After studying this chapter you will be able to understand: Stimuli and a stationary life; signal transduction pathways link signal reception to response; plant hormones help coordinate growth, development, and responses to stimuli; responses to light are critical for plant success; plants respond to a wide variety of stimuli other than light; plants defend themselves against herbivores and pathogens. | Chapter 39 Plant Responses to Internal and External Signals Overview: Stimuli and a Stationary Life Plants, being rooted to the ground Must respond to whatever environmental change comes their way For example, the bending of a grass seedling toward light Begins with the plant sensing the direction, quantity, and color of the light Figure Concept : Signal transduction pathways link signal reception to response Plants have cellular receptors That they use to detect important changes in their environment For a stimulus to elicit a response Certain cells must have an appropriate receptor A potato left growing in darkness Will produce shoots that do not appear healthy, and will lack elongated roots These are morphological adaptations for growing in darkness Collectively referred to as etiolation Figure (a) Before exposure to light. A dark-grown potato has tall, spindly stems and nonexpanded leaves—morphological adaptations that enable the shoots to penetrate the soil. The roots are short, but there is little need for water absorption because little water is lost by the shoots. After the potato is exposed to light The plant undergoes profound changes called de-etiolation, in which shoots and roots grow normally Figure (b) After a week’s exposure to natural daylight. The potato plant begins to resemble a typical plant with broad green leaves, short sturdy stems, and long roots. This transformation begins with the reception of light by a specific pigment, phytochrome. The potato’s response to light Is an example of cell-signal processing Figure CELL WALL CYTOPLASM 1 Reception 2 Transduction 3 Response Receptor Relay molecules Activation of cellular responses Hormone or environmental stimulus Plasma membrane Reception Internal and external signals are detected by receptors Proteins that change in response to specific stimuli Transduction Second messengers Transfer and amplify signals from receptors to proteins that cause specific responses . | Chapter 39 Plant Responses to Internal and External Signals Overview: Stimuli and a Stationary Life Plants, being rooted to the ground Must respond to whatever environmental change comes their way For example, the bending of a grass seedling toward light Begins with the plant sensing the direction, quantity, and color of the light Figure Concept : Signal transduction pathways link signal reception to response Plants have cellular receptors That they use to detect important changes in their environment For a stimulus to elicit a response Certain cells must have an appropriate receptor A potato left growing in darkness Will produce shoots that do not appear healthy, and will lack elongated roots These are morphological adaptations for growing in darkness Collectively referred to as etiolation Figure (a) Before exposure to light. A dark-grown potato has tall, spindly stems and nonexpanded leaves—morphological adaptations that enable the shoots to penetrate the soil. .
