Studies on iron chlorosis in apple plants II. The influence of iron stress on the morphological, physiological and biochemical changes in apple

The physiological and biochemical changes in chlorotic apple plants are described. The ultrastructure abnormalities in the mesophyll cell chloroplasts are correlated with the severity of symptom expression. It is likely that deficiency iron exerts its damaging effect through a number of impaired reactions of ferredoxin production and cytochrome formation. Thus photosythesis, respiration and nitrogen metabolism can not proceed properly and synthesis of macromolecules is inhibited. The reducing capacity and respiration rate increase in roots, while respiration rate decreased in leaves of iron stressed plants. The mechanism of iron reduction by apple roots seems that this reduction take place on the plasma membrane of root cells without involvement of enzymes. Screening of iron-efficiency genotype shows that the reducing capacity of apple roots is much lower than that of soybean, sunflower and cucumber, So far no iron efficiency genotype has been reported.