Introductory Crop Physiology

TYPES AND USE OF ANTITRANSPIRATION

Types and uses of antitranspirants

• The chemicals or substances applied to the transpiring surface with the aim to reduce transpiration are called antitranspirants.
• Antitranspirants will reduce transpiration without reducing the assimilation rate
Examples: ABA (5 to 10 ppm), CCC (1000 ppm), Alar (200 ppm), Simazine (50 ppm), Silicon (100 ppm), etc

There are three types of antitranspirants.

i) Stomatal closing type

• These antitranspirants reduce the closure of stomata and reduce the rate of transpiration.
• Since the stomata are made to close, the rate of CO2 diffusion into the leaf is also reduced leading to low photosynthetic rates.
eg. Phenyl Mercuric Acetate (PMA), Abscisic Acid (ABA) and high CO2 concentration


• CO2 is an effective antitranspirant.
• A little rise in CO2 concentration from the natural 0.03% to 0.05% induces partial closure of stomata.
• Its higher concentration cannot be used as this result in complete closure of stomata affecting adversely, the photosynthesis and respiration.


• PMA is widely used chemical for stomatal closer.
• It has the ability to close the stomata but it has a disadvantage that it is toxic to fruits and vegetables.
• This chemical also inhibits phosphorylation and hence damages the foliage by blocking photosynthesis


• Herbicides such as triazine, atrazine, simazine which are the inhibitors of ETC at QA and QB sites but at the lower concentration they can also be used as antitranspiratns.
ii) Film forming type

• This type forms a thin film coating on the surface of leaf and inhibits the loss of water vapour from the leaf. But they allow CO2 to pass into the leaf through lower epidermis.
E.g. Waxes, Plastic films, Silicone oils

Disadvantages:

• Affects only at low temperature but not at high temperature
• Comes in the way of gas exchange.
• Form the mechanical barrier for stomatal movement

iii) Reflective type

• The principle of using this type of chemicals is to increase the light reflection by the leaves, thus decreasing the leaf temperature or head load on the leaf.
• The water loss is reduced without affecting the CO2 assimilation. E.g. Kaolinite (Kaolin), Lime water (Lime wash)
• Kaoline when applied it forms white thin film. Usually it is sprayed at 2-5 per cent and forms thin coating on the leaf
Function: Reflects radation falling on the leaf and reduces heat load on leaf. When heat load is reduced amount of water to maintain temperature is also reduced. Therefore water conservation occurs. Kaoline doesn’t come in the way of any metabolic activity.

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