16.2 Plant Responses To Abiotic Stress Flashcards
What do deciduous plants do in temperate climates
Temperate climates are always changing, for example the amount of daylight, or even the amount of wind. This can impact photosynthesis. So deciduous plants just shed their leaves in winter and remain dormant until thr days lengthen and temperatures begin to rise again
How do plants respond to day length sensitivity
It is found that plants are sensitive to lack of light. This is called photoperiodism. Before it was assumed that plants responded to the length of daylight, but more recent evidence suggests that it is lack of light that triggers change. Many plant responses are affected by the photoperiod, including the breaking of dormancy of the leaf buds so that they open up
What does the sensitivity of plants to day length result from?
A light sensitive pigment called phytochrome. This exists in two forms. Pr and Pfr. Each absorbs different types of light and the ratio of Pr to Pfr changes depending on levels of light
As summer ends and days shorten with the drop in temp, what does this cause?
A number of changes, including abscission or leaf fall and a period of dormancy during the winter months
What does the falling of light levels cause?
Falling concentrations of auxin. The leaves respond to the falling auxin concentrations by producing Ethene. A zone at the base of the leaf stalk, called the abscission zone, is made up of two layers of cells sensitive to ethene. Ethene initiates gene switching in these cells resulting in the production of new enzymes. These enzymes weaken thr cell walls outer layer of the abscission zone, called the separation layer
What happens once the separation layer is fully digested?
The vascular bundles that carry materials into and out of the leaf are sealed off and fatty acid materials are deposition on the stem side of the separation layer, forming a protective scar when the leaf falls, preventing the entry of pathogens. The hormonal cues also cause cells deep inside the separation zone to retain water and swell, straining the outer layer even more. Abiotic factors then finish the job such as strong wind, and the leaf separates, leaving a waterproof scar behind.
How do plants prevent freezing
If cells freeze in plants, they die. So they cytoplasm of the plant cells and the sap in vacuole contains solutes that lower the freezing point. Some plants also produce sugars, polysaccharides and amino acids which act as antifreeze to prevent their cytoplasms from freezing and damage. These changes happen over a sustained period of lowering body temps to prepare for frosty yute.
How do plants respond to stress via stomatal opening?
Opening stomata can cool the plant as water evaporates from the cell from the leaves in transpiration. Closing it means water can be conserved. The control of the opening and closing of the stomata in response to abiotic stress is a result of the hormone ABA
Under abiotic stress, leaf cells release ABA which causes it to close. However scientists have also found that roots also provide an early warning of water stress through ABA, which is transported to the leaves where it binds to receptors on the plasma membrane of the stomatal guard cells, inducing change, causing it to close
