Objectives Zn deficiency is a common limiting factor for crop growth and grain quality. Typical Zn deficiency symptoms are expressed as leaf chlorosis and necrosis. We tried to reveal whether Zn deficient causes the display of morphological and biochemical features of cell apoptosis in maize leaves.
Methods Maize cultivars Nongda 108 and Zhengdan 958 were chosen as the tested crops to carry out a hydroponic culture experiment. The Zn concentration in the nutrient solution was set up as 0 and 1.0 µmol/L, to represent Zn deficient and normal Zn supply. At 5, 10, 15 and 20 days of treatment, the seedlings were harvested for the determination of growth, biomass, and Zn content; the leaf tissue and cell microstructure were observed under optical microscopy and electronic microscopy, and the DNA ladder in leaves was measured by agarose gel electrophoresis. The DNA degradation characteristics of leaf cells were determined with DAPI (4', 6-diamidino-2-phenylindole) staining technique; the enzyme activity of caspase-3 was determined by the kit.
Results Zn deficiency significantly decreased shoot dry matter weight and Zn concentration. Under Zn deficiency, leaf cells shrined, cell spaces became narrow and irregularity were visible; the membrane of leaf mesophyll cell nucleus wrinkled, chromatin dispersed toward the edge of nuclear membrane and condensed peripherally; the nuclear structure of the bundle sheath cells deformed and shriveled, showing a irregular shape. The images of DAPI fluorescent staining also showed irregular leaf cell nuclei structure and increased nuclear fragmentations under Zn deficiency. The “DNA ladder” in leaf Zn deficient cells were visualized in bands of agarose gel electrophoresis, revealing the DNA breakdown in Zn deficient leaves. Zn deficiency induced the increase of caspase-3 activity in Nongda 108 leaves at 20 days and in Zhengdan 958 leaves at 15 days of Zn deficient treatment.
Conclusions Zn deficiency could induce the maize leaf cells to apoptosis.
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