100

120

0 1 2 3 6 9 10 12 14

开花%

天仙子

黑麦草

LDP

• 3.4 Mechanism of photoperiod induction• 3.4.1、Organ responsible to photoperiod stimuli

What part is sensitive to photoperiod?

不

• 3.4 Mechanism of photoperiod induction• 3.4.1、Organ responsible to photoperiod stimuli

Leaf sensitive to photoperiod stimuli。Functional leaf is more sensitive that senescing or youngest leaves.

不

• 3.4.2 Stimulus of floral---Florigen

SD

LD

Two branches of chrysanthemums flower, when only one branch in SD

Several plants flower by grafting, when only one leaf is induced in SD

Photoperiod-induced leaf promotes flower by grafting

(left) and the noninducedleaf promote vegetation

Successful transfer of the floral stimulus between different genera: The scion(right branch) is the LDP (Petunia hybrida), and the stock is nonvernali-zationed henbane. The graft combina-tion was maintained under LDs

• 3.4.3 Inhibitors of floral

SD

长日

Leaves under LD produce inhibitor and block flower in soybean.

短日

长日

Removing the leaves under LD stimulates flower in whole plant.

LD

• 3.4.4 Relationship between vernalization and photoperiodism

• Most of plants requiring vernalization belong to LDPs: Wheat, barley, spinach, sugarbeet, carnation.

• Chrysanthemums is LT-SD plant, and faba, pea are LT-DN plants.

• 3.4.5 Application of photoperiodism on production

• (1) Introduced crop（引种） . • The Northern Hemisphere: The law for the

inducing crops：• SDP induced from south to north, growth stage longer,

early matured cultivar can be done. On contrary, from north to south, growth stage shorter, lately matured cultivar can be done.

• LDP induced from south to north, growth stage shorter, lately matured cultivar can be done. On contrary, from north to south, growth stage longer, early matured cultivar can be done.

• (2) Select suitable sowing stage• SDP or LDP or DNP. Genetic male sterility

induced by daylength.

• (3)Regulation of flower time:• （a）Hybrids: Two parents flower at same

time (父、母本花期相遇).• （b）Flash flower production:• Early or late flower controlled by SD or LD.• SD treatment make chrysanthemums flower

early and darkness broken (extension of day time) results in flower late.

• 3.5 Characteristics of phytochrome• 3.5.1 Chemical characters• Phytochrome （ 1959 ） ——lettuce (Grand

Rapids).

•Two form: Pr----one form absorbing red light (660) and the other absorbing far red light (730)

Phytochrome is complex of chromophore and protein, and chromophore is consist of four pyrrole in line.

• In physiology Pfr is active form and Pfr is inactive form.

• However, plant flowering depend on the ratio of Pfr/ Pr.

• Higher ratio of Pfr/ Pr is advantage to LDP flower and lower ratio of Pfr/Pr is satisfied to SDP flower.

• 3.5.2 Physiological function and mechanism of phytochrome

• 3.5.2.1 Physiological effects :• Seed germination; De-etiolation ( 去黄化 ); Stem

elongation; Plumular hook opening; Leaf and cotyledon expansion; Chlorophyll synthesis; Chlorophyll development; Circadian clock; Photoperiodic floral induction; Sensitivity to phototropic stimulus; Enzyme activation; Gene activation /repression; Transmembrane potential; Anthocyanin synthesis

3.5.2.2 Mechanism of photochrome function

Phytochrome activity is modulated by phosphorlation status.

Following activation by red light, the phy-associated phosphatasePAPP5 and as-yet unidentified kinase modulated phy activity in response to the intensity or quality of light. (After ryu et al. 2005)

DICOT (A. thaliana) MONOCOT (O. sativa; Sorghum bicolor)

PHYA

PHYC

PHYE

PHYD

PHYB

VLFR (seed germination) FR-HIR (hypocotylelongation)

LFR (hypocotylelongation)

VLFR (seed germination) LFR (petiole elongation)

LFR (petiole elongation)

R-HIR (hypocotyl elongation) R-HIR (flowering) LFR (seed germination)

PHYA

PHYC

PHYB

VLFR (coleoptile germination) FR-HIR (brace root elongation)

unknown

LFR (mesocotylelongation)

Difference in phytochrome gene family structure and function in the dicot and monocots

Fig 19-4 Early flowering in the phyB mutant of Arabidopsis.

The two plants shown were grown together in long days for the same length of time. On the right is a wild-type plant that has not yet initiated a macroscopic inflorescence shoot. On the left is a phyB mutant with flower already evident at the tip of the shoot.

• Section 4 Morphology and physiology of floral formation

• 4.1 Changes in morphology and physiology of floral differentiation

• 4.1.1 Morphology

• Remarkable events: • Initial elongation of apical cone in monocots• Enlargement of apical cone in dicots

• 4.1.2 Physiology ：DNA replication

• 4.2 Sexual differentiation• 4.2.1、Dioecism (雌雄异株):• hemp(大麻), asparagus(石刁柏)

• Mulberry(桑树), spinach and willow.

• Little effect by environmental conditions，use them base on the aims.

• Male has some stronger metabolic pathway.

• 4.2.2、Monoecism(雌雄同株)：• A、Monocling(雌雄同花)：cotton、rice,

wheat. Impossible sexual change.• B、Dicling(雌雄异花)：• maize, cucumber, pumpkin and castor

• Plant hormones and environmental conditions can often control the sexual differentiation.

• Sufficient N and H2O, CO and C2H2 treatment, pinching ( 打顶 ) to favorite female.

• GA treatment，low N or H2O to favorite female.

• 4.3 Molecular models of flower development• Based on anatomy, genetics and molecular

biology, 3-4 gene families (ABC(D)) control flower structures: sepal, petal, stamen, carpel and ovule.

B

A C

1 2 3 4sepal petal stamen carpal

B

A C

1 2 3 4A 4B Sepal petal stamen carpal ovual

D

The model of 4 floral whorls for flower development

茎生叶

莲座叶

一次花序

Gynoecium:雌蕊群carpel: 心皮Anther: 花药Petal: 花瓣Sepal:萼片Placenta:胎座Ovule:胚珠

Fig 19.11 The anatomy of Arabidopsis flower

4. 3 Molecular models of flower development

Fig 19.16 The genes determine floral whorls

AP3/PI

ABCDE model

AP1/AP2 AGFB7/11

sep1,2,3

BA C

D

E

sepal petal stamen carpel ovule

Fig 19.15 The four original ABC mutants, ap2,ap3, pi and ag. Each mutant demonstrates a homeotic transformation.

Plant grown in short-day condition

4、4 The examples of some genes for flowering

CONSTANS(CO),

CO

AP2

Fig 19.5 CONSTANS(CO),a putative transcription factor with similarity to zinc-finger protein, expression increases in long days. RNA gel blot analysis indicates that seeding grow in long days (LD) show increased expression of flower-promoting gene,CO, which is expressed both in shoot and in the leaves. The expression of APETALA2 (AP2), however,is similar in long and shoot days (SD).

LD seedling

SD seedling

Fig 19.9 TFL1 regulates flowering and indeterminacy. (A) tfl1 inflorescence phenotype (right and enlargement) compared with wild type (left). Mutant plants terminate early in a terminal flower or a terminal cluster of flowers. (B) TFL1 is expressed in the center of the inflorescence meristem.

Fig 19.8 LEAFY(LFY), a gene for floral meristem identity, is necessary and sufficient to convert indeterminate shoots into flowers in Arabidopsis.(A) In lfy mutants, shoots that would normally develop as flowers are converted to indeterminate shoots. All of the secondary shoots shown here have emerged in the position in which flowers would develop on a wild-type inflorescence. (B) In a 35S:LFY plant that expresses LFY constitutively, secondary shoots are converted into flowers and the primary shoot terminates early in a flower or cluster of flower.

• Section 5 Physiology of fertilization• 5.1 Structure and germination of pollen• 5.1.1 Structure of pollen

Outer wall

Inner wall

Germmination pore

• 5.1.2 Structure of pollen (P)• Double wall: the outer with germination pore and• P recognizing proteins, the inner with hydrolases• Neuclei:vegetative neucleus (larger one) and • reproductive one (sperm)——2-cell(neucleus) pollen; • vegetative neucleus and 2 reproductive neuclei• (sperms)——3-cell(neucleus) pollen• Pollen fertility depends on sugar, starch and Pro and

pigment contents. The higher contents are better fertility. • Pollinated by insects——higher pigment contents• Pollinated by wind ——higher starch contents.

• 5.1.3 Recognition and fertilization• Rcongnition: A special reaction between

two cell to get some information for cell fusion.

• Fertilization:A process of anisomerogamy(雌雄配子结合). Fertilization depends oncompatibility (亲和性) between pollen and stigma (柱头).

• The proteins in outer wall of pollen undergo recognition substance as well as the proteins in the surface of stigma.

• If compatibility, the substance in the surface of stigma can induce pollen germination and pollen can produce hydrolase to make stigma hydrolysis. The pollen tuber elongates, pass through stigma and fertilizes.

• If incompatibility, the stigmatic pappillawill produce tylosis to black the entrance of pollen tuber or/and produce hydrolases(Rnase and protease) to degrade RNA and protein of pollen tuber and kill the pollens.

• Incompatibility in distant crossing often show that pollen tuber in stigma slowly elongates and does not reach to embryo sac.

• Self incompatibility is common in nature and about half of plants is incompatible, which are controlled by a serious multiple alleles. This incompatibility occurs when same S alleles exist in both male and female.

Fig 19.32 Genetics of self-incompatibility. (A) gemetophytic self incompatibility (GSI) and (B) sporophytic self incompatibility (SSI).

• 5.2 Factors affecting fertilization• 5.2.1 Vigor of pollen• Longevity of 3-cell(neucleus) pollen is less than 2-

cell(neucleus) pollen. Rice for 3-5min,wheat for 15-30min, maize for 1d, pear and apple for 70～210d。

• Just dissipated ripen pollen has highest vigor.• Pollen storage：dry, low temperature and low

oxygen (but gramineous needs higher than 40% of RH. ，T 1-5℃。

• Pollen germination and pollen tuber elongation show group effect：The more pollens on the stigma, the faster pollen germination, the longer tuber elongation and the easier fertilization.

• Competition and more ezymes.• Significant increase in yield of crop by

artificial pollination.

• 5.2.2 Viability of stigma• Vary in plant species, most of plants last more than one

weeks. But highest viability appears on flowering day.。• 5.2.3 Environmental conditions• (1) Temperature. Not high and low.• (2) Relative humidity. Middle• (3) Mineral nutrition. • B is necessary for germination and elongation

of pollen. • Sugar （5～25%） is required as nutrition

and osmotic regulator. •

• (4) Wind: pollination of some plants by aid of wind .

• (5) Insects pollination of some plants by insects

Section 7 Development of seed and fruit

7.1 Seed development

7.1.1 Embryogenesis

A process in which zygot initiates cell

division and forms embryo .

植物胚胎发生概述T—端细胞；B—基细胞；EP—真正胚；S—胚柄；BC—胚柄基部Pd—原表皮细胞；U —上层；I—下层；Hs—胚根原细胞；Pc—原形成层；Gm—基本分生组织；C—子叶；A—胚轴；MPE—珠孔端；CE—合点端；SC—种壳；En—内胚乳；SM——茎分生组织；RM—根

分生组织

• 7.1.2 Physiological changes during fertilizition

• (1) IAA rise in stigma. • (2) Respiration rise.• (3) stigma as a strong sink.

• 7.1.3 Physiological and biochemical events during seed development

• (1) Change in respiration

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 10 20 30 40

开花后天数（d）

呼吸

强度

（103ulO2/胚

）

• (2) Synthesis and accumulation of storage substance.

• （ a ） Starchy seeds: Soluble sugar accumulates at beginning, and starch increase and reach the highest in the end, while the soluble sugar decreases. 。

• （b）Oil seeds

Soluble sugar and starch accumulate at beginning and then fat accumulates while the farmer decrease.

• As ripening, iodine value of fat （100g of fat consumes grams of I2）rise, and the acid value （ micrograms of NaOH is used to neutralize 100g of fat ） deceases.

• This indicates that oil seed first synthesizes saturated fatty acid , then turn it into unsaturated fatty acid, first forms free fatty acid and then converse it to triglyceride.

• （c）Protein seed• During the ripening carbohydrate contents decrease (a

certain of carbohydrate even at late stage), amino acid and amide rise at first and decrease in the end, stored protein contents reach up maximum at ripen stage.

• （3）Plant hormones: Contents and type change from CTK—GA—IAA—ABA。

• （4）dehydration• At late ripening stage, water contents of seed

decline and resistance of seed to dehydration rise as Lea (late embryo abundant) protein, ABA and soluble carbohydrates accumulates.

• 7.1.4 Environmental factors influencing main components of seed

• Soil drought: The grain filling is not enough and protein contents was relatively high as starch contents decrease in great degree.

• Low temperature and difference in temperature between day and night are favor to synthesize fat and unsaturated fat acid.

• K and P can promote sugar transport, starch and fat accumulation. N can increase protein contents of products.

• 7.2 Fruit development• 7.2.1 Fruit growth• S shape and double S shape.

• Fruit develops from embryonic sac(胚囊), floral envelope (花被) or receptacle (花托) after fertilization, which is called seed-fruit .

• Banana is non-seed fruit due to parthenocarpy(单性结实) .IAA content is higher in non-seed fruit than in the seed fruit.

CKCK

部分受精

CK

Removing seed+100

Removing seed+100 ppm NAA

• 7.2.2 Physiological and biochemical events during fruit ripening

• (1) Change in respiratory rate——climacteric

-20

0

20

40

60

80

100

120

140

0 1 2 3 4 5 6 7 8 9 10

Time(d)

Relative value

CO2

ETH

ACC

• (2) Coloring :• Carotenoids and anthocyanins synthesize

and accumulate while chlorophylls degrade during the fruit ripening.

•

• (3) Sweet, good smell and less acid:• Starch to soluble sugar.• Volatile aromatic compounds increase• Organic acid oxidation. (0.1～0.5% better)

• (4) Austere loss and fruit softening• Tannin degradation or aggregation .• Protopectin degradation and starch dehydration.

• 7.2.3 Environmental conditions affecting fruit development

• (1)Water: deficient water results in slow growth and small fruit. Superfluous water causes fruit drop and less sweet, less aromatic.

• (2)Temperature: Fruit development is enhanced by greater difference in T between day and night. (3)Light: without enough light, fruit is smaller, low sugar contents and poor color.

HO

HOO—galactose（arabinose）

OH

OHA C

B+

HO

HOOH

OH

？

dark

Weak light

HO

HO

OH

OH

OH

强光

cyanidin

anthocyanin

The regulation of light to cyanidin synthesis

• (4)Mineral nutrition。 P,K increase fruit and seed and fruit sugar contents.