Leaf and root responses to iron deficiency in avocado1

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Abstract
Physiological responses to iron (Fe) deficiency were characterized in the roots and leaves of avocado plants. These responses included sharply higher catecholase activity, but slightly lower peroxidase activity in leaves and roots of avocado seedlings grown in minus Fe nutrient solutions, and in Fe‐deficient leaves of field trees. Iron deficiency in avocado seedlings resulted in much higher rates of MTT [3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide] reduction on the root surfaces. Similarly, the initial rates of FeHEDTA reduction were greater for roots of Fe‐deficient avocado seedlings. In contrast, root respiration rates were relatively unaffected by Fe deficiency. Large differences in the manganese (Mn) and zinc (Zn) concentrations in the leaves of the Fe‐deficient and Fe‐sufficient avocado seedlings suggested that the physiological responses that occurred in the roots during Fe deficiency influenced the uptake of other metal micronutrients.