39 Chapter Flashcards
Hormones
A signaling molecule that is produced in tiny amounts by one part of an organism’s body and transported to other parts, where it binds to a specific receptor and triggers responses in target cells and tissues.
Etiolation
Morphological adaptations for growing in darkness
De-etiolation (greening)
Occurs when a shoot reaches light
Stages of cell-signal processing
Reception, transduction, and response
Receptors
Proteins that undergo changes in shape in response to a specific stimulus
Second messengers
Small molecules and ions in the cell that amplify the signal and transfer it from the receptor to other proteins that carry out the response.
Two main mechanisms by which a signaling pathway can enhance an enzymatic step in a biochemical pathway:
Post-translational modification
Transcriptional regualtion
Post-translational modification
Activates preexisting enzymes
Transcriptional regulation
Increases or decreases the synthesis of mRNA encoding a specific enzyme
Many signal transduction pathways ultimately regulate the synthesis of new proteins by turning specific genes on or off.
True
Protein phosphatases
Enzymes that dephosphorylate specific proteins
Plant hormones are AKA…?
Plant growth regulators
Auxin (IAA) primary site of synthesis
Shoot apical meristems and young leaves
Auxin (IAA) Major Functions
Stimulates stem elongation (low concentration only); promotes the formation of lateral and adventitious roots; regulates development of fruit; enhances apical dominance; functions in phototropism and gravitropism; promotes vascular differentiation; retards leaf abscission
Cytokinins primary site of synthesis
Roots
Cytokinins Major Functions
Regulate cell division in shoots and roots; modify apical dominance and promote lateral bud growth; promote movement of nutrients into sink tissues; stimulate seed germination; delay leaf senescence
Gibberellins (GA) Primary site of synthesis
Meristems of apical buds and roots, young leaves, and developing seeds
Gibberellins (GA) Major Functions
Stimulates stem elongation, pollen development, pollen tube growth, fruit growth, and seed development and germination; regulate sex determination and the transition from juvenile to adult phases
Abscisic acid (ABA) Primary site of synthesis
Unknown, but is present in every major organ and living tissue; it may be transported in the phloem or xylem
Abscisic acid (ABA) Major functions
Inhibits growth; promotes stomatal closure during drought stress; promotes seed dormancy and inhibits early germination; promotes leaf senescence; promotes desiccation tolerance
Ethylene Primary site of synthesis
This gaseous hormone can be produced by most parts of the plant
Ethylene Major functions
Promotes ripening of many types of fruit, leaf abscission, and the triple response in seedlings (inhibition of stem elongation, promotion of lateral expansion, and horizontal growth); enhances the rate of senescence; promotes root and root hair formation; promotes flowering in the pineapple family
Brassinosteroids Primary site of synthesis
Present in all plant tissues
Brassinosteroids Major Functions
Promote cell expansion and cell division in shoots; promote root growth at low concentrations; inhibit root growth at high concentrations; promote xylem differentiation and inhibit phloem differentiation; promote seed germination and pollen tube elongation
Jasmonates Primary site of synthesis
Derived from the fatty acid linolenic acid; produced in several parts of the plant and travel in the phloem.
Jasmonates Major functions
Regulate a wide variety of functions, including fruit ripening, floral development, pollen production, tendril coiling, root growth, seed germination, and nectar secretion; also produced in response to herbivory and pathogen invasion
Strigolactones Primary site of synthesis
Are carotenoid-derived hormones produced in roots
Strigolactones Major Functions
Promote seed germination, control of apical dominance, and the attraction of mycorrhizal fungi to the root
Tropism
Any growth response that results in plant organs curving toward or away from stimuli
Phototropism
The growth of a shoot toward light or away from it
-positive phototropism - move toward
-negative phototropism - move away
Polar transport
The unidirectional transport of auxin
Expansins
Proteins that break the cross-links (hydrogen bonds) between cellulose microfibrils and other cell wall constituents, loosening the wall’s fabric.
Senescence
The programmed death of certain cells or organs or the entire plant
Photomorphogenesis
Describes events in plant growth and development triggered by light
Action spectrum
A graph which depicts the relative effectiveness of different wavelengths of radiation in driving a particular process, such as photosynthesis.
Action spectra reveal that red and blue light are the most important colors in regulating a plant’s photomorphogenesis.
True
Blue-light photoreceptors
Photoreceptors (pigments) that absorb mostly blue light
Phytochromes
Photoreceptors that absorb mostly red light
Photoperiodism
A physiological response to photoperiod, such as flowering
Short-day plant
A plant that flowers only when the light period is shorter than a critical length
Long-day plants
A plant that flowers only when the light period is longer than a critical length
Day-neutral plants
Plants that are unaffected by photoperiod and flower when they reach a certain stage of maturity
Vernalization
The use of pretreatment with cold
Florigen
The hypothetical signaling molecule for flowering
Gravitropism
A plants responses to gravity
-Roots display positive gravitropism
-Shoots display negative gravitropism
Statoliths
Dense cytoplasmic components that settle under the influence of gravity to the lower portions of the cell
Thigmomorphogenesis
Refers to the changes in form that result from mechanical perturbation.
Thigmotropism
A directional growth in response to touch
Action potentials
Electrical impulses Used as a form of internal communication
Abiotic
Nonliving
Heat-shock proteins
Help protect other proteins from heat stress
First line of a plant’s immune defense
PAMP-triggered immunity
Pathogen-associated molecular patterns (PAMP)
Molecular sequences that are specific to certain pathogens
Effectors
Pathogen-encoded proteins that cripple the host’s innate immune system
Plant’s second level of immune defense system
R (resistance) genes
Effector-triggered immunity
The activation of R proteins by a specific effector
Hypersensitive response
Refers to the local cell and tissue death that occurs at and near the infection site
Systematic acquired resistance
Arises from the plant-wide expression of defense genes.
