Antitranspirants and its Role in Agriculture
Authors: Sneha kumari, Jyoti Chauhan


Transpiration from plants and evaporation from soil surface are the two main sources of water loss from vegetated fields. However, under arid conditions where soil moisture conditions are critical, water loss may not be very high from sandy soils after the drying of the top layer. In recent years only, more attention has been paid for exploring the possibility of reducing transpiration from plants by the use of chemicals. These antitranspirants may control transpiration either by filming the leaf surface or by the regulation of stomatal aperture.

Introduction

Antitranspirants are the materials or chemicals which decrease the water loss from plant leaves by reducing the size and number of stomata. Nearly 99 per cent of the water absorbed by the plant is lost in transpiration. Antitranspirants are chemical compounds, their role is to practice plants of hardening to stress, as a method of reducing the impact of drought due to salinity. Reducing the transpiration can play a useful role in this respect by preventing the luxurious loss of water to atmosphere via stomata. Recently, efforts have been made to find substances, which when applied to the plant, reduce transpiration, i.e. antitranspirant materials. However, since the processes of transpiration and photosynthesis involve the passage of water vapor and carbon dioxide via the stomata, both processes may be affected when these stomata were narrowed or curtailed by antitranspirants application.

Antiranspirants and is any natural applied to transpiring plant surfaces for reducing water loss from the plant. There are of four types.

1. 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.

2. 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

3. Reflectance 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.

4. Growth retardant:

These chemicals reduce shoot growth and increase root growth and thus enable the plants to resist drought. They may also induce stomatal closure. Cycocel is useful for improving water status of the plant.

Antitranspiratnts are also useful for reducing transplantation shock of nursery plants of Horticultural plants:

• Metabolic inhibiter like phenyl mercuric acetate, some alkanyl succinic acids.
• Growth retardant such as A.B.A. Cycocel.
• Herbicides, fungicides
• Salicylic acid.
• Colourless plastics, silicon oil, wax or plastic.
• White reflecting materials (e.g. Kaolin) emulsions or white wash.

Good features of antitranspirants:

• Non toxicity
• Non-permanent damage to stomata mechanism.
• Specific effects on gard cells and not to other cells.
• Effect on stomata should persist at least for one week.
• Chemical or material should be cheap and readily available.

Role of antitranspirants in annual field crops:

In general field crops are highly dependent or current photosynthesis for growth and final yield. Therefore it is unlikely that currently available antitranspirant would increase yield of an annual crop unless crop suffers stressed from inadequate water and or a very high evaporative demand, particularly during a moisture sensitive stage of development. Fuahrin sprayed stomata inhibiting or film forming antitranspirants on field grown sorghum under limited irrigation conditions, he found that grain yield increases 5 to 17% and application of antitranspirant just before the boot stage was more effective than later sprays.

References

Asha, Y. and A. Yahya, 1998. Responses to salinity of sesame (Sesamum indicum L.) and sugar beet (Beta vulgaris. L.) Department of Plant Biology, Swedish University of Agricultural Sciences, S-750, Uppsala, Sweden. No., 122.

Asch, F., M. Dingkuhm and K. Dorffling, 2000.Salinity increase CO assimilation but reduces growth in field grown irrigated rice. West Africa Rice Development Association, 1. B.P. 2551,CI-Bouake 1 Cote d'voire.

Fuehring, H.D., 1973. Effect of antitranspirants on yield of grain sorghum under limited irrigation Agronomy Journal, 65 : 348-351.

Nasraui, B., 1993. Role of antitranspirant films in protecting plants against fungal disease.

Annals-de- L' Institu te , national. de la Recherche, Agronomique, de, Tunisie, 66: 1-2, 125-135.

Tucker, D.J., Mansfield, T.A. 1971.A simple bioassay for detecting antitranspirant activity of naturally occurring compounds such as abscisic acid. Planta (Berl.) 98, 157-163


About Author / Additional Info:
I am currently pursuing ph.D in Plant Physiology from Banaras Hindu University