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Macroelements necessary for plants and their functions
Nitrogen is the main component of protein. The cytoplasm, nucleus and enzyme composition of plant cells are inseparable from protein. In addition to protein, nucleic acids as genetic materials and phospholipids that form biofilms also contain nitrogen. At the same time, nitrogen is also a component of several substances with important physiological functions, such as chlorophyll involved in photosynthesis, plant hormones involved in growth and development regulation-indoleacetic acid, cytokinin and so on. It can be seen that nitrogen occupies a primary position in plant life activities and is called life element. When plants lack nitrogen, the synthesis process of nitrogen-containing substances such as protein is obviously reduced, cell division and elongation are restricted, and chlorophyll content is reduced. As a result, plants are short and thin, and their leaves are small in color. Because nitrogen can be reused in plants, young leaves absorb nitrogen from old leaves when nitrogen is lacking, so it shows that old leaves are easy to turn yellow and dry up. If there is too much nitrogen in plants, a lot of carbohydrates will be used to synthesize protein, chlorophyll and other substances, which will greatly reduce the cellulose and pectin in the cell wall. So the cells are big and thin. Vulnerable to pests and diseases. At the same time, the mechanical structure of the stem is underdeveloped and prone to lodging. Phosphorus combines with other organic substances in plants to form phospholipids, nucleic acids and coenzymes. Phospholipid is the basis of biofilm, nucleic acid is the main component of nucleus and cytoplasm, and coenzyme can participate in many important metabolic processes. So phosphorus is also an element of life. Phosphorus is closely related to nitrogen nutrition. When plants are short of phosphorus, the synthesis of protein is blocked, the formation of new cytoplasm and nucleus is reduced, which affects cell division, and the growth of plant buds and root tips is slow, resulting in small leaves, few branches and obviously short plants. But the leaves are dark green, which may be due to the slow growth of leaves and the relative increase of chlorophyll. Because phosphorus is indispensable for cell division and meristem growth, phosphorus deficiency is more obvious at seedling stage. Sulfur participates in the formation of sulfur-containing amino acids such as cystine and methionine in plants. Since most protein contains sulfur-containing amino acids, sulfur is also a component of protoplasm. At the same time, sulfur is also a participant in metabolic activities, participating in the regulation of redox process, respiration and the synthesis and transformation of some substances in cells. Therefore, sulfur plays a wide range of physiological roles in plants. When plants are deficient in sulfur, the synthesis of sulfur-containing amino acids decreases, the content of protein decreases, and the formation of chlorophyll is also affected accordingly. The symptom of sulfur deficiency in plants is yellow-green leaves. Unlike nitrogen, phosphorus and sulfur, potassium does not participate in the composition of organic matter in plants, and mainly exists in ionic state. Potassium is an activator of many enzymes in metabolism. The formation and transportation of carbohydrates in plants are inseparable from potassium; Potassium is also closely related to protein metabolism, which can promote the formation of protein. Potassium can also increase the hydration degree of protoplasm, reduce the viscosity, enhance the water retention capacity of cells and maintain a certain tension of cells. When potassium is deficient, the leaves are reddish-brown spots, the leaf edges and tips are scorched and necrotic, and sometimes the leaves curl and shrink. Potassium, like nitrogen, can be reused in plants. When potassium is deficient, young leaves can absorb potassium from old leaves. So the symptoms of potassium deficiency are first manifested in the lower old leaves. In addition, when potassium is deficient, the internodes of the stem become shorter, the stem is weak and prone to lodging. In plants, calcium can combine with pectin to produce calcium mucus, which is an indispensable component of cell wall mesothelium. When calcium is deficient, the formation of cell wall is blocked, which affects cell division, or cell division is incomplete, so that new cell wall cannot be formed, and multinucleated cells appear, which affects plant growth. Calcium and nitrogen metabolism are closely related, and nitrogen reduction needs calcium. Calcium plays an important role in the synthesis of plant protein, the transport of carbohydrates and the neutralization of organic acids. Magnesium is the basic component of chlorophyll. When magnesium is deficient, the formation of chlorophyll and the function of photosynthesis are hindered. Magnesium is also the activator of many enzymes, and there are dozens of enzymes activated by magnesium. Magnesium can also promote the combination of ribosome subunits, thus maintaining the stability of ribosome structure and ensuring the synthesis of protein. Magnesium can be reused in plants and transferred to new tissues. Therefore, when magnesium is deficient, the leaves on the lower old leaves first turn green, and then gradually die.