Plant Responses
- Created by: crazycatthing
- Created on: 06-02-17 12:54
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- Plant Responses
- Types of plant responses
- avoiding herbivory
- some plants (e.g. oak) produce tannins which are toxic to micro-organisms and herbivores
- can also act as a chemical signal to tell other plants to produce tannins
- herbivory is the consumption of plants
- some plant produce alkaloids which are bitter and therefore deter herbivory
- plants like the sensitive mimosa plant have leaves which fold up in response to touch, scaring away the insects
- some plants (e.g. oak) produce tannins which are toxic to micro-organisms and herbivores
- abiotic stress
- shortage of water
- reduce water loss through closing stomata, coordinated by hormones especially abscisic acid
- tropisms - directional growth movement
- phototropism - response to light
- shoots display positive phototropism
- geotropism - response to gravity
- shoots show negative geotropism
- roots show positive geotropism
- chemotropism - response to certain chemicals
- pollen tube shows positive chemotropism as it grows towards ovum during reproduction
- thigmotropism - response to touch
- certain plants, like ivy, grow so that their stem (or branch) winds around a support
- phototropism - response to light
- shortage of water
- avoiding herbivory
- Plant Hormones
- seed germination
- gibberellin is activated when seed takes up water
- gibberellin travels to aleurone layer
- gibberellin stimulates the production of amylase which hydrolyses starch to glucose
- glucose provides a substrate for respiration and photo-synthesis and protein synthesis in the embryo so it can start to grow
- gibberellin is activated when seed takes up water
- leaf loss (abscission) in deciduous plants
- region of cells at end of leaf called abscission zone
- auxin produced in then leaf inhibits abscission by making the cells insensitive to ethylene
- when auxin concentration drops, the cells in abscission zone become sensitive to ethylene, stimulating production of celluiase enzyme in the abscission zone
- cellulose digests the cell walls in the abscission zone, making the leaf drop
- when auxin concentration drops, the cells in abscission zone become sensitive to ethylene, stimulating production of celluiase enzyme in the abscission zone
- cytokinins enter the leaf and stop the leaf from senescing (aging and turning brown)
- when concentration of cytokinins drops the leaf ages and the production of auxin in the leaf
- when auxin concentration drops, the cells in abscission zone become sensitive to ethylene, stimulating production of celluiase enzyme in the abscission zone
- cellulose digests the cell walls in the abscission zone, making the leaf drop
- when auxin concentration drops, the cells in abscission zone become sensitive to ethylene, stimulating production of celluiase enzyme in the abscission zone
- when concentration of cytokinins drops the leaf ages and the production of auxin in the leaf
- region of cells at end of leaf called abscission zone
- stomatal closure
- guard cells possess receptors for abscisic acid and control the opening and closing of stomata
- when abscisic acid binds to the receptors a number of chemical pathways inside the cell are activated, leading to an increase in pH and the transfer of calcium ions from the vacuole to the cytoplasm
- calcium stimulates loss of charged ions from the cell, increasing the water potential so that water leaves the cell via osmosis
- cell becomes more flaccid and therefore stomata close
- calcium stimulates loss of charged ions from the cell, increasing the water potential so that water leaves the cell via osmosis
- when abscisic acid binds to the receptors a number of chemical pathways inside the cell are activated, leading to an increase in pH and the transfer of calcium ions from the vacuole to the cytoplasm
- guard cells possess receptors for abscisic acid and control the opening and closing of stomata
- seed germination
- Experimental Evidence
- auxin and apical dominance
- auxin is produced at the tip of the shoot and inhibits the growth of lateral buds
- removal of apical bud allows lateral buds to grow
- if auxin or synthetic auxin is placed on a cut tip of a shoot, lateral bud growth is inhibited
- more recent evidence shows that this link may not be direct because auxin stimulates the production of abscisic acid which inhibits lateral bud growth
- auxin is produced at the tip of the shoot and inhibits the growth of lateral buds
- gibberellins and stem elongation
- growing seedlings with certain fungi (from which gibberellins can be isolated) increases seedling growth via greater elongation of the stem
- applying a cream containing gibberellins to fungi causes stem elongation
- gibberellins and seed dormancy
- early germination can be caused by application of gibberellins to a seed
- inhibiting gibberellins can prevent early germination (abscisic acid inhibits seed germination)
- auxin and apical dominance
- Commercial uses of plant hormones
- gibberellins
- delay fruit senescence (aging) and drop to make harvesting easier
- improve fruit shape and size
- activate enzymes stored in barley to produce malt for brewing
- speed up seed production in breeding programmes
- ethene
- spped up fruit ripening and promote fruit drop
- promote growth of lateral branches
- auxins
- promote root growth in cuttings
- produce seedless fruit
- selective weedkiller
- cytokinins
- delay leaf senescence to avoid discolouring of vegetables
- promote bud and shoot growth during tissue culture
- promote growth of lateral buds
- gibberellins
- Types of plant responses
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