Topic 9 Flashcards
Which stimuli affects plants?
Variety, most which are external factors that have a direct impact on the well being of the plant.
Very sensitive to light, and respond to the direction of light and the length of daily expose to it, also affects how much they grow and when the reproduce. Also sensitive to gravity, water and temperature.
Also affected by chemical signals
What are the plant responses?
Chemicals produced in repossessed to specific stimuli. Many act as growth regulator.
Plant hormones, produced in one area of the plant and are transported around the body of the plant and have their effects on cells elsewhere.
In some cases, growth is stimulated or inhibited.
What are tropisms?
The directional growth responses to specific environmental cues.
How do plants grow?
Permanent increase in size of an organisms. Cell division, new material within the cells. Mains areas of division in plants are the meristems and this occurs just at the tip of a root or shoot. Cell elongation and cell division are sensitive to plant growth substance
How do the growth hormones make the plant grow?
Can make it easier for the cellulose walls to be stretched and hence easier for the cell to expand and grow.
What are auxins?
Powerful growth stimulants that are effective in LOW concentrations.
Are produced in young shoots and always move DOWN the plant for, shoot to roots.
Involves active transport and calcium ions,
Why is auxin involved with apical dominance?
Where they suppress the growth of lateral shoots so that one main stem can grow fastest
The more auxin is transported down the stem…
… the more root growth occurs
What happens if the tip of the stems in plants are removed
Removes the source of auxin, the stimulation of root growth is removed and root growth slows and stops completely.
What are auxins involved with other than growth?
Tropic response of plant shoots in unilateral light. The response of the plant to auxins often depends on both th concentration of th hormone and the region of the plant.
How do auxins work in a plant ?
Seem to affect the ability of the plant cell walls to molecules bind to specific receptor sites on the cell surface membrane, activating the active pumping of hydrogen ions into the cell wall spaces. Changes hydrogen ion conc, providing optimum pH of 5 for enzymes that break bones between adjacent cellulose microfibrils.
Cells absorb water by osmosis and turgor pressure is caused , walls stench to allow cells to elongate,
Why does the bonds of microfibrils in a cell wall have an impact on growth?
Allows microfibrils to slide past each other very easily, keeping walls flexible.
How is IAA destroyed?
By enzymes, as the cells mature. The pH of the cell wall rises and the enzyme is inhibited and bonds form between the cellulose microfibrils. As a result, the cell wall becomes more rigid and cell can’t expand,
How does light have an affect of auxins?
side of a shoot exposed to light contains less auxin than the side which isn’t illuminated.
Light seems to cause auxin to move laterally across shoot, greater concentration on the illuminated side. Movement means shoot tip acts as a photoreceptor.
How does cell elongation come about with auxins and light?
More hormone diffuses don the region of cell elongation on the dark side, which simulated cell elongation and therefore growth on the dark side. Once shoot is growing directly towards the light, the unilateral stimulus is removed,
What is gibberellins?
Growth regulators. Affect the internodes of stem and stimulate elongation of the growing cells,
Also promote the growth of fruit.
How do giberellins work?
Involve breaking down dormancy In seeds and in germination. Stimulate the formation of enzymes in seeds. Eg, stimulate amylose which breaks down starch storages. Makes glucose available for the embryo as it developed as the seed germinated.
Also used for bolting, a period of sudden rapid growth and flowering
What are cytokinins
Growth regulators that promote cell division in the apical meristems and the cambium through interactions with auxins.
How to cytokinins work
Promote lateral bud development, which can overcome, apical dominance if the leading shoots in removed or damaged.
Works synergistically with ethene in the abscission of leaves, flowers and fruits
What is synergy and antagonism?
When plant hormones work in interaction with other substances, means that very fine control over the responses of the plant can be achieved.
If they work together, they complement each other, called synergy, like auxin and gibberellins
If they have opposing effects, they balance will determine the response of the plant.
What is apical dominance
The balance between auxin and cytokinins is very important in overall development of the plant. Maintenance of apical dominance is main importance
One leading shoot grows bigger and faster than the other, and growth of all other lateral buds is inhibited, as a result of high auxin, first shoot emerges. The auxin acts antaginositcally with cytokinins which stimulates the development in lateral buds.
First shoot grows away and inhibition of auxin is reduced and ctuokinin becomes dominant.
What are the sensory systems in plants?
Seeds grown if exposed to light, but only red light. If exposed o far red light, won’t germinate. It’s the last light it’s exposed to that determines if it grows or not. This is called phytochrome.
What are phytochromes?
Plants make number of phytochromes, but all respond to light in same way.
When one form of the pigment absorbed light, it is converted reversibly into the other form. As a seed breaks through soil and exposed to red light, it makes far red light.
The length of time it takes to convert depends on the light intensity.
What is the most stable light for plants?
Red light is the more stable pigment
