Minerals enter into plants through roots. Plants were found to be consisting of more than 60 elements. Selenium and gold are also accumulated by some plants. Plants surviving near nuclear test sites will absorb even radioactive strontium. How to check whether the plant is really in need of all the minerals. How to know about the essential minerals for the plants.
Criteria for essentiality
The reasons for the elements to be considered essential for the plant growth are mentioned below.
- The normal growth and reproduction of the plant is supported and the plants depend on the elements to complete their life cycle and prepare the seeds for further propogation.
- The requirement of the element is specific and cannot be replaced by another element.
- This element is involved in the plant metabolism directly.
Based on the above mentioned features, a few elements were found to be completely essential for the plant metabolism and growth. These elements are further widely divided into two categories, like macro nutrients and micro nutrients.
These are generally present in the plant tissues in large amounts, like 10mmole per kg of dry matter. The macronutrients include oxygen, hydrogen, nitrogen, carbon, sulphur, calcium, potassium, magnesium and phosphorus. Of all these elements, carbon, oxygen and hydrogen are mainly obtained from water and carbon-di-oxide, while the other elements are taken from the soil as mineral nutrition.
These are called trace elements as they are necessary in small amounts. These nutrients include copper, manganese, iron, molybdenum, nickel, boron, chlorine and zinc.
Apart from the above mentioned nutrients, there are some more useful elements such as selenium, sodium, cobalt and silicon which are used by the higher plants. Based on the relevant functions of the essential elements, they are classified into four categories. They are:
- Essential elements that form part of the biomolecules and that are seen as structural part of the cell, like carbon, hydrogen, nitrogen and oxygen.
- Essential elements that are part of the components of the chemical substances in plants, like phosphorus in ATP and magnesium in chlorophyll.
- Essential elements that act as catalysts in activating or inhibiting the emzymes. For example, Mg2+ activates Ribulose bis-phosphate carboxylase oxygenase and phosphoenol pyruvate carboxylase, which are critical enzymes in photosynthetic carbon fixation processes. Nitrogenase is activated by molybdenum, alcohol dehydrogenase is activated by zinc during the process of nitrogen fixation. There are several other biochemical pathways that involve minerals in the process.
- Essential elements can also change the osmotic potential in the cell. Stomatal opening and closure are influenced by potassium. Minerals show impact on determining the water potential in the cell.