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Calcium element and Calcium Nutrition

Author : Doctor Liu Date : 8/10/2011 12:16:21 AM
Calcium has several distinct functions within higher plants. Bangerth (3) suggested that these functions can be divided into four main areas: (a) effects on membranes, (b) effects on enzymes, (c) effects on cell walls, and (d) interactions of calcium with phytohormones, although the effects on enzymes and the interactions with phytohormones may be the same activity. As a divalent ion, calcium is not only able to form intramolecular complexes, but it is also able to link molecules in intermolecular complexes (4), which seems to be crucial to its function. 

SYMPTOMS OF DEFICIENCY AND EXCESS
Plants deficient in calcium typically have upper parts of the shoot that are yellow-green and lower parts that are dark green . Given the abundance of calcium in soil, such a condition is unusual, although it can arise from incorrect formulation of fertilizers or nutrient solutions.

However, despite the abundance of calcium, plants suffer from a range of calcium-deficiency disorders that affect tissues or organs that are naturally low in calcium. These include blossomend rot (BER) of tomato pepper (Capsicum annuum L.), and water melon (Cucumis melo L.) fruits, bitter pit of apple (Malus pumila Mill.), black heart of celery (Apium graveolens L.), internal rust spot in potato tubers and carrot (Daucus carota L.) roots, internal browning of Brussels sprouts (Brassica oleracea L.), internal browning of pineapple (Ananas comosus Merr.), and tip burn of lettuce (Lactuca sativa L.) and strawberries (Fragaria x ananassa Duch.) Recently, it has been suggested that the disorder ‘crease’ in navel and Valencia oranges (Citrus aurantium L.) may be caused by calcium deficiency in the albedo tissue of the rind . 

In these disorders, the shortage of calcium in the tissues causes a general collapse of membrane and cell wall structure, allowing leakage of phenolic precursors into the cytoplasm. Oxidation of polyphenols within the affected tissues gives rise to melanin compounds and necrosis . With the general breakdown of cell walls and membranes, microbial infection is frequently a secondary effect. In the case of crease, calcium deficiency may give less adhesion between the cells of the rind, as the middle lamella of these cells is composed largely of calcium salts of pectic acid .
Local excess of calcium in the fruit gives rise to goldspot in tomatoes, a disorder that mostly occurs late in the season and that is pronounced with high temperature .