Utilization and Redistribution of Zn During Vegetative Growth of Corn

Slight changes in availability of soil Zn during the growing season may terminate or initiate Zn stress in plants. For example, under field conditions, visual symptoms of Zn deficiency may disappear after a few weeks, and grain yields of corn (Zea mays L.) may be normal. To determine the degree of recovery of young corn plants after termination of Zn stress and the effectiveness of Zn redistribution during stress, plants were grown in greenhouse sand cultures to anthesis. Levels of Zn ranged from none to 0.1 μg/ml of nutrient solution; Zn supplies were either: (a) withheld until plants had developed to the 4 or 8-leaf stage; (b) withheld after plants had developed to these stages; or (c) supplied continuously until plants were harvested at the 4, 6, 8-leaf, or anthesis stages. Leaf area, CO₂ assimilation, Zn accumulation, and dry matter yields were determined. Rates of CO₂ assimilation (mg/dm²/hour) were decreased to 72% and 10% of the rates in control plants after Zn stress of 19 and 40 days, respectively. Plants stressed for Zn, however, were able to assimilate CO₂ at 80 to 90% of normal rates 19 days after Zn was added. Percent decreases in leaf area were similar to those observed for CO₂ assimilation. Reductions in both of these growth factors caused severe restrictions in early growth and development. Plants stressed for Zn until reaching the 8-leaf stage required an additional 15 days to reach anthesis and yielded 50% as much dry matter as control plants. When stressed only to the 4-leaf stage and then supplied with Zn, plant development to anthesis was delayed 4 days, and dry matter yields were 84% of those for control plants. At anthesis, distribution of Zn in plants that had been placed under stress at the 8-leaf stage indicated there was extensive mobilization and translocation of Zn to newly developing leaf and stalk tissue.