Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 39 Plant Responses to Internal and External Signals

Fig (a) Before exposure to light (b) After a week’s exposure to natural daylight Concept 39.1: Signal transduction pathways link signal reception to response

Fig CYTOPLASM Reception Plasma membrane Cell wall Phytochrome activated by light Light Transduction Second messenger produced cGMP NUCLEUS 1 2 Specific protein kinase 1 activated

Fig CYTOPLASM Reception Plasma membrane Cell wall Phytochrome activated by light Light Transduction Second messenger produced cGMP Specific protein kinase 1 activated NUCLEUS 1 2 Specific protein kinase 2 activated Ca 2+ channel opened Ca 2+

Fig CYTOPLASM Reception Plasma membrane Cell wall Phytochrome activated by light Light Transduction Second messenger produced cGMP Specific protein kinase 1 activated NUCLEUS 1 2 Specific protein kinase 2 activated Ca 2+ channel opened Ca 2+ Response 3 Transcription factor 1 Transcription factor 2 NUCLEUS Transcription Translation De-etiolation (greening) response proteins P P

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 39.2: Plant hormones help coordinate growth, development, and responses to stimuli _______________are chemical signals that coordinate different parts of an organism Any response resulting in curvature of organs toward or away from a stimulus is called a _______________ Tropisms are often caused by hormones

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings A Survey of Plant Hormones In general, hormones control plant growth and development by affecting the division, elongation, and differentiation of cells Plant hormones are produced in very low concentration, but a minute amount can greatly affect growth and development of a plant organ

Table 39-1

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Auxin Stimulates stem elongation and growth by softening cell wall ___________________ – Growth towards light – Asymmetrical distribution of auxin (cells on darker side elongate faster than cells on brighter side) Enhances ____________________, so plants grow upwards rather than laterally

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cytokinins Stimulate _______________(cell division) Work together with ________ to control cell division and differentiation Produced in ______ and travel upwards Delay _____________ (aging of plant organs) by inhibiting protein breakdown, stimulating RNA and protein synthesis, and mobilizing nutrients from surrounding tissues

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gibberellins Family of hormones – over 100 different gibberellins identified Effects – ____________________ plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Brassinosteroids Brassinosteroids are chemically similar to the sex hormones of animals They induce cell elongation and division in stem segments

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Abscisic Acid Abscisic acid (ABA) slows growth Two of the many effects of ABA: ___________________

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ethylene Ethylene is a ________ Plants produce ethylene in response to stresses such as drought, flooding, mechanical pressure, injury, and infection Effects include: – ____________________

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fruit ripening Adaptation –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

Fig mm Protective layer Stem Abscission layer Petiole

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 39.3: Responses to light are critical for plant success Light cues many key events in plant growth and development There are two major classes of light receptors: ____________________ and ____________________

Fig. 39-UN1 Red light Far-red light PrPr P fr

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Biological Clocks and Circadian Rhythms Many plant processes oscillate during the day _____________________ are cycles that are about 24 hours long and are governed by an internal “clock”

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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 ________________________ Plants that flower when a light period is longer than a certain number of hours are called ________________________ Flowering in day-neutral plants is controlled by plant maturity, not photoperiod

Fig hours Light Critical dark period Flash of light Darkness (a) Short-day (long-night) plant Flash of light (b) Long-day (short-night) plant

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings You should now be able to: 1.Compare the growth of a plant in darkness (etiolation) to the characteristics of greening (de-etiolation) 2.List six classes of plant hormones and describe their major functions 3.Describe the phenomenon of phytochrome photoreversibility and explain its role in light- induced germination of lettuce seeds 4.Explain how light entrains biological clocks

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 5.Distinguish between short-day, long-day, and day-neutral plants; explain why the names are misleading 6.Describe how plants tell up from down 7.Distinguish between thigmotropism and thigmomorphogenesis 8.Describe the challenges posed by, and the responses of plants to, drought, flooding, salt stress, heat stress, and cold stress

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 9.Describe how the hypersensitive response helps a plant limit damage from a pathogen attack