9.1 4 Chemical Control Systems In Plants Flashcards
Plants are sensitive
To light
In terms of direction , light intensity and length of daily exposure to light
Light affects how much
Plants grow , the direction of growth and when they reproduce
Other factors plant are sensitive to
Gravity , water and temperature and in some cases to touch and chemicals
Different parts of the plant
May react differently to the same stimulus
Shoots grow towards light where as roots grow away from it
Plants respond to
Internal chemical signals
Goals of the plant
Photosynthesis and reproduction
Plant hormones
Many act as plant growth regulators
Produced in one area of the plant and transported around the body of the plant and have an effect on cells elsewhere
Tropism
Plant growth responses to environmental cues
Other way plant hormones can affect
Differentiation and development of plant cells and processes such as fruit ripening and leaf fall
Main areas of cell division in plants
Are the meristems that occur behind the tip of the root and the shoot
Regions of cell division and cell elongation
Particularly sensitive to plant growth substances
How do chemical messengers act
Make it easier for cellulose walls to be stretched making it easier for the cells to expand and grow
Auxins
Powerful growth stimulants that are effective at low concentrations
Produced in young shoots and move down the plant
Through active transport and some calcium ions
Stem is the source of auxins
Apical dominance
Suppress the growth of lateral shoots so that one main stem grows the fastest
The more auxins transpired down the stem
The more root growth occurs
Auxins seem
To effect the ability of the cell wall to stretch
IAA
Made in the top of the shoot and diffuses back towards the zone of elongation
Bind to specific receptor sites on the cell surface membranes
Active pumping of hydrogen ions into the cell wall spaces
Provide optimum pH for enzymes to break bonds between adjacent cellulose microfibrils
Allows microfibrils to slide past each other easily
Keeping the walls plastic and flexible
Cells absorb water and stretch
IAA is eventually destroyed and pH restored
Side not illuminated
Contains less auxin
Light causes
Auxin to move laterally across the shoot
Shoot tip acts as a photoreceptor
More cell elongation on the dark side
Shoot bends towards the light
Once the shoot is growing towards the light
Unilateral stimulus is removed
Asymmetrical transport of auxin ends and the shoot is growing towards the light
Auxins
Diffuse away from the tip
When auxin destroyed by enzymes
Cells become rigid no further cell elongation is possible
Gibberellins
Growth regulators
Affect internodes of stems stimulating the elongation of growing cells
Promote fruit growth
Breaking dormancy in seeds and germination stimulate the formation of enzymes in seeds
Stimulate bolting a period of rapid growth and flowering
Germination
Seed absorbs water and swells
The embryo is activated
Embryo secretes gibberellin that diffuse into the aleurone layer
Causes aleurone layer to produce amylase that diffuses to the endosperm and breaks down the food stores to provide the embryo with materials for respiration and growth
Enzymes produced in response to gibberellin digest the endosperm
Products released from the endosperm are used by the embryo to make new cells and germinate
Cytokinins
Growth regulators
Promote cell division in apical meristems and the cambium through interactions with auxins
Promote lateral bud development which can overcome apical dominance of leading shoot is removed or damaged .
Cytokinins work synergistically with ethene in the abscission of leaves flowers and fruits
