30.6 Plant Sensory Systems and Responses
4 min read•june 14, 2024
Plants are masters of adaptation, responding to light and gravity in fascinating ways. Red and blue light trigger specific growth responses, while ensures proper orientation. These mechanisms allow plants to optimize their growth and survival in diverse environments.
Plant hormones orchestrate complex responses to stimuli, regulating everything from growth to stress tolerance. Meanwhile, thigmo responses and defense mechanisms protect plants from physical threats and predators. These intricate systems showcase plants' remarkable ability to sense and react to their surroundings.
Plant Responses to Light and Gravity
Red and blue light in plant growth
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- Red light
- Absorbed by photoreceptors triggers physiological responses
- Stimulates seed germination breaking dormancy and promoting early growth
- Promotes stem elongation and leaf expansion increasing plant height and leaf area
- Enhances flowering in some long-day plants (spinach) by regulating
- Blue light
- Absorbed by and photoreceptors initiates specific responses
- Stimulates (growth towards light) optimizing light capture for photosynthesis
- Regulates stomatal opening for gas exchange facilitating CO2 uptake and transpiration
- Influences chloroplast movement within cells maximizing light absorption efficiency
- Inhibits stem elongation, promoting compact growth for sturdy plant structure
Gravitropism for plant orientation
- Gravitropism is a plant's growth response to gravity enabling proper orientation
- Roots exhibit
- Grow downward, towards the center of gravity following the gravitational pull
- Allows roots to anchor the plant and absorb water and nutrients from soil
- Shoots exhibit
- Grow upward, away from the center of gravity opposing the gravitational force
- Enables leaves to receive sunlight for photosynthesis optimizing energy capture
- (dense starch granules) in root cap cells and endodermal cells
- Settle to the bottom of cells in response to gravity due to their high density
- Trigger redistribution of , leading to differential growth on opposite sides
Plant Hormones and Responses to Stimuli
Hormones in plant development
- (, )
- Stimulate cell elongation and division promoting growth and development
- Promote apical dominance and inhibit lateral bud growth shaping plant architecture
- Involved in phototropism and gravitropism mediating growth responses to stimuli
- Cytokinins
- Promote cell division and differentiation driving organ formation and growth
- Delay leaf senescence maintaining photosynthetic capacity and nutrient remobilization
- Interact with auxins to regulate shoot and root growth balancing plant development
-
- Stimulate stem elongation and leaf expansion increasing plant height and leaf area
- Promote seed germination and fruit development enhancing reproductive success
- ()
- Regulates stomatal closure during water stress conserving water and preventing dehydration
- Induces seed and bud dormancy ensuring survival during unfavorable conditions
- Inhibits growth during unfavorable conditions allocating resources to stress tolerance
-
- Promotes fruit ripening and leaf coordinating senescence and dispersal
- Induces senescence and stress responses adapting to environmental changes
Thigmo responses of plants
-
- Directional growth response to touch or contact guiding plant growth and support
- Tendrils of climbing plants (peas) coiling around support structures for vertical growth
- (an example of )
- Non-directional, reversible movement in response to touch facilitating prey capture or defense
- Closing of Venus flytrap leaves when triggered by prey to trap and digest insects
-
- Touch-induced changes in plant growth and development adapting to mechanical stress
- Wind-induced stem thickening and reduced elongation increasing mechanical strength
Plant defenses against predators
- Physical defenses
- Thorns, spines, and prickles deter herbivores (roses) reducing tissue damage
- Thick cuticles and bark protect against damage limiting pathogen entry and water loss
- Chemical defenses
- Secondary metabolites (alkaloids, terpenes) deter or poison herbivores (nicotine in tobacco)
- Volatile compounds attract predators of herbivores (parasitic wasps) for indirect defense
- Wound responses
- Compartmentalization of damaged areas to prevent spread of infection localizing damage
- Production of defensive compounds (lignin, suberin) to seal wounds and reinforce cell walls
- Activation of systemic acquired resistance (SAR) to protect undamaged tissues enhancing overall defense
Plant Sensory Systems and Environmental Responses
Circadian rhythm and plant behavior
- Internal biological clock regulating physiological processes and gene expression
- Influences timing of stomatal opening, photosynthetic activity, and flowering
- Helps plants anticipate and prepare for daily environmental changes
Signal transduction in plant responses
- Converts environmental stimuli into cellular responses through molecular pathways
- Involves receptors, secondary messengers, and transcription factors
- Enables plants to respond to various environmental cues and stresses
Plant stress responses
- Physiological and biochemical changes in response to adverse environmental conditions
- Includes responses to drought, salinity, extreme temperatures, and pathogen attacks
- Involves activation of stress-responsive genes and production of protective compounds
Key Terms to Review (42)
ABA: ABA, or abscisic acid, is a plant hormone that plays a crucial role in regulating various physiological processes, especially in response to environmental stresses. It is primarily involved in promoting seed dormancy, stomatal closure during water scarcity, and influencing plant responses to stress factors like drought and salinity. This hormone acts as a key player in the plant sensory systems, helping plants adapt to their changing environment.
Abscisic acid: Abscisic acid is a plant hormone that plays a crucial role in regulating various physiological processes, particularly in response to stress conditions such as drought and salinity. This hormone helps plants conserve water by promoting stomatal closure, thus reducing transpiration and aiding in the transport of water and solutes during challenging environmental conditions.
Abscission: Abscission is the process by which plants shed leaves, flowers, or fruits. It is a crucial mechanism for plant survival and adaptation, often triggered by environmental cues or hormonal changes.
Amyloplasts: Amyloplasts are specialized organelles in plant cells responsible for the synthesis and storage of starch. They are a type of plastid that plays a crucial role in converting glucose into starch for long-term energy storage.
Auxin: Auxin is a plant hormone that plays a crucial role in regulating growth and responses to environmental stimuli. It influences various physiological processes, including cell elongation, root formation, and tropisms, allowing plants to adapt to their surroundings and optimize resource use. By promoting growth on the side of the plant that is away from light, auxin helps direct growth towards favorable conditions.
Auxins: Auxins are a class of plant hormones that play a crucial role in the regulation of plant growth and development. They are primarily responsible for cell elongation, root formation, and responses to light and gravity.
Chromophore: A chromophore is a part of a molecule responsible for its color. It absorbs certain wavelengths of light and reflects others, giving the molecule its visible color.
Circadian Rhythm: Circadian rhythm refers to the physical, mental, and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism's environment. This internal clock influences various physiological processes, including sleep-wake cycles, hormone release, and metabolism, playing a crucial role in how organisms adapt to their environment. Circadian rhythms are essential for maintaining homeostasis and optimizing function in plants and animals alike.
Cryptochrome: Cryptochrome is a blue-light photoreceptor protein found in plants that plays a vital role in regulating various physiological processes, including seed germination, flowering time, and the circadian rhythm. It detects blue light and enables plants to respond to changes in light conditions, which is essential for optimizing growth and development.
Cryptochromes: Cryptochromes are a class of flavoproteins that are sensitive to blue light and play a crucial role in the circadian rhythms and photomorphogenesis of plants. They help plants adapt to their light environment, influencing growth and development processes.
Cytokinin: Cytokinins are a class of plant hormones that play a critical role in cell division, growth, and differentiation. They are essential for various plant processes, including the regulation of shoot and root development, and the promotion of cell proliferation. Cytokinins are involved in plant responses to environmental stimuli, helping plants adapt to changing conditions by influencing growth patterns and physiological responses.
Ethylene: Ethylene is a gaseous plant hormone that regulates various aspects of growth, development, and responses to stress. It is particularly known for its role in fruit ripening and leaf abscission.
Ethylene: Ethylene is a plant hormone that plays a crucial role in regulating various aspects of plant growth, development, and responses to environmental stimuli. This gaseous hormone influences processes like fruit ripening, leaf abscission, and responses to stress, making it a key player in plant sensory systems and how plants adapt to their surroundings.
Gibberellin: Gibberellin is a plant hormone that plays a crucial role in regulating growth and development processes, such as seed germination, stem elongation, and flowering. This hormone helps plants respond to environmental cues, promoting elongation in response to light and gravity, thus ensuring proper development and adaptation to their surroundings.
Gibberellins: Gibberellins are a group of plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, and flowering. They play a crucial role in breaking seed dormancy and promoting growth under favorable conditions.
Gravitropism: Gravitropism is the directional growth response of a plant to gravity, where roots grow downward (positive gravitropism) and stems grow upward (negative gravitropism). This growth behavior allows plants to orient themselves properly in their environment, optimizing their ability to access water, nutrients, and sunlight.
IAA: IAA, or indole-3-acetic acid, is a key plant hormone belonging to the auxin class that plays a crucial role in regulating various growth and developmental processes in plants. It influences cell elongation, root formation, and responses to light and gravity, making it essential for plant adaptation and survival. By facilitating these processes, IAA helps plants optimize their growth in response to environmental stimuli.
Indole-3-acetic acid: Indole-3-acetic acid (IAA) is a naturally occurring plant hormone that plays a crucial role in regulating various aspects of plant growth and development, particularly in cell elongation, root formation, and response to light and gravity. It is classified as an auxin, which are hormones involved in coordinating many growth processes in plants, affecting how they respond to their environment.
Jasmonates: Jasmonates are plant hormones that regulate various aspects of growth, development, and defense responses. They play a crucial role in the plant's ability to respond to environmental stress and herbivory.
Nastic movement: Nastic movement refers to the non-directional, rapid movements of plant parts in response to stimuli, such as light or touch. Unlike tropic movements, which are directional and depend on the stimulus's location, nastic movements occur independently of the direction of the stimulus, allowing plants to adapt quickly to environmental changes.
Negative gravitropism: Negative gravitropism is the growth of plant organs in the opposite direction of gravitational pull. It is commonly observed in stems and leaves growing upward away from the earth.
Oligosaccharins: Oligosaccharins are small carbohydrate fragments derived from the degradation of cell wall polysaccharides. They play crucial roles in plant defense and developmental processes by acting as signaling molecules.
Photoperiodism: Photoperiodism is the physiological reaction of organisms to the length of day or night. In plants, it influences processes such as flowering, seed germination, and dormancy.
Photoperiodism: Photoperiodism is the physiological reaction of organisms to the length of day or night, particularly in plants. This response influences various biological processes such as flowering, germination, and dormancy, allowing plants to synchronize their life cycles with seasonal changes in light. By detecting changes in photoperiod, plants can optimize their growth and reproduction based on environmental conditions.
Phototropin: Phototropin is a blue light receptor in plants that plays a crucial role in regulating phototropic responses, allowing plants to grow towards light sources. This protein contains flavin chromophores that absorb blue light, triggering signal transduction pathways that lead to plant growth adjustments. By facilitating the bending of stems and leaves toward light, phototropins are vital for optimizing photosynthesis and overall plant health.
Phototropins: Phototropins are a type of blue light receptor proteins found in plants. They play a crucial role in mediating various light-dependent processes such as phototropism, chloroplast movement, and stomatal opening.
Phototropism: Phototropism is the growth response of a plant to light, where the plant bends or grows toward the light source. This phenomenon is vital for optimizing photosynthesis, as plants need light to produce energy. Phototropism occurs due to differential growth rates on the sides of the plant that are exposed to light versus those that are in shade, leading to directional growth that maximizes light capture.
Phytochrome: Phytochrome is a photoreceptor protein found in plants that plays a critical role in sensing light and regulating various physiological processes, including seed germination, stem elongation, and flowering. It exists in two interconvertible forms: Pr, which absorbs red light, and Pfr, which absorbs far-red light, allowing plants to respond to changes in light conditions throughout their lifecycle.
Phytochromes: Phytochromes are a class of photoreceptor proteins in plants that detect light and mediate various physiological responses to it. They play crucial roles in regulating processes such as seed germination, stem elongation, and flowering time.
Plant Sensory Systems: Plant sensory systems refer to the mechanisms by which plants perceive and respond to environmental stimuli. These systems are crucial for survival as they allow plants to detect changes in light, gravity, temperature, water availability, and the presence of pathogens, enabling adaptive responses that enhance growth and reproduction.
Plant stress response: Plant stress response refers to the physiological and biochemical changes that occur in plants when they encounter various environmental stressors, such as drought, extreme temperatures, salinity, or pathogen attack. These responses enable plants to adapt to challenging conditions, ensuring their survival and maintaining growth. Through complex signaling pathways and adaptive mechanisms, plants can sense stressors and initiate appropriate responses, such as activating stress-related genes and producing protective compounds.
Positive gravitropism: Positive gravitropism is the growth of plant roots downward, towards the direction of gravitational pull. It ensures that roots anchor the plant and access water and nutrients from the soil.
Signal transduction: Signal transduction is the process by which cells convert external signals into functional responses, allowing them to communicate and adapt to their environment. This involves a series of molecular events, including the reception of signaling molecules, propagation of the signal through cellular pathways, and eventual cellular responses that influence activities such as growth, metabolism, and immune reactions.
Statoliths: Statoliths are specialized organelles in plant cells that assist in gravity perception. They are dense, starch-filled plastids found in root cap cells and other tissues involved in gravitropism.
Statoliths: Statoliths are specialized organelles found in certain plant cells that play a crucial role in gravity sensing and response. They are dense, starch-filled structures that help plants determine their orientation in relation to gravity, allowing them to grow roots downward and stems upward. This mechanism is vital for proper growth and development as it enables plants to adjust their growth direction based on gravitational forces.
Strigolactones: Strigolactones are a class of plant hormones that regulate various aspects of plant growth and development, including root architecture and shoot branching. They also play a crucial role in communication between plants and symbiotic fungi or parasitic weeds.
Thigmogenesis: Thigmogenesis is the phenomenon where plants respond to mechanical stimulation, leading to changes in growth patterns or structural adaptations. This process is significant as it allows plants to adapt to their environments, particularly in response to touch or physical stress, thereby enhancing their chances of survival and reproductive success.
Thigmomorphogenesis: Thigmomorphogenesis is the process by which plants change their growth patterns in response to mechanical stimulation such as touch, wind, or rain. It involves alterations in plant structure and physiology that enhance their ability to withstand physical stress.
Thigmonastic: Thigmonastic movements are plant responses to touch or mechanical stimuli, which occur independent of the direction of the stimulus. These movements are typically rapid and can serve as defense mechanisms or aid in capturing prey.
Thigmonastism: Thigmonastism is a type of plant movement that occurs in response to touch or mechanical stimulation, characterized by a rapid and reversible change in growth direction or position. This phenomenon is particularly evident in certain plants like the Venus flytrap and Mimosa pudica, where the reaction to touch helps with survival strategies such as capturing prey or avoiding herbivory. The process is facilitated by changes in turgor pressure within specific cells, showcasing how plants can respond to environmental stimuli despite lacking a nervous system.
Thigmotropism: Thigmotropism is a growth response in plants where they turn or grow in response to physical contact with an object. This behavior allows plants to interact with their environment, facilitating support and stability, particularly for climbing species. Thigmotropism is significant as it enables plants to optimize light exposure and enhance their chances of survival by adapting to surrounding structures.
Tropism: Tropism refers to the directional growth response of a plant to an external stimulus, such as light, gravity, or touch. This adaptive behavior allows plants to optimize their growth and development based on environmental cues, enhancing their chances of survival and reproduction. Different types of tropisms enable plants to move toward or away from stimuli, facilitating important processes like photosynthesis and nutrient uptake.