Zinc is an enzymatic and activator component. It is involved in the N metabolism and photosynthesis processes. Zinc participates in the synthesis of the tryptophan amino-acid, which is a required precursor for the indole acetic acid (IAA). IAA, a plant hormone, is an essential growing and developing regulator of sprouts, leaves and fruits. Zinc is moderately mobile once is out of the xylem.
Main characteristics of Zinc:
• Enzyme activator.
• Nitrogen metabolism.
• Fundamental role in the Tryptophan's synthesis, which is the precursor amino-acid of the auxin. This hormone has a key role in the growing of the sprouts, leaves and fruits.
Zinc is often deficient in soils with high phosphate, alkaline and calcareous levels; examples are: costal and geological shell sandy soils. Highly leachable sandy acid soils and soils derived from granitic rock as parent material are also highly susceptible to Zinc deficiencies. Even though Zinc could be present, it could be immobile in soils with high organic matter, e.g. (acids) peat and clay soils with low silicon and magnesium content. High iron concentrations can have a competitive effect in the zinc availability.
Zinc effects and deficiency symptoms
Zinc is a component of various enzymes. Deficiency symptoms are expressed in the respiration, photosynthesis and protein synthesis alteration. Also, because the production failure of the auxine growing hormone.
This causes dwarfism growing type mainly on fruit crops: short internodes (rosette) and small leaves (sick small leaves). Zinc has a key role in the pigment formation, which has a critical effect on the fruit coloring.
In maize, the Zinc deficiency appears as strips and yellow whitish spots. The necrotic symptoms are difficult to be distinguished from Fe and Mn deficiencies. It is possible a Cu and Fe competition in the Zinc complex, while in the leaves Ca, Mg and Cu are antagonism.
Most frequent zinc deficiency symptoms Zinc:
• Symptoms appear in the young leaves since Zinc cannot be mobilized from the old to the young tissues.
• Dwarfism: short internodes (rosette) and small leaves ("small sick leaves").
• In maize and rice yellow-whitish strips can occur from the lower part of the leaves. Twigs dies and the fruit quality and quantity are reduced.
• Chlorosis symptoms are similar to Mn and Fe deficiencies, and can present necrosis in the final stage.