Plant Reproductive Physiology

1. Plant Reproductive Physiology

2. Flowering • Photoperiodism • Temperature • Nutrition

3. Fruiting • Pollination • Development after fertilization • Maturity, ripening and senescens

4. Plant Growth Stages • Juvenile stage • Transitional stage • Maturity stage • Senescence stage

5. Juvenile stage • 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.

6. Methods to shorten juvenility • Long-day treatment - shorten the juvenility form 5～10 year to 1 year of birch • Grafting- speed up flowering of fruit crops in 2-3 year. • GAs treatments- can induce flowering in juvenility of ivy, cypress and fir.

7. Transitional 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.

8. 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)

9. Maturity or reproductive stage • 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

10. Factors influence transformation of the juvenile into the mature: • Temperature – Vernalization • Photoperiodism • Light intensity • Drought stress • Low fertility levels (especially N)

11. Senescens The final stage in a plant’s life cycle a. May occur naturally or accelerated by environmental conditions includingpathogenic 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

12. Flowering

13. Flower Production 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. Autonomous Pathway 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. -Tobacco plants produce a uniform number of nodes before flowering- Upper axillary buds of flowering tobacco remember their position if rooted or grafted Upper Axillary Bud Released from Apical Dominance Lower Axillary Bud Released from Apical Dominance 13 nodes* replaced 13 nodes* removed 5 nodes* replaced 5 nodes* removed Shoot removed here Shoot removed here Intact plant Shoot removed Replacement shoot Intact plant Shoot removed Replacement shoot *nodes = leaf bearing node Autonomous Pathway--Plants Can Count

17. Shoot Florally Determined Shoot Not Florally Determined Shoot removed here Shoot removed here Shoot removed Shoot removed Flowering rooted shoot Flowering rooted shoot Intact plant Rooted shoot Intact plant Rooted shoot a. b. Autonomous Pathway--Plants Can Remember Not-Florally Determined Plants are said not to remember...Florally Determined plants are said to remember

18. Photoperiodism: the response of plant to flower to photoperiod (day length of 24h cycle) • JulienTournois (1910) – 1st found about LD in flowering • George Klebs (1918) – observe the function of LD in flowering • Garner & 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)

19. 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

20. 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

21. Plant 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. 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. iethe critical day length must be longer than a minimum

22. 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.

25. Photochrome The chemical nature of the receptor is a the molecule PHYTOCHROME. - biological compound that absorbs light Two types : -Phytochrome far red (PFR) -Phytochrome red (PR) - interconvertible

28. * 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.

29. 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.

32. 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.

33. 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

34. Stimulus transferred • Cut off all leaves after expose to photoperiod inhibit flowering • Cut off all leaves 20 -36hrs 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“.

36. Commercially importance • Flower industry eg. Chrysanthemum – sdp • 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.

37. Temperature (T) • 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

39. 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 27oC for 2-3 weeks before planting

40. 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

41. 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 inparticular the biennial eg. cabbage, must reach a certain minimum size or age before they can be vernalizedie. whole plant • In general, the plant flowering need long day period and higher temperature after finishing vernalization, which induces flower differentiation

42. 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

43. Facultative (quantitative) • Flowering will appear earlier (faster) once expose to low T eg. winter annual cereal • Absolute (obligate) • MUST expose to low T then flowering appear eg. biennial plants (cabbage) • Exposure to desired period

44. 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.

45. Low T vernalization and GA3 induce flowering in carrot Control GA3 Low T

46. 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

47. Application 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

48. Interaction bet. T and photoperiodism • SDP initiate flowering at low T. eg. Chrysanthemum • As supplementary or complimentary to each other

49. Devernalisation • Vernalisation cancellation • Before finishing vernalization, the effect will lost under high temperature • Devernalization - 25～40℃。 • eg. vernalized onion bulbs expose to high temperature after vernalisation • Direct planting  flowering • Keep in warm temperature (2-3wks)  not flowering

50. Nutrition • 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