Plant Growth & Development

Plant Growth & Development
Responses to Internal & External Signals

Mix & Match Review: Ch. 39.1-2 1, 4, 7 2, 5, 8 3, 6 Etiolation
Reception Transduction Response Phototropism Gravitropism 1, 4, 7 Etiolation De-etiolation Leaf abcission (ethylene:auxin) Hormone ID all 7 key hormones 2, 5, 8 Expansin protein (auxin) Cytokinin protein (mitosis) Cytokin protein (apoptosis) Ripening (ethylene) 3, 6 © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc.
Big Ideas 2.C.1: Organisms use feedback mechanisms to maintain their internal environments, respond to external changes in environment. 2.D.4: Plants, animals have chemical defenses against infections, interruptions to homeostasis. 2.E.2: Timing, coordination of physiological events are regulated by different mechanisms. 2.E.3: Timing, coordination of behavior are important to natural selection. 3.D.3: Signal transduction pathways link reception with cellular response. 4.A.3: Interactions between external stimuli, regulated gene expression  specialization (cells, tissue, organs). © 2011 Pearson Education, Inc.

Illustrative Examples:
Ripening of fruit (ethylene) Illustrative Examples

Plant defenses against pathogens that trigger infected and adjacent cells to limit spread of infection. Illustrative Examples

Phototropism effects caused by auxin hormone (see Figure 39.5) Illustrative Examples

Phototropism in plants lead to maximum sunlight exposure of leaves  differential survival rates Illustrative Examples

Phytochrome-receptor chain  “de-etiolation” Illustrative Examples

Phytochrome-receptor kinase protein chain  “de-etiolation” Stem elongation slows Leaves expand Roots elongate Production of chlorophyll Illustrative Examples

Beyond the Scope of the AP Exam…
(2.C.2) No specific behavioral/physical mechanisms required (2.E.1) Names of specific stages in embryonic development are required (2.E.2) Memorization of names, molecular structures and specific effects of all plant hormones © 2011 Pearson Education, Inc.

Environmental Influences
Atmosphere: Humidity Air temperature Wind Radiation Plant Regulation: Stomatal Opening Leaf temperature Leaf loss Root development Soil Supply: Soil moisture Soil texture, density Soil temperature Soil depth

Distinction Growth Development
The emergence of specialized, morphologically different body parts. Qualitative in nature Increase in number, size, and/or volume of cells in multicellular organisms Quantitative in nature

Key Points 1) Plants develop via unique combinations of genes, hormones, and the environment. 2) Five plant hormones cause different kinds of growth and development. 3) Plants adjust their growth in response to environmental stimuli. 4) Like other organisms, plants operate according to “biological clocks”. 5) Plant life cycles are influenced by complicated environmental and hormonal cues.

Basic Mechanism of Hormone Action
Reception: Signal (typically hormone) is received by cell Transduction: Often complex series of intermediate steps linking reception and response. Response: how the cell makes sense of input (on, off, or limiting/potentiating activity Three stages of cell signaling (signal-transduction pathway) (a) Local regulators or hormones are released by cells, received, and then acted upon by other cells (b) We can biochemically differentiate the reception, etc. of these chemical signals into three stages: (i) Reception (by a cell) (ii) Transduction (from outside of the cell to inside the cell, etc.) (iii) Response (how the cell responds to having received the signal) (c) See Figure 11.5, Overview of cell signaling (d) Most of this chapter is devoted to discussing the complexity of these processes, with particular emphasis on transduction (e) Note that this signal transduction is simply one of the many highly complex processes one studies when considering the cell biology (and biochemistry) of the cells of multicellular organisms (f) [signal transduction pathway, signal transduction pathways (Google Search)] [index] (6) Reception (a) Reception of a chemical signal literally involves the attachment (or association) of the chemical signal to some aspect of the recipient cell�s plasma membrane (b) The means of reception, typically involving a membrane protein, may be intimately linked to the existence of an intact plasma membrane (c) A membrane is thus a requirement for the occurrence of subsequent signal transduction and response (i.e., cell-to-cell signaling typically requires that recipient cells are intact) (d) [signal reception cell (Google Search)] [index] (7) Transduction (signal transduction) (a) There exist three stages of cell signaling, a beginning, a middle, and an end (b) Signal reception represents the beginning while transduction represents the middle (c) Transduction is the conversion of the reception signal, typically found at the surface of the cell, to a signal that directly facilitates a response (d) Very often signal transduction involves a number of steps that, taken as a whole, can be somewhat complex (perhaps overwhelmingly so) (e) Though not explaining the complexity, nevertheless a basic purpose of the need for signal transduction � linking reception and response � is that the plasma membrane receptor and the molecules involved in formulating a response are not always (rarely?) located in the same region of the cell; thus intracellular signals (often chemical) serve to physically connect reception and response (f) For example, a signal-transduction pathway may involve the following: (i) Reception (at the plasma membrane) � (ii) Transduction (through the cytoplasm) � (iii) Response (in the nucleus, e.g., transcription) (g) [signal transduction (Google Search)] [index] (8) Response (a) The response to cell signaling varies enormously, depending on the signal as well as the receiving cell (b) Suffice it to say that responses typically involve either the turning on of a specific (often enzymatic) activity (including the synthesis of new enzymes) or a reduction in (or turning off of) a specific enzymatic activity (c) In addition, a response can involve the turning on or off of more than one activity (d) �Explanation for the specificity exhibited in cellular responses to signals is the same as the basic explanation for virtually all differences between cells: Different kinds of cells have different collections of proteins. The response of a particular cell to a signal depends on its particular collection of signal receptor proteins, relay proteins, and proteins needed to carry out the response.� (p. 202, Campbell et al., 1999) (e) For the sake of discussion throughout this chapter, consider response to be simply some end point of a signal-transduction pathway

Three stages of cell signaling (signal-transduction pathway)
(a) Local regulators or hormones are released by cells, received, and then acted upon by other cells (b) We can biochemically differentiate the reception, etc. of these chemical signals into three stages: (i) Reception (by a cell) (ii) Transduction (from outside of the cell to inside the cell, etc.) (iii) Response (how the cell responds to having received the signal) (c) See Figure 11.5, Overview of cell signaling (d) Most of this chapter is devoted to discussing the complexity of these processes, with particular emphasis on transduction (e) Note that this signal transduction is simply one of the many highly complex processes one studies when considering the cell biology (and biochemistry) of the cells of multicellular organisms (f) [signal transduction pathway, signal transduction pathways (Google Search)] [index] (6) Reception (a) Reception of a chemical signal literally involves the attachment (or association) of the chemical signal to some aspect of the recipient cell�s plasma membrane (b) The means of reception, typically involving a membrane protein, may be intimately linked to the existence of an intact plasma membrane (c) A membrane is thus a requirement for the occurrence of subsequent signal transduction and response (i.e., cell-to-cell signaling typically requires that recipient cells are intact) (d) [signal reception cell (Google Search)] [index] (7) Transduction (signal transduction) (a) There exist three stages of cell signaling, a beginning, a middle, and an end (b) Signal reception represents the beginning while transduction represents the middle (c) Transduction is the conversion of the reception signal, typically found at the surface of the cell, to a signal that directly facilitates a response (d) Very often signal transduction involves a number of steps that, taken as a whole, can be somewhat complex (perhaps overwhelmingly so) (e) Though not explaining the complexity, nevertheless a basic purpose of the need for signal transduction � linking reception and response � is that the plasma membrane receptor and the molecules involved in formulating a response are not always (rarely?) located in the same region of the cell; thus intracellular signals (often chemical) serve to physically connect reception and response (f) For example, a signal-transduction pathway may involve the following: (i) Reception (at the plasma membrane) � (ii) Transduction (through the cytoplasm) � (iii) Response (in the nucleus, e.g., transcription) (g) [signal transduction (Google Search)] [index] (8) Response (a) The response to cell signaling varies enormously, depending on the signal as well as the receiving cell (b) Suffice it to say that responses typically involve either the turning on of a specific (often enzymatic) activity (including the synthesis of new enzymes) or a reduction in (or turning off of) a specific enzymatic activity (c) In addition, a response can involve the turning on or off of more than one activity (d) �Explanation for the specificity exhibited in cellular responses to signals is the same as the basic explanation for virtually all differences between cells: Different kinds of cells have different collections of proteins. The response of a particular cell to a signal depends on its particular collection of signal receptor proteins, relay proteins, and proteins needed to carry out the response.� (p. 202, Campbell et al., 1999) (e) For the sake of discussion throughout this chapter, consider response to be simply some end point of a signal-transduction pathway

Action of Hormones In general hormones control plant development by:
Division of cells Elongation Differentiation of cells Physiological response to environmental for short term periods (stomatal opening)

Action of Hormones They do this by regulating:
gene expression (transcriptional control) activity of enzymes (post-transcriptional control) changing membrane properties e.g. sterols: increasing fluidity

Growth in Animals Animals grow throughout the whole organism
many regions & tissues at different rates

Growth in Plants Specific regions of growth: meristems
stem cells: perpetually embryonic tissue regenerate new cells apical shoot meristem growth in length primary growth apical root meristem lateral meristem growth in girth secondary growth

Plant Hormone Location Functions
Gibberellins Apical meristems of buds, roots, leaves, embryos Promotes stem elongation; ends dormancy of seeds, buds Auxins Bud, leaf apical meristems & embryos Promote cell elongation; role in photo/gravitropism Cytokinins Made in roots, travels elsewhere Promote cell division, leaf expansion; retards leaf aging Abscisic Acid Leaves, stems, & unripened fruit Promotes stomatal closure, bud and seed dormancy Ethylene Notable amounts in seeds, fruits, stems, leaves, and roots Promotes ripening of fruit, abscission of leaves, flowers, fruits, roots

G G G G

Gibberellins Family of hormones Effects
over 100 different gibberellins identified Effects stem elongation fruit growth seed germination plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

Gibberellins Apical meristems of buds, roots, leaves, embryos Promotes stem elongation; ends dormancy of seeds, buds Auxins Bud, leaf apical meristems & embryos Promote cell elongation; role in photo/gravitropism Cytokinins Made in roots, travels elsewhere Promote cell division, leaf expansion; retards leaf aging Abscisic Acid Leaves, stems, & unripened fruit Promotes stomatal closure, bud and seed dormancy Ethylene Notable amounts in seeds, fruits, stems, leaves, and roots Promotes ripening of fruit, abscission of leaves, flowers, fruits, roots

G A A G G A G

Auxin Effects controls cell division & differentiation phototropism
growth towards light asymmetrical distribution of auxin cells on darker side elongate faster than cells on brighter side apical dominance

Gibberellins Apical meristems of buds, roots, leaves, embryos Ptomotes stem elongation; ends dormancy of seeds, buds Auxins Bud, leaf apical meristems & embryos Promote cell elongation; role in photo/gravitropism Cytokinins Made in roots, travels elsewhere Promote cell division, leaf expansion; retards leaf aging Abscisic Acid Leaves, stems, & unripened fruit Promotes stomatal closure, bud and seed dormancy Ethylene Notable amounts in seeds, fruits, stems, leaves, and roots Promotes ripening of fruit, abscission of leaves, flowers, fruits, roots

G A A G G A G C

Cytokinins Effects Stimulates cell division
Used to prolong shelf life of cut flowers, other fruits & veggies Most abundant in root, shoot meristems

G A AA A G AA G A G C AA

Abscisic acid Effects slows growth seed dormancy
high concentrations of abscisic acid germination only after it is inactivated or leeched out survival value: seed will germinate only under optimal conditions light, temperature, moisture

G A AA E A E G AA G A E G C AA E

Big Ideas 2.E.1) Timing and coordination of specific events are necessary for the normal development of an organism, and these events are regulated by a variety of mechanisms. Illustrative Examples Illustrative Examples: Flower development © 2011 Pearson Education, Inc.

One bad apple spoils the whole bunch…
Ethylene Hormone gas released by plant cells Effects fruit ripening leaf drop like in Autumn apoptosis One bad apple spoils the whole bunch…

Fruit ripening Adaptation Mechanism
hard, tart fruit protects developing seed from herbivores ripe, sweet, soft fruit attracts animals to disperse seed Mechanism triggers ripening process breakdown of cell wall softening conversion of starch to sugar sweetening positive feedback system ethylene triggers ripening ripening stimulates more ethylene production

Mix & Match Review: Ch Phytochromes Circadian rhythms Tropisms (3 kinds) 1, 4, 7 Environmental factors affecting plants (list, describe at least five) 2, 5, 8 Plant defenses (list, describe at least five) 3, 6 © 2011 Pearson Education, Inc.

Hormones and Plant Tropisms:
Plant tropism: when a root or a shoot turns toward or away from a stimulus, caused by hormone mediated shifts in the rates at which different cells grow and elongate. Plant tropisms include: Gravitropism (growth away from/toward gravity) Phototropism (growth toward light) Thigmotropism (growth away from mechanical pressure)

Adjustment in the Rate and Direction of Growth
Gravitropism Response to gravity Root curves down (+ gravitropism) Shoot curves up (- gravitropism)

Gravitropism Response to gravity Root curves down (+ gravitropism) Shoot curves up (- gravitropism) Hormone responsible: AUXIN Auxin causes cell elongation Auxin is inhibitory in high concentrations in root tissue

Gravitropism Response to gravity Root curves down (+ gravitropism) Shoot curves up (- gravitropism) Hormone responsible: AUXIN Auxin causes cell elongation Auxin is inhibitory in high concentrations in root tissue Statoliths are involved in root response They are clusters of unbound starch grains in plastids They settle to the bottoms of root cells and redistribute auxin

Gravitropism: Shoot Mechanism
Effect as soon as 30 min CELL High auxin = high elongation

Gravitropism Root Mechanism:
HOW??? Statoliths settle to bottom of root cells. Auxins are pushed out of root tip. High [AUX] = elongation inhibited. Curves down. Cells elongate Cells here inhibited from elongation

Sideways orientation Normal orientation statoliths
position within 2 hours Fig. 32.9, p. 550 Effect as soon as 5 min position at 30 minutes

Phototropism Response to light Whenever stems or leaves adjust the rate and direction of their growth in response to light Hormone responsible: AUXIN Auxin causes cell elongation Mechanism: Auxin moves from the tip of the shoot into cells less exposed to light. The cells on the side away from the light elongate and cause the stem to bend toward the light.

Phototropism in Coleoptile

Thigmotropism: SLOW RESPONSE Response to contact with solid objects Whenever stems or leaves adjust the rate and direction of their growth in response to contact with another object Hormones responsible: AUXIN and ETHYLENE Auxin causes cell elongation Mechanism Auxin moves into cells away from the contact point. The cells on the side away from the contact elongate and cause the tendril or vine to coil.

Fig , p. 551 Elongation on this side Tree

Thigmotropism: QUICK RESPONSE Response to contact with solid objects Whenever stems or leaves adjust the rate and direction of their growth in response to contact with another object There is an example of thigmotropism that is not hormone-mediated! Mechanism Changes in turgor pressure cause movement.

Sensitive Mimosa After Contact Before Contact

Apoptosis in plants Many events in plants involve apoptosis
What is the evolutionary advantage of loss of leaves in autumn? Many events in plants involve apoptosis response to hormones ethylene auxin death of annual plant after flowering senescence differentiation of xylem vessels loss of cytoplasm shedding of autumn leaves The loss of leaves each autumn is an adaptation that keeps deciduous trees from desiccating during winter when the roots cannot absorb water from the frozen ground. Before leaves abscise, many essential elements are salvaged from the dying leaves and are stored in stem parenchyma cells. These nutrients are recycled back to developing leaves the following spring. Fall color is a combination of new red pigments made during autumn and yellow and orange carotenoids that were already present in the leaf but are rendered visible by the breakdown of the dark green chlorophyll in autumn. Photo: Abscission of a maple leaf. Abscission is controlled by a change in the balance of ethylene and auxin. The abscission layer can be seen here as a vertical band at the base of the petiole. After the leaf falls, a protective layer of cork becomes the leaf scar that helps prevent pathogens from invading the plant (LM).

Illustrative Examples: Biology of Pollination
Big Ideas 2.E.3) Timing and coordination of behavior are regulated by various mechanisms and are important in natural selction. Illustrative Examples Illustrative Examples: Biology of Pollination © 2011 Pearson Education, Inc.

Illustrative Examples: Circadian rhythms/24-hour clock
Big Ideas 2.E.2) Timing and coordination of physiological events are regulated by multiple mechanisms. Illustrative Examples Illustrative Examples: Circadian rhythms/24-hour clock © 2011 Pearson Education, Inc.

Mechanism for Timing & Controlling Events
Biological Clock (B.C.): internal timing mechanism that sets the time for recurring changes in biochemical events daily and seasonal adjustments in patterns of growth, development and reproduction Circadian rhythm (subset of B.C.s): A biological activity that recurs in cycles of about 24 hours (21-27 is typical); act independent of stimuli These rhythms are controlled by biological clocks Examples: sleep-wake cycles, active-inactive periods, rhythmic leaf shifts

1 A.M. 6 A.M. NOON 3 P.M. 10 P.M. MIDNIGHT Refer to Fig

Photoperiodism is regulated by phytochrome.
Photoperiodism: Effect of biological clock and phytochrome working together Photoperiodism: Any biological response to the change in the relative length of daylight and darkness in the cycle of 24 hours Example: photoperiod control of flowering Photoperiodism is regulated by phytochrome. Blue-green pigment i.e. a photoreceptor There is a protein covalently bonded to the light absorbing part of the molecule called a chromophore

Phytochrome Molecule:

Photoperiodism: Chromophore: changes from one isomeric form to another and this activates or inactivates the phytochrome molecule. Common at dawn Common at dusk Page 552

Photoperiodism: Phytochrome is located in the plasma membrane.
When in active form, Pfr can for example trigger germination or flowering. Let’s look at the example of photoperiodism and flowering control. SDP, LDP, DNP

Flowering - A Case of Photoperiodism
Short-day plants: flower in late summer, early fall Ex.: strawberry, poinsettias Long-day plants: flower in the spring Ex.: petunia, iris, potato Day-neutral plants: flower when mature Ex.: tomatoes, rice, rose

Flowering - A Case of Photoperiodism
Short-day plants: flower when day length is less than the critical value Long-day plants:flower when the day length is greater than the critical value Day-neutral plants: flower when mature

Photoperiodism and Flowering:
Advantages: Day/night length less variable than temperature and therefore a better judge of seasonality Increases reproductive efficiency Coordination and balance with pollinators

Chapter 32: Plant Response to Stimuli Photoperiodism and Flowering: Now we will apply what we have learned about phytochrome and photoperiodism to make predictions about whether or not plants will flower.

What would flower: SDP? LDP? DNP?
Photoperiodism and Flowering: A 24 12 24 hours Critical night length Critical day length What would flower: SDP? LDP? DNP?

B C D E F 24 FR R 24 hours 12

Concept 39.3: Responses to light are critical for plant success
Light cues many key events in plant growth and development Effects of light on plant morphology are called photomorphogenesis © 2011 Pearson Education, Inc.

Plants detect not only presence of light but also its direction, intensity, and wavelength (color) A graph called an action spectrum depicts relative response of a process to different wavelengths Action spectra are useful in studying any process that depends on light © 2011 Pearson Education, Inc.

Fig. 39.16 1.0 436 nm 0.8 0.6 Phototropic effectiveness 0.4 0.2 400
Figure 39.16 1.0 436 nm Fig 0.8 0.6 Phototropic effectiveness 0.4 0.2 400 450 500 550 600 650 700 Wavelength (nm) (a) Phototropism action spectrum Light Figure Action spectrum for blue-light-stimulated phototropism in maize coleoptiles. Time  0 min Time  90 min (b) Coleoptiles before and after light exposures

Phototropic effectiveness (a) Phototropism action spectrum
Figure 39.16a 1.0 436 nm 0.8 0.6 Phototropic effectiveness 0.4 0.2 Figure Action spectrum for blue-light-stimulated phototropism in maize coleoptiles. 400 450 500 550 600 650 700 Wavelength (nm) (a) Phototropism action spectrum

(b) Coleoptiles before and after light exposures
Figure 39.16b Light Time  0 min Time  90 min Figure Action spectrum for blue-light-stimulated phototropism in maize coleoptiles. (b) Coleoptiles before and after light exposures

Blue-Light Photoreceptors
Various blue-light photoreceptors control hypocotyl elongation, stomatal opening, and phototropism © 2011 Pearson Education, Inc.

Phytochromes as Photoreceptors
Phytochromes are pigments that regulate many of a plant’s responses to light throughout its life These responses include: seed germination shade avoidance © 2011 Pearson Education, Inc.

Phytochromes and Seed Germination
Many seeds remain dormant until light conditions change In the 1930s, scientists at the U.S. Department of Agriculture determined the action spectrum for light-induced germination of lettuce seeds © 2011 Pearson Education, Inc.

Fig. 39.17 RESULTS Red Dark Red Far-red Dark Dark (control) Red
Figure 39.17 Fig RESULTS Red Dark Red Far-red Dark Dark (control) Figure Inquiry: How does the order of red and far-red illumination affect seed germination? Red Far-red Red Dark Red Far-red Red Far-red

Dark (control) Figure 39.17a
Figure Inquiry: How does the order of red and far-red illumination affect seed germination?

Figure 39.17b Red Dark Figure Inquiry: How does the order of red and far-red illumination affect seed germination?

Red Far-red Dark Figure 39.17c

Red Far-red Red Dark Figure 39.17d

Red Far-red Red Far-red
Figure 39.17e Red Far-red Red Far-red Figure Inquiry: How does the order of red and far-red illumination affect seed germination?

Red light increased (+) germination Far-red light inhibited (-) germination The photoreceptor responsible for the opposing effects of red and far-red light is a phytochrome © 2011 Pearson Education, Inc.

Two identical subunits Photoreceptor activity
Figure 39.18 Two identical subunits Chromophore Photoreceptor activity Figure Structure of a phytochrome. Kinase activity

Red light Pr Pfr Far-red light
Figure 39.UN01 Red light Pr Pfr Figure 39.UN01 In-text figure, p. 837 Far-red light

Phytochromes exist in two photoreversible states, with conversion of Pr to Pfr triggering many developmental responses Red light triggers the conversion of Pr to Pfr Far-red light triggers the conversion of Pfr to Pr The conversion to Pfr is faster than the conversion to Pr Sunlight increases the ratio of Pfr to Pr, and triggers germination © 2011 Pearson Education, Inc.

Responses: seed germination, control of flowering, etc.
Figure 39.19 Pr Pfr Red light Responses: seed germination, control of flowering, etc. Synthesis Far-red light Slow conversion in darkness (some plants) Enzymatic destruction Figure Phytochrome: a molecular switching mechanism.

Phytochromes and Shade Avoidance
The phytochrome system also provides the plant with information about the quality of light Leaves in the canopy absorb red light Shaded plants receive more far-red than red light In the “shade avoidance” response, the phytochrome ratio shifts in favor of Pr when a tree is shaded © 2011 Pearson Education, Inc.

Biological Clocks and Circadian Rhythms
Many plant processes oscillate during the day Many legumes lower their leaves in the evening and raise them in the morning, even when kept under constant light or dark conditions © 2011 Pearson Education, Inc.

Figure 39.20 Figure Sleep movements of a bean plant (Phaseolus vulgaris). Noon Midnight

Figure 39.20a Figure Sleep movements of a bean plant (Phaseolus vulgaris). Noon

Figure 39.20b Figure Sleep movements of a bean plant (Phaseolus vulgaris). Midnight

Circadian rhythms are cycles that are about 24 hours long and are governed by an internal “clock” Circadian rhythms can be entrained to exactly 24 hours by the day/night cycle The clock may depend on synthesis of a protein regulated through feedback control and may be common to all eukaryotes © 2011 Pearson Education, Inc.

The Effect of Light on the Biological Clock
Phytochrome conversion marks sunrise and sunset, providing the biological clock with environmental cues © 2011 Pearson Education, Inc.

Photoperiodism and Responses to Seasons
Photoperiod, the relative lengths of night and day, is the environmental stimulus plants use most often to detect the time of year Photoperiodism is a physiological response to photoperiod © 2011 Pearson Education, Inc.

Photoperiodism and Control of Flowering
Some processes, including flowering in many species, require a certain photoperiod Plants that flower when a light period is shorter than a critical length are called short-day plants Plants that flower when a light period is longer than a certain number of hours are called long-day plants Flowering in day-neutral plants is controlled by plant maturity, not photoperiod © 2011 Pearson Education, Inc.

Short-day plants are governed by whether the critical night length sets a minimum number of hours of darkness Long-day plants are governed by whether the critical night length sets a maximum number of hours of darkness © 2011 Pearson Education, Inc.

Short day (long-night) plant Long-day (short-night) plant
Figure 39.21 24 hours (a) Short day (long-night) plant Light Flash of light Darkness Critical dark period (b) Long-day (short-night) plant Figure Photoperiodic control of flowering. Flash of light

Red light can interrupt the nighttime portion of the photoperiod A flash of red light followed by a flash of far-red light does not disrupt night length Action spectra and photoreversibility experiments show that phytochrome is the pigment that receives red light © 2011 Pearson Education, Inc.

Short-day (long-night) plant Long-day (short-night) plant
Figure 39.22 24 hours R R FR Figure Reversible effects of red and far-red light on photoperiodic response. R FR R R FR R FR Short-day (long-night) plant Long-day (short-night) plant Critical dark period

Some plants flower after only a single exposure to the required photoperiod Other plants need several successive days of the required photoperiod Still others need an environmental stimulus in addition to the required photoperiod For example, vernalization is a pretreatment with cold to induce flowering © 2011 Pearson Education, Inc.

A Flowering Hormone? Photoperiod is detected by leaves, which cue buds to develop as flowers The flowering signal is called florigen Florigen may be a macromolecule governed by the FLOWERING LOCUS T (FT) gene © 2011 Pearson Education, Inc.

Long-day plant grafted to short-day plant
Figure 39.23 24 hours 24 hours 24 hours Graft Figure Experimental evidence for a flowering hormone. Short-day plant Long-day plant grafted to short-day plant Long-day plant

Big Ideas 2.D.4) Plants and animals have a variety of chemical defenses against infections that affect dynamic homeostasis. Illustrative Examples Illustrative Examples: Plant defenses against pathogens (see Fig ) © 2011 Pearson Education, Inc.

Plant Growth & Development

Similar presentations

Presentation on theme: "Plant Growth & Development"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Plant Growth & Development

Similar presentations

Presentation on theme: "Plant Growth & Development"— Presentation transcript:

Similar presentations

About project

Feedback