Chemical and Nervous Control (Plants)
Cards (17)
- Plant Hormones and Sensory Systems
- A plant’s sensory response to external stimuli relies on chemical messengers (hormones).
- Hormones regulate a variety of plant behaviors in response to different stimuli:
- Part 1 - hormones that initiate and regulate plant behaviors
- Part 2 - stimuli that provoke these responses
- Auxins
- the main hormones for plants that are responsible for cell elongation in phototropism and gravitropism.
- Apical dominance is triggered by auxins produced in the apical meristem; flowering, fruit ripening, and leaf abscission are other plant responses under the control of auxins.
- Cytokinins
- they promote cytokinesis (cell division); they are most abundant in growing tissues, such as roots, embryos, etc, where cell division is present.
- They delay senescence (aging) in leaf tissues, promote mitosis, and stimulate differentiation in the meristem in shoots and roots.
- Gibberellins (GAs)
- group of about 12 closely related plant hormones that stimulate shoot elongation, germination, and fruit and flower maturation.
- Abscisic acid (ABA)
- causes the abscission of leaves.
- they accumulate as a response to stressful environments; it counteracts many of the growth-promoting effects of GAs and auxins.
- Ethylene
- promotes fruit ripening, flower wilting, and leaf fall; it is a volatile gas (C2H4).
- Agining tissues and nodes of stems produce ethylene.
- Systemin
- it is distributed systemically in the plant body upon production and activates plant responses to wounds from herbivores.
- They initiate the production of compounds, like jasmonic acid, which has a bad taste and inhibits the digestion of herbivores.
- Methyl Salicylate (MeSa)
- helps regulate responses to infection by parasites or pathogens.
- When a foreign organism infects a cell, there is a response called the hypersensitive response (HR), and then the plant initiates a response called systemic acquired response (SAR).
- Plant Response to Light
- Plants are generally capable of detecting and responding to at least three wavelengths of light: blue, red, and far-red light.
- They are detected by photoreceptors, that are composed of a light protein covalently bonded to a chromophore light-absorbing pigment. Together, they are called a chromoprotein.
- Plant Response to Light
- Phototropism - the movement of plants toward or away from the light.
- Stem Elongation - growth of plants
- Germination - seed sprouting in plants
- Photoperiodism - flowering in response to length of day.
- Plant Growth Response
- Apical Dominance - many plants grow primarily at a single apical meristem and have limited lateral branches.
- Leaf Abscission - some plants drop leaves in response to changing season
- Fruit Growth - the growth of fruits in size is promoted by GAs
- Fruit Ripening - once the fruits have grown, they begin to ripe; the process is stimulated by ethylene.
- Plant Response to Water or Water Stress
- Germination - the seeds of some plant species rely on the imbibition of water to initiate germination.
- Stomatal Closing - the activation of Phot 1 and Phot 2 by blue light causes stomata to open and permit gas exchange.
- Local Cell Death - In drought, the immediate response is the closing of stomata. However, if the stomata in plants are closed for too long, the plants will die.
- Plant Response to Touch
- Thigmotropism is movement in response to touch. It is characterized into two types:
- Slow Thigmotropism
- Fast Thigmotropism
- Slow Thigmotropism
- plant response to a touch stimulus that affects its direction of growth. (Vines that wrap around sticks)
- Fast Thigmotropism
- the rapid response to touch such the way the Venus flytrap snaps shut to trap an insect or mimosa plants clamp their leaves.
- Phototropins
- chromoproteins that are responsible for mediating the phototropic response.
- Amyloplasts
- it is also known as statoliths which are specialized cellular compartments containing starch granules that move in response to gravity.