Exogenous Hemin Optimized Maize Leaf Photosynthesis, Root Development, Grain Filling, and Resource Utilization on Alleviating Cadmium Stress Under Field Condition

The purpose of this study was to analyze the response and mitigation mechanism of hemin to maize under cadmium stress. Maize variety Xianyu 335 was exposed to cadmium stress (100 mg kg −1 ) and was sprayed different concentrations of hemin (150, 250, and 300 μmol L −1 ) at the flowering stage. The photosynthetic characteristics, leaf senescence characteristics, root activity, bleeding, and other parameters were determined by analyzing the maize leaves and roots at 10, 20, 30, 40, and 50 days after flowering. Hemin enhanced the chlorophyll content and net photosynthetic rate of leaves; delayed leaf senescence; improved the accumulation and distribution of photosynthetic products; optimized the parameters of maize root growth characteristics, root activity, and bleeding rate; and optimized the mineral elements and amino acid contents in root bleeding under cadmium stress in field. Furthermore, hemin improved the starch characteristics of maize grain filling, promoted the activity and gene expression of key enzymes in starch synthesis, and increased maize yield and the radiation, heat, and water use efficiency of plants, which realized the synergistic improvement of maize yield and efficiency under cadmium stress. Hemin promoted the growth and development of maize leaves and roots under cadmium stress in field. The maize yield and radiation, heat, and water use efficiency were also improved synergistically, which provided technical methods for the maize production of stress resistance.