Plant Responses to Internal and External Signals — Vocabulary Flashcards

A set of vocabulary flashcards summarizing essential terms and concepts from Campbell Biology Chapter 39 on plant responses to internal and external signals.

Phytochrome

A red/far-red light photoreceptor that switches between Pr and Pfr forms to regulate germination, shade avoidance, and de-etiolation.

De-etiolation (Greening)

The suite of morphological and biochemical changes that occur when a dark-grown seedling is exposed to light.

Plant Hormone

A small organic molecule produced in low concentration that triggers specific developmental or physiological responses in target cells possessing the appropriate receptor.

Signal Transduction

The process by which a receptor converts a stimulus into a cellular response, often involving secondary messengers and protein kinases.

Reception (in plants)

Detection of an internal or external signal by a receptor protein located in the plasma membrane, cytosol, or nucleus.

Response (in plants)

The physiological or developmental change that results from a signal transduction pathway.

Secondary Messenger

An intracellular signaling molecule (e.g., Ca²⁺, cGMP) that amplifies and relays the signal from the receptor to target molecules.

Calcium Ions (Ca²⁺)

A common secondary messenger in plant cells that helps activate protein kinases during signaling cascades.

Auxin (Indole-3-acetic acid, IAA)

A hormone produced mainly in shoot apical meristems and young leaves that promotes cell elongation, phototropism, gravitropism, and apical dominance.

Acid Growth Hypothesis

Model stating that auxin activates proton pumps that acidify cell walls, loosening them and allowing turgor-driven cell elongation.

Phototropism

Growth of a plant organ toward or away from light, typically mediated by differential distribution of auxin.

Gravitropism

Directional growth in response to gravity; shoots show negative gravitropism, roots positive.

Apical Dominance

Inhibition of lateral bud growth by the presence of an active shoot tip producing auxin and sugars.

Cytokinins

Hormones synthesized mainly in roots that stimulate cell division, delay senescence, and work antagonistically with auxin in apical dominance.

Gibberellins (GAs)

Hormones that promote stem elongation, seed germination, and pollen tube growth; used to loosen grape clusters.

Abscisic Acid (ABA)

A hormone that induces stomatal closure, seed dormancy, and drought tolerance by reducing water loss.

Ethylene

A gaseous hormone that promotes fruit ripening, leaf abscission, and the triple response in seedlings.

Strigolactones

Hormones that inhibit axillary bud growth and promote mycorrhizal associations; underproduction leads to bushy phenotypes.

Apoplastic Transport

Movement of substances through cell walls and intercellular spaces without crossing plasma membranes.

Symplastic Transport

Movement of substances through plasmodesmata, staying inside the cytoplasm of adjacent cells.

Thigmotropism

Directional growth in response to touch, involving rapid ion fluxes (notably K⁺) and turgor changes.

Circadian Rhythm

An internal, approximately 24-hour biological cycle that regulates processes such as leaf movements and stomatal opening.

Photoperiodism

Physiological response to relative lengths of day and night, often regulating flowering and dormancy.

Short-Day Plant

A plant that flowers when nights exceed a critical length; flowering promoted by long, uninterrupted darkness.

Long-Day Plant

A plant that flowers when nights are shorter than a critical length; flowering promoted by brief night interruptions with red light.

Systemic Acquired Resistance (SAR)

Long-lasting, broad-spectrum immune response that occurs in tissues distant from an initial infection site.

Hypersensitive Response

Localized plant defense that includes rapid cell death around an infection site to restrict pathogen spread.

Heat-Shock Proteins

Molecular chaperones synthesized under heat stress that protect other proteins from denaturation.

Statoliths (Amyloplasts)

Starch-filled plastids that settle to the lower sides of root cap cells, helping roots sense gravity.

Phototropins

Blue-light receptor proteins that mediate phototropism and chloroplast movements.

Blue Light

The wavelength range most effective at inducing phototropic curvature and chloroplast relocation.

Red Light

Wavelength that converts phytochrome to its active Pfr form, stimulating seed germination and other responses.

Far-Red Light

Wavelength that converts Pfr back to Pr, inhibiting responses like germination when dominant.

Seed Light Requirement

Some seeds germinate only when exposed to red light because phytochrome in the Pfr form promotes germination.

Shade Avoidance

Growth response triggered by a low red:far-red ratio, leading to stem elongation to outgrow competitors.

Drought Tolerance (ABA pathway)

Process in which increased ABA causes stomatal closure, reducing transpiration and water loss.

Triple Response

Ethylene-induced slowing of stem elongation, stem thickening, and horizontal growth to navigate around obstacles.

Chloroplast Relocation

Movement of chloroplasts to the cell sides receiving most light, maximizing photosynthesis under blue light.

Secondary Compounds

Metabolites such as alkaloids, terpenoids, and phenolics that deter herbivores and defend against pathogens.

Phytoalexins

Antimicrobial compounds synthesized by plants at infection sites as part of defense responses.

Salicylic Acid

Signaling molecule involved in SAR; pathogens that degrade it (via salicylate hydroxylase) become more virulent.

Heat Stress Response

Plant adaptation involving synthesis of heat-shock proteins and sometimes evaporative cooling via stomata.

Cold Stress Response

Accumulation of solutes (e.g., sugars) that lower freezing point and protect cells against ice crystal damage.

Volatile Signal Compounds

Airborne chemicals (e.g., jasmonates) released by wounded plants to warn neighboring tissues or plants of herbivory.

Protein Kinase

An enzyme that phosphorylates proteins, a common component of signal transduction cascades in plants.

Receptor Protein

Molecule that specifically binds a signal (hormone, light, touch) and initiates a cellular response.