Solution  culture is being  used for raising  flowers and vegetables  at home. This soil less production   of plants is called hydroponic. Plants are raised in small tanks. They are filled up with a solution  containing  appropriate  quantities  of all minerals  elements. The solution  is changes from time to time. It has a mechanism  for aeration  and circulation. Iron is added  as Fe_ EDTA otherwise  it gets precipitated,  especially  in alkaline  pH.  The agent which keeps metals in the soluble state is called chelating agent or ligand. EDTA (Ethylene  diamine tetra_ acetic acid)  is one such  agent. Fe _ EDTA complex  is called chelate. Hydroponics  is useful  in areas having thin, infertile and dry soils. They conserve water. Additionally Hydroponics can regulate pH optimum for a particular  crop, control soil borne pathogens, avoid problems  of weeding  and obtain consistently  better yields. Out of season vegetables  and flowers can also be obtained. The cost of setting  up a hydroponic  system is very high. 

Methods of Study the Mineral requirements of plants: 

In 1860, Julius von Sachs, a prominent  German  botanist,  demonstrated,  for the first time, that plants could be grown to maturity in a defined  nutrient solution in complete absence of soil. This technique  of growing  plants in a nutrient  solution  is known as hydroponics. Since then, a number of improvised methods have been employed  to try and determine  the mineral nutrients  essential  for  plants. The essence of all these methods involves  the culture of plants in a soil_ free, defined mineral  solution . These methods  require purified  water and mineral nutrient salts

Can  you  explain  why  is this so  essential?

 After a series of experiments  in which the roots of the plants  were  immersed in nutrient solutions and wherein  an element  was  added/  substituted/ removed or given in varied  concentration, a mineral solution suitable  for the plant growth  was obtained. By this  methods,  essential  elements  were identified  and  their deficiency  symptoms discovered.Hydroponics has been successfully  employed  as a technique for the commercial  production of vegetables  such as tomato, seedless cucumber and lettuce. It must be emphasised that the nutrient solutions must be adequately aerated  to obtain the optimum growth. 

What would  happen if solutions were properly  aerated? 

Diagrammatic views of the hydroponic technique 

Diagram of a typical set _ up for nutrient solution culture 

Hydroponic plant production. Plants are grown in a tube or trough placed on a slight incline. A pump  circulates a nutrients solution from a nutrient  solution from a reservoir to the elevated  end of the tube. The solution  flows down the tube and returns to the reservoir due to gravity. Inset  shows a plant whose roots are continuously  bathed in aerated nutrient solution. The arrows indicates the directed of the flow.

Essential  Mineral  Elements  

Most of the minerals present  in soil can enter plants through roots. In fact more than sixty elements  of the 10t discovered  so far are found in different  plants. Some plant species  accumulate  selenium,  some others gold,  while some plants growing  near nuclear test sites take up radioactive  strontium. There are techniques  that are able to detect  the minerals even at a very low concentration  ( 10-⁸ g/ mL). The question is , whether all the diverse mineral elements  present in a plant, for example, gold and  selenium as mentioned  above, are really nece for plants? 

 How do we decide what is essential  for plants and what is not? 

Criteria for Essentially  

The criteria for essentially  of an element  are given below: 

(a) The element must be absolutely  necessary  for  supporting  normal growth and reproduction. In the absence of the elements  the plants do not  compete their life cycle or set the seeds. 

(b) The requirement  of the element must be specific  and not replaceable  by another element. In other words, deficiency  of any one element  cannot be met by supplying  some other element.

(c)   The element must be directly  involved  in the metabolism  of the plant. 
Based upon the above criteria  only a few elements  have been  found  to  be absolutely  essential for plant growth and  metablism. These  elements  are further divided into two broad categories   based on their quantitative  requirements. 

(i) Macronutrients and 

(ii) Micronutrients 

Macronutrients  are generally  present  in plant tissues  in large amounts  ( in excess of 10 mmole Kg-¹ of dry matter). The macronutrient  include carbon, hydrogen, oxygen, nitrogen, phosphorus , sulphur,  potassium,  calcium  and magnesium. Of these, carbon, hydrogen  and  oxygen are mainly  obtained from CO2 and H2O,  while the others are absorbed  from the soil as mineral nutrition. 

Micronutrients  or trace elements, are needed  is very small amounts  ( less than 10 mmole Kg-¹ of  dry matter). These include iron, manganese, copper,molybdenum,  zinc,  boron, chlorine  and nickel. 

 In addition  to the  17 essential  elements named above, there are some beneficial  elements  such as sodium,  silicon, cobalt and selenium . They are required  by higher plants. 

 Essential  elements  can also be grouped into four broad categories  on the basis of  their diverse functions.  These categories  are : 

(i)  Essential  elements  as components of biomolecules  and hence structural elements  of cells ( e.g., carbon, hydrogen,  oxygen and nitrogen). 

(ii) Essential   elements  that are components  of energy _ related  chemical  components  in plants ( e.g., magnesium  in chlorophyll  and phosphorus  in ATP).  

(iii)  Essential  elements  that activate  or inhibit enzymes , for example Mg²+is an   activator    for both ribulose  bisphosphate  catboxylase_ oxygenase and  phosphoenol pyruvate  carboxylase,  both of which are critical  enzymes  in photosynthetic  carbon fixation; Zn²+  is an activator of alcohol  dehydrogenase  and Mo of nitrogenase during  nitrogen  metabolism . Can you name a few  more elements  that fall in this category? For this, you will need to recollect  some of the biochemical  pathways  you have studied earlier.  

(iv)  Some  essential  elements  can alter the osmotic  potential  of a cell. Potassium  plays an important  role in the opening  and closing  of stomata. You may recall the role of minerals  as solutes  in  determining  the water potential  of a cell. 


Popular posts from this blog



Nucleic Acids