Anti-transpirants and it’s Classification



Antitranspirants are substances or chemicals applied on plant-foliage to control rate of transpiration. The important points to be considered in using antitranspirants are:

(a) They should restrict water loss from leaf surface without restricting entry of carbon dioxide for photosynthesis, and

(b) Transpiration necessary for cooling of leaf surface should not be completely stopped by the application of antitranspirants leading to rise in leaf temperature.

Based on their mechanism of action, antitranspirants are classified into various types.

Stomatal closing type: They cause partial or complete closure of stomata by inducing the guard cells to close. But complete closure of stomata adversely affects gas exchange and photosynthesis. These chemicals may also cause phyto-toxicity and are very expensive too. E.g., Phenyl mercuric acetate (PMA) and alkanyl succinic acid (ASA).

Film forming type: They cover the stomata by forming a thin film over leaf surface. These substances are nontoxic, non-degradable and very easy to apply but they adversely affect photosynthesis. E.g., Paraffin and wax emulsions, folic 2%, and power oil 1%.

Reflectant type: When sprayed on leaf surface, the reflectant type antitranspirants increase the leaf albedo or leaf reflectance of sunlight. As a result, heating is reduced, leaf temperature inside is low and need for transpiration is reduced. E.g., Kaolin and lime solution. Spraying kaolin at 3–6% concentration reduced leaf temperature by 3–4 °C and transpiration by 22–28%. These are less expensive, non phytotoxic and do not interfere with photosynthesis, since stomatal closure does not take place.

Growth retardant type: Chemicals like cycocel (ccc-chloro choline chloride, chlor mequat) when sprayed on foliage, reduce leaf area and thereby reduce the transpiring area and transpiration.

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