Effect of low iron stress on root growth and iron uptake and utilization of different maize cultivars at seedling stage

Iron, as a mineral element necessary for plant growth, has a significant effect on chlorophyll synthesis, REDOX reaction, plant photosynthesis, respiration, and substance/energy metabolism. Low content of effective iron in soil can easily cause iron deficiency (chlorosis) in maize planted in calcareous soils of arid/semi-arid regions. The study of the ability/mechanism of maize to resist low iron stress is critical for solving chlorosis due to iron deficiency. In order to determine the mechanism of resistant maize cultivars to low iron stress at seedling stage, 'Zhenghong 2' (resistant to low iron) and 'Chuandan 418' (sensitive to low iron) were selected for the study. For genetic improvement of the maize varieties resistant to low iron stress, three-leaf maize seedlings were treated with different levels of iron solution with severe (10 μmol·L^-1), medium (30 μmol·L^-1), light (50 μmol·L^-1) iron stress and control (100 μmol·L^-1). Analysis of low iron stress for different maize varieties to low iron showed that the low iron stress had significant effects on root growth and iron uptake of maize seedlings after 14 and 28 days of treatments. As iron concentration decreased, root length, root volume, root vitality, dry matter, iron content, iron accumulation and relative absorption capacity of maize seedlings significantly dropped. However, iron treatment increased root-washing mugineic acid, iron distribution in aboveground parts and iron physiological efficiency of the seedlings. This was one of the most important physiological mechanisms of maize adaptation to low iron stress. Although iron accumulation had significant positive correlation with iron absorption ability of maize, iron absorption capacity under moderate and severe low iron stress in maize cultivars with different low iron resistances were not significant. Thus the difference in iron absorption ability was not the main cause of high iron accumulation in 'Zhenghong 2'. Iron accumulation was also significantly positively correlated with root length, root volume, root dry weight and root activity. Compared with 'Chuandan 418' low iron resistant variety 'Zhenghong 2' had longer root length, larger root volume, heavier root dry weight, higher root vitality and higher iron accumulation. There was a positive correlation between mugineic acid and iron distribution in stems and leaves of maize seedlings. Also a positive correlation was observed between iron physiology efficiency and iron distribution in stems and leaves of maize seedlings. The enhancement of root secretion of mugineic acid improved iron allocation rate in the shoot system of maize so as to improve the efficiency of iron physiology. The rate of increase in mugineic acid was higher for 'Zhenghong 2' under moderate and severe low iron stress and that was the main reason for the high iron physiological efficiency.