5Juvenile stage Phase length varies: Morphologies: Vegetative growth and unable to flower even if plant grows an environment for floweringa physiological state of plant before flower differentiationFlowering cannot be inducedplants often differ in appearance from the adult.Phase length varies:annual – shorter eg. Weed will be at juvenile stage 4-5 d after germinatedperennial – longer at juvenile stageeg. in certain shrubs up to 40yearsMorphologies:Simple primary leaf to trifoliate leavesbeans: adult – compound leaf; juvenile – simple leafleaves loberapid growthUsually, the basal part of tree is juvenility and the top is mature or adult in physiology.
6Methods to shorten juvenility Long-day treatment - shorten the juvenility form 5～10 year to 1 year of birchGrafting- speed up flowering of fruit crops in 2-3 year.GAs treatments- can induce flowering in juvenility of ivy, cypress and fir.
7Transitional stage Have both juvenile and mature tissue May revert back to juvenile if environmental conditions are right.Involves the transition of a vegetative meristem, producing leaves and stems, into a floral meristem, producing flowers.
8Flower Initiation and Development a. Irreversible change in which to bud (meristem) changes from growing vegetative tissue to reproductive tissueb. Improper conditions can cause flower buds to abort1. High temp2. Moisture stressc. Flowers can be induced naturally or through PGR (plant growth regulators)
9Maturity or reproductive stage Stage where plants are ready to flower.Flowering - ultimate expression of mature stateChanges influence by environmentEnvironment serve as expression changes regulatorChanges in physiology and morphologyTransformation of primodium of stem, leaf or vegetative part to primodium reproductive organOne way transformationMany plants produce flowers independent of environmental conditions
10Temperature – Vernalization Photoperiodism Light intensity Factors influence transformation of the juvenile into the mature:Temperature – VernalizationPhotoperiodismLight intensityDrought stressLow fertility levels (especially N)
11SenescensThe final stage in a plant’s life cycle a. May occur naturally or accelerated by environmental conditions including pathogenic attack b. Cell and tissues deteriorate c. Partial senescence is when plant organs age and eventually die d. Complete senescence is when the whole plant dies. Monocarpic plant – flowering and fruiting once Polycarpic plant – many times/repeat
13Flower ProductionFour genetically regulated pathways to flowering have been identified1. The light-dependent pathway2. The temperature-dependent pathway3. The gibberellin-dependent pathway4. The autonomous pathwayPlants can rely primarily on one pathway, but all four pathways can be present
15Autonomous PathwayThe autonomous pathway does not depend on external cues except for basic nutritionIt allows day-neutral plants to “count” nodes and “remember” node location
16Autonomous Pathway--Plants Can Count Upper Axillary Bud Released from Apical DominanceLower Axillary Bud Released from Apical DominanceIntact plantShoot removedReplacement shootShootremovedhere5 nodes*replaced13 nodes**nodes = leaf bearing node-Tobacco plants produce a uniform number of nodes before flowering - Upper axillary buds of flowering tobacco remember their position if rooted or grafted
17Autonomous Pathway--Plants Can Remember ShootremovedhereShoot Florally DeterminedShoot Not Florally Determineda.b.Intact plantRooted shootFloweringrooted shootNot-Florally Determined Plants are said not to remember...Florally Determined plants are said to remember
18Photoperiodism : the response of plant to flower to photoperiod (day length of 24h cycle) Julien Tournois (1910) – 1st found about LD in floweringGeorge Klebs (1918) – observe the function of LD in floweringGarner & Allard (1920) –found photoperiod ⇨relative duration of light and dark towards control flowering of certain crops. eg. tobacco – flowering once expose to short light period (SDP)
19Hamner & Bonner (1938) – phenomena night break where dark disturbance during day time are not/a bit effect but light disturbance during night time inhibit flowering (SDP) or initiate flowering (LDP)Dark time more function in determine reaction in photoperiod
20Flowering response of Japanese morning glory (left) and black henbane (right) todaylength of 24-hperiod.Note the prominentflowers (arrows) inJapanese morningglory under shortdays and in blackhenbane under longdays . Plants of eachspecies under bothphotoperiod regimesare of the same ageLong days Short days
21Plant types responsive to photoperiodism 1. Short day plant (SDP)The plant can only flower under day length shorter than its critical day length of 24 h cycle. eg. chrysanthemumsie. the critical day length to induce flowering must be less than some maximum.2. Long day plant (LDP)The plant can only flower under daylength longer than its critical day length of 24 h cycle. eg. Chinese cabbage, beet etc.ie the critical day length must be longer than a minimum
223. Day neutral plant (DNP) Without critical daylength, they can flower in any day length of 24h cycle, if other conditions are satisfied. eg. tomato, cucumber, egg plant and bean. After bred for long time , most of crops are not sensitive to day length, eg. early rice, spring soybean, spring maize and cottonCritical Day Period:It is the duration of the photoperiod or the dark period that ultimately determines whether the plant has to go through vegetative growth or to produce flowers. referred as the day length of 24h cycle - the shortest day length for LDP flower and the longest day length for SDP flower.
28* Plants measure the ratio of Pfr/Pr. LDP would flower when the ratio is highSDP would flower when the ratio is lowSince Pfr is labile and is broken down at night or reverts back to Pr - the longer the night, the lower the phytochrome (Pfr) content.Thus, phytochrome is like the sand in an egg timer; the relative amount of Pfr remaining at the end of the night would be an indication of the day length.
29Flowering in SDP: Flowering in LDP: Short day plants flower when the night period is long.In day light or red light, phytochrome red (Pr) is converted to phytochrome far red (Pfr). The conversion actually only requires a brief exposure to white or red light.In the dark, Pfr is slowly converted back to Pr. A long night means that there is a long time for the conversion.Under short day conditions (long night) at the end of the night period the concentration of Pfr is low.In SDP, low Pfr concentration is the trigger for flowering.Flowering in LDP:Long day plants flower when the night period is short.In day light (white or red) the Pr is converted to Pfr.During periods when the day light period is long but critically the dark period is short, Pfr does not have long to breakdown in the dark. Consequently there remains a higher concentration of Pfr.In LDP, high Pfr concentration is the trigger to flowering.
32Dark period more important in photoperiodism reaction because interruption during night will inhibit flowering in SDP but promote flowering in LDP In short day plants, Pr promotes flowering when Pfr suppresses it, when it is vice versa in long day plants.
33Leaves detected photoperiod (at least Flowering hormone?Leaves detected photoperiod (at leastone leaf must be present for the plantto fllower)The receptor of photoperiod is located within the leaf.Photoperiodism sensor - leaf budBuds produce flowersBud meristem changes from vegetative to flower growth
34Stimulus transferredCut off all leaves after expose to photoperiod inhibit floweringCut off all leaves hrs later promote floweringIn 2005 a substance, mRNA (FL mRNA) was finally isolated that was found to be moving from leaf to flower meristem.This mRNA provides a link between the phytochrome system (the receptor), its activation of genes in the leaf (mRNA synthesis) and the differentiation of the meristem into the flower structure.Florigen - name given to the proposed flowering "hormone“.
36Commercially importance Flower industry eg. Chrysanthemum – sdpSelection of variety/cultivar for vegetable and field cropsManipulating Flowering ResponseUse artificial light or dark to simulate daylength.Light at night to lengthen day.10 pm to 2 pm.Cover with black cloth to shorten the day.
37Temperature (T)Vernalization ⇨ the process by which flowering is promoted by prolonged exposure to the cold of a typical winterplant expose to low T to initiate and promote floweringcommon in biennials and some perennial plantsreactions are varies among spesies/variety
39eg. apple, cherry, pear, peaches carrots, cabbage,bulbs like tulip, oniona. cold storage is used to preserve (sets) bulbs during winter this causes the sets to flower and produce seed in springb. to devernalize- sets are exposed to 27oC for 2-3 weeks before planting
40Temperature 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 wheatTypes temperature range(℃ ) daysSpring wheat ～ ～8Semi winter wheat ～ ～15Winter wheat ～ ～45
41Kinetics of the vernalisation • effective on actively growing plant.ie. growing plant – under gone vegetative stage, seed stage (annual) or bulb- Seeds must imbibed water (50% of seed dry weight) and the germination process has been initiated and exposed to low temperature ( vernalized). The vernalized seeds are dried and stored.- other plants in particular the biennial eg. cabbage, must reach a certain minimum size or age before they can be vernalized ie. whole plant• In general, the plant flowering need long day period and higher temperature after finishing vernalization, which induces flower differentiation
42The site/part of vernalization is the growing point (shoot apex) eg. celery- shoot apex exposed to low temperature, other part of plant to normal (higher) temperature, the plant can flower.-shoot apex to normal (higher) temperature, other part of plant low temperature, the plant remain vegetative• The main part sensitive to low temperature is shoot apical meristem - bud, apex meristems
43Facultative (quantitative) Flowering will appear earlier (faster) once expose to low T eg. winter annual cerealAbsolute (obligate)MUST expose to low T then flowering appear eg. biennial plants (cabbage)Exposure to desired period
44Lang (1957) found that GA function = vernalin, where GA promote flowering without vernalisation Vernalin hypothesis: After passing vernalization, plant can form vernalin,which can transfer from one part to others and promote flower.Vernalization only act the meristem of shoot apex. The effect can transfer form the cell to cell, not from organ to organ.
45Low T vernalization and GA3 induce flowering in carrot Control GA Low T
46- may be herbaceous or woody In relation to flowering and fruiting or duration of plant life, plants are group into:Perennial plantsAble to flower and produce seeds and fruit for an indefinite number of growing seasons- may be herbaceous or woody-in deciduous plants all the leaves fall, and the tree is bare, at a particular time of year-in evergreen plants, the leaves drop throughout the year, and so the plant is never completely bareAnnual plantsGrow, flower, and form fruits and seeds, and typically die within one growing season- usually herbaceousBiennial plantsHave two-year life cycles-they store energy the first year and flower the second year
47Application of vernalization on production 1. Treatment with vernalization and devernalization eg. onion for seed production 2. Induced crops to flower: forcing plants for earlier or late bloom blooms indoor 3. Selecting sowing date different types and characters
48Interaction bet. T and photoperiodism SDP initiate flowering at low T. eg. ChrysanthemumAs supplementary or complimentary to each other
49Devernalisation Vernalisation cancellation Before finishing vernalization, the effect will lost under high temperatureDevernalization - 25～40℃。eg. vernalized onion bulbs expose to high temperature after vernalisationDirect planting floweringKeep in warm temperature (2-3wks) not flowering
50NutritionKlebs (1918) – ratio of carbohydrate with inorganic nutrient esp N (C:N) high – will promote floweringKraus & Kraybill (US) – flowering on tomato plants was controlled by CHO:N levelCHO:N low – delay flowering & less flower (N high)CHO low, N low – less vegetative part, less flowerCHO:N high – faster and no of flower increase there is no C:N critical for flowering