- Leaf modifications such as formation of prickles, leaf spines, phyllodes etc., help in reducing the rate of
transpiration. - Compact mesophyll reduces transpiration while a loose mesophyll increases transpiration.
- Presence of mucilage decreases the rate of transpiration by holding water.
Wilting
Wilting is the loss of turgidity of leaves and other soft aerial parts of a plant causing their drooping, folding and rolling.
The symptoms of wilting are not shown by thick-walled tissues. Therefore, they are less conspicuous in sclerophyllous
plants. Wilting is of 3 types : incipient wilting, temporary or transient wilting and permanent wilting.
In incipient wilting, there are no external symptoms of wilting but the mesophyll cells have lost sufficient water
due to transpiration being higher than the availability of water. It occurs during mid day for a brief period in almost
all plants even when sufficient water is present in the soil. Temporary or transient wilting is the temporary drooping
down of leaves and young shoots due to loss of turgidity during noon. Lower leaves show wilting earlier than the
upper ones. Temporary wilting is corrected only after the rate of transpiration decreases in the afternoon accompanied
by replenishment of water around the root hairs. A permanent wilting is that state in the loss of turgidity of leaves
when they do not regain their turgidity even on being placed in a saturated atmosphere. It occurs when the soil
is unable to meet the requirement of plant for transpiration. After permanent wilting, the plant dies.Transpiration as necessary evil
Transpiration causes loss of huge amount of water absorbed by plants and leads to wilting and injury in plants. It
also checks photosynthesis, reduces growth and if too severe, may cause death due to desiccation.
Inspite of various detrimental effects, the plants cannot avoid transpiration due to their peculiar structure of leaves
which is basically meant for gaseous exchange during respiration and photosynthesis and also for the required pull
for ascent of sap. Therefore, transpiration is also regarded as “necessary evil” by Curtis (1926) or “unavoidable
evil” by Steward (1959).Antitranspirants
Plant antitranspirants are chemical substances, whether naturally
synthesised by plants themselves or synthetic materials applied
to plants, which reduce the rate of transpiration effectively.
An ideal antitranspirant is one which decreases the transpiration
rate without affecting CO 2 fixation in photosynthesis. There are
two types of antitranspirants: metabolic inhibitors and surface
films. Metabolic inhibitors reduce transpiration by reducing