Guttation Biology



 GUTTATION 

The loss of water in the form of liquid droplets from the leaves and  other parts of an uninjured  plant is called guttation.  All plants do not show guttation . Common examples are found in Garden Nasturtium,  Oat and other cereals, Balsam, Tomato, and Cucurbits. 




 The guttated liquid is never pure water. It contains 0.6 _ 2.5 gm/ litre of solutes _ both organic and inorganic. Evaporation  of guttated liquid will leave the solutes on the surface of the leaf in term of a white crust ( another reason for the latter is excretion of salts in some halophytes). Guttation  usually  occurs  during periods of active growth when conditons favour more water absorption  and less transpiration. Such conditions are found in humid tropical areas,  rainy seasons and late spring in temperate areas. It takes place either at night or early in  the morning.  Dry soils, poorly aerated soils, heavily salted or mineral deficient soils and atmospheric conditions promoting transpiration inhibit this process. 

 Guttation drops can easily be mistaken for dew drops because  both occur in the morning.  However, dew generally  does not fall on cloudy  nights. Guttation drops are restricted to tips or margins of the leaves while dewdrops are found all over the plant and even the soil. 

  Guttation takes place through special structures called hydathodes. They are usually  found on the margins and tips of the leaves. Each hydathode consists of a group  of  loosely arranged colourless and parenchymaous cells called epithem. It lies over the tip of a vascular strand and communicates with the outside through a permanent  pore in the epidermis called water pore or water stoma. Exudation of liquid from the water pore is due to the development  of a positive pressure  in the xylem present in the vein ending. The pressure  forces the liquid out through the hydathode. The epithem cells are specialized  cells ( called transfer cells) which help in absorbing  a good  percentage of inorganic  and organic solutes present in the exudate.    A part of these solutes do come out of the hydathode along with the liquid. 




Bleeding 

It is the exudation of sap or watery solution  from the  cut or injured parts of the plant, e.g., Agave. It occurs due to root pressure,  phloem pressure,  local pressure  in xylem( stem pressure) and exudation  of latex or resin. 

Differences between Transpiration and Guttation 



Transpiration :

1) Usually  occurs  in the day.

2) Water is given out in the form of vapours. 

3) Water vapours are pure. 

4) Occurs through stomata, lenticel, or cuticle

5) It is a controlled  phenomenon. 

Guttation

1) Usually  occurs in the night.

2) Water is given out in the form of liquid.

3) Various   dissolved  substances are present in guttation  water. 

4) Occurs through hydathodes. 

5) It is unconstitutional  phenomenon. 



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