Effects of Climate Change on Mechanisms That Initiate Flowering

1. Effects of Climate Change on Mechanisms That Initiate Flowering Donald Geiger University of Dayton Marianist Environmental Education Center

2. Basis For Study of Flowering Phenology • Exposure to warm temperatures over time is the main driver for springtime plant development, particularly for perennial plants in temperate zones. • Plants require a certain amount of exposure to warm temperatures before leaf out or flowering can occur. • The required heat sum,a quantified requirement that controls development, is a genetically controlled adaptive trait. • One of the most obvious ways ecosystems are affected by global climate change is through alteration of organisms’ developmental timing, their phenology. • Onset of flowering is an important element of phenology.

3. Climate Change and Flowering Phenology • The effect of climate change on the phenology of flower initiation was reported in the following publication: McEwan RW, RJ Brecha, DR Geiger, GP John 2011 Flowering phenology change and climate warming in southwestern Ohio. Plant Ecology 212,(1) 55-61. • The above study, based on observations of first flowering dates for an array of species from 1976 to 2003, provided evidence that climate change is affecting plant development.

4. Effect of Climate Warming on Flowering Phenology Development Development Quantitative L-D Statisticaly not earlier. Development Woody Ornamental Quantitative L-D Development Woody Fruit Development Quantitative L-D Development Qualitative L-D Spring Eph SpringEph In spring In summer Change in first flowering date over a 28–year (1976 to 2003) observation period in southwestern Ohio, USA. Change in flowering date represents the slope of the linear regression between first flowering date and year. Darkened symbols represent slopes that were different from zero (P<0.05). Horizontal dashed line represents no change. McEwan et al. Plant Ecology (2011) 2112:55-61

5. Basis For Flower Phenology Studies • This study revealed a trend of progressively earlier flowering time for a number of species. • The two earliest flowering species showed the largest advance in flowering time; advance decreased with later flowering date. • Two species that bloomed in mid summer also had advanced flowering dates. • Flowering is known to be initiated by a number of different physiological mechanisms. • Hypothesis: The two clusters of advanced bloom dates may result from climate change acting on two different mechanisms that regulate initiation of flowering.

6. Physiology of Floral Induction:

7. Background: A Survey of Physiological Mechanisms of Flowering Phenology • In their discussion the authors of the flowering phenology paper “suggest that future work is needed that bridges the gap between pattern (plant phenology response) and process (plant development physiology) in relation to particular climatic cues”. • The study that follows is a survey of process… mechanisms that initiate flowering and investigates possible ways in which climate change may advance initiation mediated by these mechanisms… pattern.

8. Floral Induction Shoot Apex Phase Changes 4 3 • Shoot apical meristems have three developmental phases: • 1. Juvenile phase • 2.Adult vegetative phase • 3.Adult reproductive phase • 4. Flower formation 2 2 1

9. Shoot Apex Stages for Flowering Adult Reproductive state emphasis on developmental states • Floral evocation in the adult reproductive phase involves three states on the way to flowering: • Competent- Shoot apex becomes competent to respond appropriately to a given developmental signal. E.g.- able to respond to photoperiod • Determined-able to follow some developmental program even if shoot is removed from its normal position and nurtured by grafting or rooting. E.g.- able to respond to plant growth regulator. • Expressed-apical meristem undergoes physiological steps that lead to morphogenesis to become a flower. (Process on slide 10)

10. shoot apex bract etal Vegetative shoot apex a. Signal to apex in determined state c. epal stamen primordia shoot pex b. d. Floral Induction and Development of the Flower 10

11. Survey of Factors Involved In Altering Flowering Time

12. Biochemical Signaling Is Able To Initiate Flowering • Mikhail Chailakhyan in 1937 demonstrated that floral induction can be transmitted through a graft indicating that a signal substance is being sent. • The hypothetical substance was named florigen. • In 2005 an RNA was mistakenly identified as florigen. In 2007 the paper was retracted; In 2008 florigen was found to be a protein a translocated floral initiation signal, florigen. • Florigen proteinsFT , Hd3a and PIF4 have been identified as biochemical signals known to be translocated to the apical meristem and to initiate flower formation. 12

13. Biochemical Signaling Involved in Flowering Mitigating factors: Flowering is expressed by action of the florigen signal in response to photoperiod or warming stimulus. Multiple development pathways for floral evocation in Arabidopsis. Part 2

14. Some Factors That Initiate Flowering: Candidates for Climate Responses • Temperature- warming after chilling • Temperature- vernalization = period of chilling • Photoperiod- day length; dark period length • Biennial life cycle- vernalization followed by lengthening days • Carbohydrate pathway- sucrose • Plant growth regulators- gibberellin, ethylene pathway- • Autonomous initiation- age, size, leaf number. • Significance:- Existence of multiple pathways provides flexibility to produce seeds under a variety of conditions. • Which of these mechanisms are affected by climate change?

15. Photoperiodism: Monitoring Day Length Day long enough Night long enough “day” too long “night” too short Long-Day plants Short-Day plants Photoperiodic regulation of flowering showing effects on short-day plants and long-day plants. Bar graphs show the effects of the duration of dark periods on flowering; data show the critical variable is length of the dark period.

16. Biochemical Signaling Involved in Flowering [pp 660 – 667] Long Day Short Day Determined by warming signal • Florigen gene expression regulated by warm temperature . PIF4 protein, a florigen Determined by photoperiod signal FT protein, the “florigen” is transported to the shoot apex to evoke flowering. 16

17. Case Studies of Flower Types: 1. Warming Activates Florigen Gene

18. Warmth Activates Flower Initiation • A period of warming over a period of time drives spring flower development, particularly for perennial plants in temperate zones. • Plants require a critical amount of exposure to warm temperatures before leaf out or flowering can occur; required heat sum (RHS) • RHSfor spring development is a genetically controlled, adaptive trait. • Enables plants to survive unpredictable early onset of warmth at the start of the growing season that does not persist. • Warmth activates PIF4 gene which acts as a florigen; exertscontrol over the flowering pathway (slide 16). • This mechanism is likely to be encountered in a number of species of plants but has not been studied extensively since its recent discovery (Kumar et al. 2012).

19. Mechanisms That Can Modulate Flowering Time • The thermal control time can be modulatedby conditions that affect the rate of accumulation of the required heat sum. RHS • Different environments may cause plants to require more or less time to accumulate the effective heat sum under the same input rate. • Conditions known to modulate RHS mechanism include: • snow pack depth photoperiod winter cold treatment • For example, photoperiod can delay bud break, protecting against responding to the threat of unusually early but intermittent warm temperature. This effect can complicate RHS/flower induction studies. • .

20. Case Studies of Flower Types: 2.Spring Ephemeral Pattern- Altered Rate of Flower Development

21. Spring Ephemeral Flowering Cycle • Spring ephemerals are species that have an active spring growth period limited to 40 - 60 days… adapted to take advantage of a two-month high-light before canopy closure. • Examples: fawn lily, Dutchman’s breeches, crocus,bleedingheart,snow drops, tulip, hyacinth, Cardaminespp (red = reported in McEwan et al.) • Annual life cycle, Erythroniumamericanum- yellow fawn lily 19 April 20 April 21 April 22 April 17 April Background: Spring Ephemerals

22. Spring Ephemeral Developmental Life Cycle Diagramic life cycle of Erythroniumamericanum. The perennial organ is shown in radial section to show bud development 5 2 3 4 6 7 1 Bud winter autumn spring summer 40 to 60 days above ground Soil temperature drives life cycle development that determines flowering time.

23. Spring Ephemeral Life Cycle • Species that have a 40 to 60 day growth period in spring. • Annual life cycle, Erythroniumamericanum-yelllow fawn lily • Dormancy is broken in autumn; bud and root growth continues through the winter at a very slow rate due to the low soil temperatures. (stages 2, 3). • As the soil warms shoot expansion is rapid (stages 3, 4), the long underground growth period ends and the above ground phase begins. This process is hastened by the warming due to climate change. • Sexual reproduction takes place over a 5- to 6-day period (stages 4,5,6) • Senescence of the above ground plant (stage 6) followed by senescence of the root (stage 7) and a stage of apparent dormancy of the perennial organ • stage 1)… the end of the 40 – 60 day period.Review previous slide. • Flowering time was advanced in crocus (Crocusflavus) and bleeding heart (Dicentraspecta sp.)the study of phenology affected by climate warming (McEwan et al. 2010). next year

24. Case Studies of Flower Types: 3. Flower Bud Dormancy Broken by Spring Chilling; Woody Perennials and Geophytes

25. Breaking of Bud Dormancy: Chilling • For a wide range of spring flowering perennials a temperature signal typically breaks dormancy of the renewal (winter) buds. • Renewal or winter buds form in early summer after leaf development ends and initiate next spring’s flowering. • In woody perennials (apple) formation next year’s leaf and flower primordia occurs in this year’s renewal buds in fall and early winter. !!! • Flowering is initiated by chilling during spring warming period. • Ex. Woody ornamental:- rhododendron; tree fruit species:- apple, pear • Flowering time was advanced in apple (Malusdomestica) in the study of phenology affected by climate warming (McEwan et al. 2010) • In the geophytes renewal buds form on the roots; flowering is initiated by chilling during the spring warming period. • Ex. Geophytes:- tulip, peonie

26. Breaking of Bud Dormancy: Chilling • In woody perennials breaking of bud dormancy in spring is a factor determining the timing of flowering... Example apple, pear • Bud dormancy in fall is initiated by low temperatures and short photoperiod. Fruit trees • In spring bud dormancy is broken by environmental signals, especially chilling during the spring warming period. • Linear accumulation of chilling hours occurs below 7o C. 45o F. • Short photoperiod promotes blooming. • Phenology of spring woody perennial flower activation is complex and still not well understood. • Remember: flowers formed in late fall, early winter in woody perennials. It is bud break that determined flower activation.

27. Case Studies of Flower Types: 4. Flowering in Qualitative, Obligate Long-Day Plants

28. Qualitative Obligate Long-Day Plants • Annual Phlox (Phlox drummondii) is a qualitative long-day plant. • qualitative L-D plant:- flowers ONLY on long days… obligate;day period must be at least a certain critical length to initiate flowering • quantitative L-D plant:- flowering ACCELERATED by long d. ; facultative:- long days are not required for flowering. • Under long-day conditions leaf processes mediated by phytochrome produce florigen that initiates flower formation by the apical meristem. (Revisit slides 16, 15, and 10) • At 11 hrD- 98 days to flowering; 13 hrD 87 d, 15 hrD75 d, 17 hrD74 d • In Phlox drummondiflower development did not increase beyond 15hr day. • Flowering time was advanced in annual phlox (Phlox drummondi) in the study of phenology affected by climate warming (McEwan et al. 2010) 28

29. Case Studies of Flower Types: 5. Flowering in Quantitative Facultative Long-Day Plants

30. Effect of Photoperiod and Temperature on Flowering in Quantitative L-D Plants • Shortest time to flowering in Ranunculus asiaticuswas achieved under 16 hr photoperiod at 16oC . • A quantitative (LD accelerates flowering), facultative (LD not required) long day plant • Both increased temperature + longer daylength reduce time to flowering. • The decreased time to flowering by lengthening the photoperiod was due to warming advancing development triggered by photoperiod induction of flowering. Ranunculus is a quantitative long day plant. A day of a certain length is not required for flowering to occur.

31. Effect of Photoperiod and Temperature on Flowering in Quantitative L-D Plants • Control of time to flowering in Viola: • Progress to flowering increases with temperature up to 28oC. • This pattern promotes earlier flowering as a result of higher springtime temperatures. • Progress to flowering also increases with daylength. • Not a photoperiod induction of flowering but the requirement pattern for growth of a quantitative long day plant. • Response to longer photoperiod is adaptive, lessening the lag imposed by cooler early season temperatures. • .

32. Effect of a Variety of Factors on Timing of Flowering in in Quantitative L-D Plants • A quantitative long-day plant but long photoperiod is not used as a cue. Lengthening days promoter stem elongation. • Flowers are formed underground during the previous winter or earlier when the plant forms its ramets. • In mountainous habitats the first date of bareground in spring is a good predictor of first flowering date, reminiscent of the winter/spring maturation of the developing flower stalks.. • Working hypothesis: increasing soil temperature promotes the formation and maturing of flowers initiated with the formation of ramets in the previous fall/winter.

33. Case Studies of Flower Types: 6. Flowering in Biennials

34. Biennial Sugar Beet Flowering • Biennials: First year rosette of sugar beet is unable to form reproductive shoots during the first year of growth. • Duplicate genes BvFT1 and BvFT2, homologs of the FT gene mediate regulation of flowering time: BvFT2promotes while BvFT1represses. • Winter vernalization lowers expression of BvFT1, which renders shoots competent to reproduce. • Exposure to lengthening days (quantitative long day) upregulatesBvFT2 and maintains BvFT1 in downregulated state. • Subsequent exposure to increasing day length (qualitative long day) causes the shoot to become determined. • The dependence on LD puts flower induction outside the springtime window of earlier increased temperatures.

35. Case Studies of Flower Types: 7. Flower Initiation Part of a Genetically Determined Development Program

36. Flowering Initiated At a Specific Development Stage • Some species of plants initiate flowering at a specific node (leaf location on the stem). • For a certain variety of cotton it occurs just after nodes number 5 or 6. • The program development is driven by heat measured in heat units. (next slide) • Determination by stage of plant development seems to be a common mechanism. 1st Flower Node 5 Node 6 Node 4 Node 3 Node 2 Node 1 Vegetative Branch Main Stem

37. Flowering Initiated At a Specific Development Stage Table 1.The average number of days and heat units required for various growth stages of cotton in the Mid-South. Modified from Oosterhuis, D.M. 1990. Growth and development of the cotton plant. In: W.N. Miley and D.M. Oosterhuis (eds) Nitrogen Nutrition in Cotton: Practical Issues. Proc. Southern Branch Workshop for Practicing Agronomists. Publ. Amer. Soc. Agron., Madison, WI Daytime high °F + Nighttime low °F -60 = DD60 2

38. Flowering Initiated At a Specific Development Stage • Species that initiate flowering at a specific stage of development that is promoted by spring warming would advance flowering as a consequence of climate warming. • Species that flower in early spring would be most reliably advanced due to climate warming. Those blooming later likely would show more variability. • For tomato plants, the first flower is initiated at node 6 to 8 depending on the earliness of the variety. In a commercial variety of tobacco the first flower was reported to occur at or about node 41. • In the phenology study Ageratum, Centauria, Dicentra, Hemerocallis, and Hosta flowering appears to be regulated by developmental stage.

39. Summary: Possible Mechanisms for Responses of Flowering To Climate Change

40. Flowering Phenology and Climate Warming • McEwan R, R Brecha, D Geiger, G John 2011 Flowering Phenology Change and Climate Warming in Southwestern Ohio. Plant Ecol212: 55-61. • Global climate change affects timing of plant development. • Thirty years of annual botanical surveys were used to examine impacts of climate change on plant development. • Authors of the study found a significant relationship between warming winter and spring temperatures and first flowering time for 60% of the species studied.

41. Effect of Climate Warming on Flowering Phenology Development Development Quantitative L-D Statisticaly not earlier. Development Woody Ornamental Quantitative L-D Development Woody Fruit Development Quantitative L-D Development Qualitative L-D Spring Eph SpringEph In spring In summer Change in first flowering date over a 28–year (1976 to 2003) observation period in southwestern Ohio, USA. Change in flowering date represents the slope of the linear regression between first flowering date and year. Darkened symbols represent slopes that were different from zero (P<0.05). Horizontal dashed line represents no change. McEwan et al. Plant Ecology (2011) 2112:55-61

42. Seven Flower Induction Mechanisms • 1. Warming activates florigen gene. • Arabidopsis thaliana; newly discovered; not researched • 2. Spring ephemeral pattern of flower development. • Erythroniumamericanum, Cardaminesp., Galanthussp., Allium sp., Anemone sp., Crocus sp. • 3. Flower bud summer dormancy broken in spring by chilling. • Woody trees and shrubs: Malus sp. Rhododendron sp. • Geophytes: Paeonia, Tulipa • 4. Long days requiredin qualitative, obligate long-day plants • Phlox sp. • 5. Long days accelerate flowering; quantitative L-D plants • Ranunculus asiaticus, Viola sp, Delphinium sp. • 6. Biennial species, chilling periodand lengthening days • Beta vulgaris • 7. Development + warming hastens flowering. • Dicentra, Hemerocalis, Hosta

43. Advanced Mar 2:Galanthussp.- Spring ephemeral Mar 6: Crocus flavus- Spring ephemeral Apr 18: Viola pubescens- Quantitative L-D plant; LD? + warming Apr 19:Malussp.- Woody fruit, bud dormancy broken by chilling Apr 25: Delphinium consolida- Quant. L-D plant; LD? + warming Apr 27: Dicentraspectabilis- Quant L-D plant; LD? + warming May 19:Hemerocaluslilioasphodelus- Development;Dev + warm Jul 14:Phlox sp- Qualitative, long-day plant; LD + warming Aug 11: Hostaplantaginea- Development;Dev + warm

44. Did Not Advance Mar 27: Forsythia sp-Flower bud dormancy broken by chilling. Apr 23: Ajugareptans- Development ?? Apr 27: Geranium maculatum- facult L-D plant; LD + warming May 5: Ranunculus sp- Development May 13:Centaureacyanus- Development Aug 8: Ageratumsp- Development

45. References [Pg 1] • Flowering physiology • Taiz L, E Zeiger 2006 Plant Physiology 4th Ed. Sinauer Associates Inc. • Zeevaart, JAD. 2008 Leaf-produced floral signals. Current Opinion in Plant Biology 11:541–547. • McDaniel CN, SR Singer and SME Smith. 1992 Developmental states associated with the floral transition. Developmental Biology 153:59-69. • Flowering phenology and climate warming • McEwan RW, RJ Brecha, DR Geiger, GP John 2011 Flowering phenology change and climate warming in southwestern Ohio. Plant Ecology 212,(1) 55-61. • Conover D, S Pelikan 2010 Earlier flowering in a restored wetland-prairie correlate with warmer temperatures (Ohio). Ecological Restoration. 28(4) : 428-430. • Bertin RI 2008 Plant phenology and distribution in relation to recent climate change. J. Torrey Bot. Soc. 135, 126–146. • Lapointe L (2001) How phenology influences physiology in deciduous forest spring ephemerals. PhsiologiaPlantarum 113:151-157 • Bradley NL, AC Leopold, J Ross,. W huffaker 1999 Phenological changes reflect climate change in Wisconsin. Proceedings of the National Academy of Science USA 96:9701-9704 • Floral induction mechanism triggered by warming • Kumar SV, Lucyshyn D, Jaeger KE, Alos E., Alvev E, Harberd NP, Wigge PA. 2012 Transcription factor PIF4 controls the thermosensory activation of flowering Nature March

46. References [Pg 2] • Release of bud dormancy in woody perennials • Arora A, Rowland LJ and Tanino K 2003 Induction and release of bud dormancy in woody perennials: a science comes of age. Hort Science 38:911-921. • Photoperiod and flowering phenology • Karlsson, M 1996 Control of Ranunculus asiaticusflowering by photoperiod and temperature. Hort Science 31:680-68 • Adams SR, Pearson S and Hadley P 1997 The effects of temperature, photoperiod and light integral on the time to flowering of Pansy cv, Universal Violet. Annals Bot 80;107-12. • Baloch J, M Munir, M Abid and M Iqbal. 2011 Effects of different photoperiods on flowering time of qualitative long-day ornamental annuals. Pakistan J Bot.43(3): 1485-1490. • Modulation of flower induction mechanisms • Inouye et al. 2002 Oecologica 130:543-550 investigate the roles of snowpack, frost, La Nina, climate change in modulating response. • Genetic and physiological bases for phenological responses to climates • Wilczek AM,LT Burghardt, AR Cobb, MD Cooper, SM Welch, J Schmidt 2010 Genetic and physiological bases for phenological responses to current and predicted climates. Phil Trqns R Soc B 365 (1555): 3129-3147.