Download salt regulation in plants

MAINTAINING A BALANCE
SALT REGULATION IN PLANTS
Read the passage below and answer the questions.
Most plants cannot tolerate salty conditions; in saline environments the solute concentration in the
soil is greater than it is inside the plant’s roots, and so water tends to move out by osmosis. In
addition, an excess of sodium ions inside cells inhibits enzyme activity and can result in a decrease in
the uptake of essential potassium ions.
Some plants, however, have successfully inhabited areas of high salinity such as deserts, salt marshes
and coastal areas. They are known as halophytes, and all possess various adaptations to assist them in
surviving high salt levels in their surroundings.
Some halophytic plants, such as certain mangrove species, are capable of actively pumping sodium
ions out of their roots and transporting potassium ions in. The presence of calcium ions in the soil
seems to be a requirement for this process to occur. Other plants are able to take in sodium ions and
then either secrete them or isolate them from the rest of the functioning plant cells. In the salt marsh
plant, Sarcocornia quinqueflora, salt is accumulated in swollen leaf bases that are then shed from the
rest of the plant. Some Australian mangroves can also store excess salt in leaves that are subsequently
dropped. Similarly, sodium ions in Atriplex (saltbush) are concentrated in salt glands within the leaf
and pumped into bladders that eventually expand and burst, releasing the excess salt. In Distichlis
palmeri (Palmer’s grass), salt leaves the plant through cells in the leaf, builds up on the leaf surface
and is ultimately washed away. The grey mangrove, Avicennia marina, and the salt marsh plant,
Sporobolus virginicus, also excrete salt through salt glands on their leaves.
Plants exposed to salty air may possess mechanisms to prevent salt entering their leaves; a thin layer
of cuticle for this reason covers the stomates of the Norfolk Island pine.
1)
What is a halophyte?
2)
Give three reasons why most plants cannot survive in areas of high salinity.
3)
What needs to be present in the soil before sodium ions can be pumped out of the roots of
some plants? Name a plant that can get rid of excess salt in this manner.
4)
Name two halophytic plants that can accumulate salt in leaves that they subsequently shed.
5)
Describe the unique way in which Atriplex plants dispose of excess salts.
6)
In what way do both the grey mangrove and Sporobolus rid themselves of salt?
7)
Describe one way in which the Norfolk Island pine has adapted to salty conditions.
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TITAN EDUCATION - BIOLOGY