Plant Responses To Different Abiotic Stresses At Different Times Of Year Flashcards
Why is it useful for deciduous plants to lose their leaves in the winter?
-shorter days and lower light intensity = less photosynthesis and glucose production
-becomes insufficient to keep leaves as they use glucose for respiration but don’t produce lot
-trees with leaves are more likely to be damaged in heavy rain and wind
-reduces water loss by transpiration
How do plants actually respond to photoperiod (day length)?
-reduced light intensity results in less auxin
-leaves respond to lower auxin concentration by producing more ethene
-base of leaf stalk contains 2 layers of cells sensitive to ethene (abscision layer)
-ethene switches on genes to make new enzymes
-these enzymes weaken cells in the outer layer of abscision zone (separation layer)
-lipid deposits are laid down on the other side to form a protective layer
-abiotic factors such as wind and rain put strain on the separation layer and the leaves fall off
-this leaves a lipid waterproof scar left behind on leaf stalk, which prevents pathogens from entering stalk and sap leakage
Why would it matter if plant cells freeze?
-disruption to membrane structure (ice crystals damage bi layer)
-damage to enzymes
-cell death
What mechanisms have plants evolved to protect their cells in freezing conditions?
-cytoplasm and vacuole sap contain solutes which lowers the freezing point of water
-in winter some plants produce extra sugars, amino acids etc which act as anti freeze. This is triggered by ABA switching on specific genes for the production of these chemicals
How does stomatal control (controlled by ABA) help plants respond to stress?
-when stomata are open, helps plants to cool down due to transpiration
-when stomata are closed, this conserves water, useful in droughts
How does the plant hormone Abscisic acid actually control the opening and closing of the stomata in leaves by guard cells?
1) ABA binds to receptors on the cell surface membrane of guard cells (specific complementary shape)
2) calcium channels open, so calcium ions enter, and the pH of the cytoplasm is raised
3) these events cause potassium ions, nitrate ions and chloride ions to leave the cell
4) as a result the water potential of the cell increases and water is moved by osmosis into surrounding cells. The resulting loss of turgor causes the stomata to close
How are plant hormones used commercially to ripen fruit?
-gaseous plant hormone ethene involved in ripening of climacteric fruits (continue to ripen after harvesting)
-peak of ethene production triggers a series of chemical reactions including greater respiration rate
-an example is placing one ripe banana in a bag of green bananas, these will ripen faster as the ethene from the ripe banana stimulates the rapid ripening of the green ones
-climacteric fruits are harvested once fully formed but long before they are ripe. Un ripe fruit is are and much less easily damaged during transport around the world. When fruit is needed for sale they are exposed to ethene gas under controlled conditions
-prevents fruit wastage during transport and increases time available for them to be sold
How are plant hormones used commercially in rooting powders?
-auxin is the plant hormone that affects growth of both shoots and roots
-by applying auxin to cut shoots it stimulates the production of roots, making it easier to propagate new plants from plant cuttings
-important for both horticulture and agriculture as many plants can be propagated on a large scale by micropropagation
How are plant hormones used commercially in weed killers?
-weeds are plants that grow where they are not wanted, and they may interfere with crop plants competing for light, space, water and minerals
-if synthetic dicot auxins are applied as weed killer they are absorbed by the broad-leaved plants and affect their metabolism. Growth rates increases and becomes unsustainable so they die
-synthetic auxins used by farmers and gardeners are simple and cheap to produce, have a very low toxicity to mammals.
