Vegetative growth and unable to flower even if plant grows an environment for flowering a physiological state of plant before flower differentiation Flowering cannot be induced plants often differ in appearance from the adult. Phase length varies: annual – shorter eg. Weed will be at juvenile stage 4-5 d after germinated perennial – longer at juvenile stage eg. in certain shrubs up to 40years Morphologies: Simple primary leaf to trifoliate leaves beans: adult – compound leaf; juvenile – simple leaf leaves lobe rapid growth Usually, the basal part of tree is juvenility and the top is mature or adult in physiology.
1. Long-day treatment - shorten the juvenility form 5 10 year to 1 year of birch 2. Grafting- speed up flowering of fruit crops in 2-3 year. 3. GAs treatments- can induce flowering in juvenility of ivy, cypress and fir.
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.
Flower Initiation and Development a. Irreversible change in which to bud (meristem) changes from growing vegetative tissue to reproductive tissue b. Improper conditions can cause flower buds to abort 1. High temp 2. Moisture stress c. Flowers can be induced naturally or through PGR (plant growth regulators)
Stage where plants are ready to flower. Flowering - ultimate expression of mature state Changes influence by environment Environment serve as expression changes regulator Changes in physiology and morphology Transformation of primodium of stem, leaf or vegetative part to primodium reproductive organ One way transformation Many plants produce flowers independent of environmental conditions
Factors influence transformation of the juvenile into the mature: 1. Temperature – Vernalization 2. Photoperiodism 3. Light intensity 4. Drought stress 5. Low fertility levels (especially N)
The final stage in a plants 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
13 Four genetically regulated pathways to flowering have been identified 1. The light-dependent pathway 2. The temperature-dependent pathway 3. The gibberellin-dependent pathway 4. The autonomous pathway Plants can rely primarily on one pathway, but all four pathways can be present
15 The autonomous pathway does not depend on external cues except for basic nutrition It allows day-neutral plants to count nodes and remember node location
16 Upper Axillary Bud Released from Apical Dominance Lower Axillary Bud Released from Apical Dominance Intact plantShoot removedReplacement shoot Shoot removed here 5 nodes* removed 5 nodes* replaced Intact plantShoot removed Replacement shoot Shoot removed here 13 nodes* removed 13 nodes* replaced *nodes = leaf bearing node Autonomous Pathway--Plants Can Count - Tobacco plants produce a uniform number of nodes before flowering - Upper axillary buds of flowering tobacco remember their position if rooted or grafted
17 Shoot removed here Shoot removed here Shoot Florally DeterminedShoot Not Florally Determined a.a. b. Intact plant Shoot removed Rooted shoot Flowering rooted shoot Intact plant Shoot removed Rooted shoot Flowering rooted shoot Autonomous Pathway--Plants Can Remember Not-Florally Determined Plants are said not to remember...Florally Determined plants are said to remember
1. Julien Tournois (1910) – 1 st found about LD in flowering 2. George Klebs (1918) – observe the function of LD in flowering 3. Garner & Allard (1920) –found photoperiodrelative duration of light and dark towards control flowering of certain crops. eg. tobacco – flowering once expose to short light period (SDP)
4. Hamner & 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
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 Long days Short days
1. Short day plant (SDP) The plant can only flower under day length shorter than its critical day length of 24 h cycle. eg. chrysanthemums ie. 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
3. 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 cotton Critical 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.
The chemical nature of the receptor is a the molecule PHYTOCHROME. - biological compound that absorbs light Two types : -Phytochrome far red (P FR ) -Phytochrome red (P R ) - interconvertible
* Plants measure the ratio of Pfr/Pr. LDP would flower when the ratio is high SDP would flower when the ratio is low Since 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.
Flowering in SDP: 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.
Dark 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.
Flowering hormone? Leaves detected photoperiod (at least one leaf must be present for the plant to fllower) The receptor of photoperiod is located within the leaf. Photoperiodism sensor - leaf bud Buds produce flowers Bud meristem changes from vegetative to flower growth
Stimulus transferred Cut off all leaves after expose to photoperiod inhibit flowering Cut off all leaves hrs later promote flowering In 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.
1. Flower industry eg. Chrysanthemum – sdp 2. Selection of variety/cultivar for vegetable and field crops Manipulating Flowering Response Use 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.
Vernalization the process by which flowering is promoted by prolonged exposure to the cold of a typical winter plant expose to low T to initiate and promote flowering common in biennials and some perennial plants reactions are varies among spesies/variety
eg. apple, cherry, pear, peaches carrots, cabbage, bulbs like tulip, onion a. cold storage is used to preserve (sets) bulbs during winter this causes the sets to flower and produce seed in spring b. to devernalize- sets are exposed to 27 o C for 2-3 weeks before planting
Temperature and time of vernalization 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 Semi winter wheat Winter wheat
Kinetics 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
The 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
1. Facultative (quantitative) Flowering will appear earlier (faster) once expose to low T eg. winter annual cereal 2. Absolute (obligate) MUST expose to low T then flowering appear eg. biennial plants (cabbage) Exposure to desired period
Lang (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.
Control GA3 Low T
In relation to flowering and fruiting or duration of plant life, plants are group into: Perennial plants Able 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 bare Annual plants Grow, flower, and form fruits and seeds, and typically die within one growing season - usually herbaceous Biennial plants Have two-year life cycles -they store energy the first year and flower the second year
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
SDP initiate flowering at low T. eg. Chrysanthemum As supplementary or complimentary to each other
Vernalisation cancellation Before finishing vernalization, the effect will lost under high temperature Devernalization eg. vernalized onion bulbs expose to high temperature after vernalisation Direct planting flowering Keep in warm temperature (2-3wks) not flowering
Klebs (1918) – ratio of carbohydrate with inorganic nutrient esp N (C:N) high – will promote flowering Kraus & Kraybill (US) – flowering on tomato plants was controlled by CHO:N level CHO:N low – delay flowering & less flower (N high) CHO low, N low – less vegetative part, less flower CHO:N high – faster and no of flower increase there is no C:N critical for flowering