Please enable JavaScript.
Coggle requires JavaScript to display documents.
Plant Co-ordination and Control - Coggle Diagram
Plant Co-ordination and Control
Stimulus and Plant Response
A stimulus is any change in an organism's environment to which they respond.
Plants mainly respond to light as a stimulus.
Plants respond to the direction and duration of light (phototropism and photoperiodism).
Photoperiodism
Is the response of a plant to the relative lengths of daylight and darkness.
Flowering is affected by the period of illumination (photoperiod).
Day Neutral Plants: Flower whenever they have grown sufficiently, regardless of daylight (e.g. Snap-Dragons, violet, begonia).
Long Day Plants (LDPs)
: Flower only if the number of hours of light they have been exposed to is above a certain level (e.g. spinach, clover, poppy, petunia, cabbage).
Short Day Plants (SDPs)
: Flower only when darkness/nights exceed a critical minimum level (e.g. chrysanthemums, strawberries).
Control of Flowering in LDPs and SDPs
The photoreceptor involved in photoperiodism is the light-sensitive pigment called phytochrome.
Phytochrome has two inter-convertible forms:
Phytochrome 660
(P660 or PR) and
Phytochrome 730
(P730 or PFR).
Long day plants flower during long summer days and need a short night.
Short day plants are winter-flowering or live near the equator and need a long night.
The plant measures the length of day or night by monitoring the relative concentrations of PR and PFR.
Manipulation of the photoperiod can be used to control flowering in plants.
Manipulating LDPs and SDPs
Flowering in LDPs is stimulated by increasing day length.
Flowering in SDPs is inhibited by high levels of PFR.
The length of the night/dark period is critical in determining whether flowering occurs in both LDPs and SDPs.
Photoperiod manipulation can be used to bring forward or delay the flowering period.
Plant Growth Substances (PGS) and Stem Elongation
Plant growth is coordinated by plant growth substances (PGS).
The three main groups of PGS that affect growth in stems are auxin, gibberellins, and cytokinins.
Different PGS can work together or against each other to affect plant growth.
Auxin Action
Found predominantly at the growing tip of the stem (apical meristem).
Promotes cell elongation in the zone of elongation.
Produced in the cells of the apical meristem and diffuse or are actively transported down the shoot.
Bind to specific receptors on the cell surface membranes of newly formed cells.
This causes the cell surface membrane to pump hydrogen ions out into the cellulose cell wall, making it more flexible.
The cells absorb water by osmosis and expand/elongate.
Gibberellins
Promote growth of internodal regions by cell elongation.
They are produced in seeds, young leaves, and young apical tissue.
Also affect cell elongation in dwarf plants.
When sprayed on plants, gibberellins can initiate normal plant growth.
Cytokinins
Are produced in meristematic tissues in the zone of division.
Promote growth by stimulating cell division.
Interacts with other hormones such as auxin and gibberellins.
The interaction of cytokinins with other hormones can be exploited in micro-propagation.