8/10/2019 CRP 101 Lecture No. 6

1/16

TRANSPIRATION - TYPES -STEWARDS Theory of Mechanism Significance

and Factors Affecting TRANSPIRATION andGUTTATION ANTITRANSPIRANTS

Dr. T. Sivakumar, Asst. Professor (Crop Physiology)

Lecture No: 6

8/10/2019 CRP 101 Lecture No. 6

2/16

Introductory DefinitionTRANSPIRATION :Loss of water (either excess

or mandatory) from the aerial parts of plants inthe form of water vapours though stomata.

GUTTATION :Loss of water (either excess ormandatory) from the aerial parts of plants in theform of water droplets through hydathode.

1. Thermoregulation2. Water and Nutrient conduction

8/10/2019 CRP 101 Lecture No. 6

3/16

Types

1. Stomatal transpiration - Its contribution is 85 - 90%of the total transpiration

2. Cuticular transpiration - Its contribution is 10% of the

total transpiration.

3. Lenticular transpiration - lost by woody stemslenticels.

8/10/2019 CRP 101 Lecture No. 6

4/16

1. Stomatal transpirationMost of the transpiration takes place through this.

More numbers of stomata are confined in the lower sides of the leaves.In monocots (e.g.. Grasses), they are equally distributed on both sides.In aquatic plants with floating leaves, they are present on the upper surface.

8/10/2019 CRP 101 Lecture No. 6

5/16

2. Cuticular transpirationCuticle is impervious to water, even though, some water

may be lost through it. It may contribute a maximum ofabout 10% of the total transpiration.

8/10/2019 CRP 101 Lecture No. 6

6/16

3. Lenticular transpirationSome water may be lost by woody stems through lenticels which iscalled as lenticular transpiration.

8/10/2019 CRP 101 Lecture No. 6

7/16

Mechanism of stomatal transpiration

It can be studied in 3 steps.Osmotic diffusion of water in the leaf from

xylem to intercellular space above thestomata through the mesophyll cells.

Opening and closing of stomata (stomatalmovement)

Simple diffusion of water vapours fromintercellular spaces to other atmospherethrough stomata.

8/10/2019 CRP 101 Lecture No. 6

8/16

Significance of Transpiration Plants waste much of their energy in absorbing

large quantities of water and most of which isultimately lost through transpiration i.e.Transpiration as advantageous to plant if it isinvolved in Thermoregulation and Water andNutrient conduction .

Otherwise it is an unavoidable process whichis rather harmful.

8/10/2019 CRP 101 Lecture No. 6

9/16

Advantages of transpiration

1. Helped in upward movement of water from rootto shoot i.e. Ascent of sap.

2. Helped in absorption of water and translocationof mineral salts for the plants from soil throughxylem elements

3. Helped in temperature regulation by way ofdissipating excess heat energy produced bythe leaves after photosynthesis; and thusprevents them from excessive heating.

8/10/2019 CRP 101 Lecture No. 6

10/16

Factors affecting transpiration Internal

1. Internal water conditions

2. Structural features

External1. Atmospheric humidity

2. Temperature

3. Wind4. Light

5. Available soil water

6. CO2

8/10/2019 CRP 101 Lecture No. 6

11/16

A. External factors1. Atmospheric relative humidity (RH) is inversely related because

atmosphere is more saturated with moisture when relative humidity ishigh and retards the diffusion of water vapour from the intercellular

spaces of the leaves to the outer atmosphere through stomata.In dry atmosphere, the RH is low and the air is not saturated withmoisture and hence, the rate of transpiration increases.

2. Temperature is directly related by lowering the relative humidity andOpening of stomata widely

3. Winds normal speed is directly related by facilitating the diffusion ofwaster vapour from the intercellular spaces of the leaves to the outeratmosphere though stomata.When the wind is blowing violently , the rate of transpirationdecreased because it creates hindrance in the outward diffusion of watervapours from the transpiring part and it may also close the stomata.

4. Light is directly related because of opening of stomata and raising oftemperature. Where as in dark, stomata will close and transpiration isalmost stopped.

5. Available soil water is directly related 6. CO 2 inversely related An increase in CO 2 concentration in the

atmosphere (Over the usual concentration) more so inside the leaf,leads towards stomatal closure and hence it retards transpiration .

8/10/2019 CRP 101 Lecture No. 6

12/16

B. Internal factors1. Internal water conditions

Deficiency of internal water due to less or nilabsorption of water by the plants will resultin decrease of transpiration rate.

2. Structural features

The number, size, position and themovement of stomata affect rate oftranspiration. E.g. In dark stomata areclosed and stomatal transpiration ischecked.

Sunken stomata help in reducing therate of stomatal transpiration. In xerophytes,the leave size is reduced or may even fall tocheck transpiration in addition to thick

cuticle.

8/10/2019 CRP 101 Lecture No. 6

13/16

Antitranspirants A number of substances are applied to retard their

transpiration in the plants. Such substances are calledas antitranspirants .

E.g. colourless plastics, silicone, oils, low viscositywaxes, phenyl mercuric acetate (PMA), abscisic acid(ABA), CO 2, etc.

Mechanism : Colourless plastic, silicone oils and lowviscosity waxes belong to one group as these are

sprayed on the leaves to form film which is permeableto O2 and CO 2 but not to water where as ABA andFungicide (PMA) at low concentration (10 -4m) or a littlerise in CO2 concentration from the natural 0.03% to0.05% induces partial closure of stomatal pores for a

period of two weeks.

8/10/2019 CRP 101 Lecture No. 6

14/16

GUTTATION In some plants, water drops ooze out from the

uninjured margins of the leaves through thespecial types of stomata called water stomata orhydathodes at the margins where a main veinends.

Below this there is a small cavity followed byepithem. Under high root pressure the water isgiven to the epithem then it is released into thecavity.

When this cavity is completely filled with waterysolution, the later begins to ooze out in the form ofwatery drops through the water pore

E.g. Garden nasturtium, tomato, colocasia etc

It takes place usually early in the morning due tohigh absorption and root pressure and very lowtranspiration.

8/10/2019 CRP 101 Lecture No. 6

15/16

Difference

Transpiration Guttation 1. Water is lost from aerial parts of

plants in the form of invisiblewater vapours

Watery solution oozes out fromuninjured margins of aerial leavesonly

2. Transpiration occurs mostlythrough stomata. It may alsotakes place through cuticle andlenticels

It occurs only through hydathodes(water stomata)

3. It takes place throughout the day,

its rate being maximum at noon.

It takes place only early in the

morning when root pressure and therate of water absorption are higher

8/10/2019 CRP 101 Lecture No. 6

16/16

You are not responsible for whatpeople think about U.

But, U are responsible for what U

give them to think about U.