More than 60 elements have been found in plant tissues. These elements range from as common as carbon and hydrogen to those as exotic as platinum, uranium, and gold. Are all these elements essential for growth?
Carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium and magnesium are required in relatively large amounts and are called macronutrients. Iron, chlorine, copper, manganese, zinc, boron, and molybdenum are required in relatively small amounts and are called micronutrients.
Functions of essential elements.
1. Plants require different amounts of different elements. Most plants require 60 million times more hydrogen atoms than molybdenum atoms. These different requirements reflect different uses of these elements. Hydrogen is in almost all compounds in plants, while molybdenum occurs in only in few.
2. Different elements are absorbed in different forms. Calcium and iron are absorbed as cations, while phosphorus and sulfur are absorbed as anions.
3. Most elements have several functions. Potassium is involved in starch synthesis, affects protein conformation, and activates enzymes. Although the functions of essential elements are diverse, they can be grouped into four general categories:
− Essential elements can be part of structural units. Carbon, hydrogen and oxygen make up carbohydrates such as cellulose. Similarly, nitrogen as an integral part of proteins.
− Essential elements can be part of compounds involved in metabolism. Magnesium is part of chlorophyll, and phosphorus is part of ATP and nucleic acids.
− Essential elements can activate or inhibit enzymes.
Magnesium stimulates several respiratory enzymes, while calcium inhibits several enzymes. In some cases, these enzymes may be those responsible for synthesizing plant hormones.
Essential elements can alter the osmotic potential of a cell
Date: 2014-12-22; view: 702