Tryptophan and Indole Acetic and Synthesis

Content

Early Research on Zinc Nutrition of Crops
Absorption and Function of Zinc in Plants
Zinc Deficiency
Zinc Tolerance
Trunk Injection
Zinc in Soils
Phosphorus–Zinc Interactions
Tryptophan and Indole Acetic and Synthesis
Root Uptake
Foliar Absorption
  Influence of Humidity on Foliar Absorption
Role of Zinc in DNA and RNA Metabolism and Protein Synthesis
Zinc Transporters and Zinc Efficiency
Summary
References

The most distinct zinc deficiency symptoms are ‘little leaf’ and ‘rosette’ in pecans and peaches (Figure 15.1 and Figure 15.2). These symptoms have long been considered to represent problems in indole acetic acid (IAA, auxin) metabolism. However, the mode of action of zinc in auxin metabolism is unidentified. Retarded stem elongation in zinc-deficient tomato (Lycopersicon esculentum Mill.) plants was correlated with a decrease in IAA level, but resumption of stem elongation and IAA content occur after zinc is resupplied. Increased IAA levels preceded elongation growth upon resupply of zinc (54), which would be expected if growth was a response of increased supply of auxin caused by application of zinc. Low levels of IAA in zinc-deficient plants are probably the results of inhibited synthesis of IAA (55). There is an increase in tryptophan content in the dry matter of rice (Oryza sativa L.) grains by zinc fertilization of plants grown in calcareous soil (56). The lower IAA content in zinc-deficient leaves may be due to the biosynthesis of IAA tryptophan (57). Lower IAA contents may be the result of enhanced oxidative degradation of IAA caused by superoxide generation enhanced under conditions of zinc deficiency (55).