| Mature ears (without husks) of hybrid maize (Zea mays L.) Funong No.1, Zhengdan 958 and Liaodan 565 were used as material. The effect of freezing injury on germination characteristics, seed vessel characteristic and ultrastructure of scutellum in seeds were studied after treating with low temperature of 0℃,-5℃,-10℃,-15℃,-20℃,-25℃and different treatments of low temperature duration of 4 h,8 h,12 h under the different moisture content of 12～15%,15～50%,20～25%,25～30%. The main results of this study are as following:1. When the moisture content was less than 15%, within 12 hours'duration of low temperature, and the temperature was between 0℃and-25℃, then the effects of freezing injury on germination characteristics was inconspicuous, and maize seeds were out of harm's way; When the moisture content was between 15～25%, and the temperature was higher than-5℃, the seeds were injured indistinctively, as the temperature dropped to-10℃, light freezing injure occurred, when the temperature was lower than-20℃, the seeds were injured markedly, as the temperature dropped to-25℃, the seeds were injured badly; When the moisture content was higher than 20%, at the temperature of-10℃, seeds were slightly injured, at-15℃, significantly injury took place, seeds were injured very badly at-20℃, the temperature of-25℃brought deadliness freezing injury to seeds, and the injury degree was increased as the duration of freezing was protracted.2. In the period of freezing injury, the main factors which influenced the vigor of maize seeds were low temperature, water containing of seeds, low temperature duration and genotype of maize. The seeds vigor was influenced by the single-factors and their interaction effects differently, and the degree of influence ordered from high to low as follow:low temperature>low temperature×water containing of seeds×low temperature duration>low temperature×low temperature duration>low temperature×water containing of seeds> water containing of seeds×low temperature duration> water containing of seeds>low temperature duration> genotype.3. The appearance of maize seed had no remarkable change with the treatments of slight freezing injury. But when the moisture content was above 20%, at the temperature of-10℃, the seed vessel departed from the embryo and some vesicles appeared; When the temperature came down to-20℃, seeds injured badly enough, the color of embryo changed from milk white to dark gray, at this time, the embryo already had lost its vigor. Cracks could be seen by the naked eyes on the inner endosperm in the hard grain type of Funong No.1, but the seed vessel had no cracks; Under the scanning electron microscope (SEM), the lines of seed surface in normal case was clear and smooth, but after the treatment of freezing injury, the lines of seed vessel become coarse and disordered, meanwhile, the wax layer and stratum corneum were damaged.4. The normal cellular structure of scutellum in maize seed was destroyed after the treatment of freezing injury. In the treatment of-10℃and 8 h, the cell wall, plasma membrane, mitochondrion and protein body were injured in different degrees, some cells arose plasmolysis partially, the internal structure of mitochondrion became disordered and the crests were bushtailed and difficult to distinguish; Protein bodies were expanded and figured as a vacuole. In the treatment of-20℃and 8 h, ultrastructure of the plasma membrane, mitochondrion, protein bodies and all kinds of cellular organs were damaged badly. A lot of cells arose plasmolysis obviously, plasma membrane was destroyed and its function of diosmosis adjusting was lost, a part of cellular liquid osmosesed from cytoplasm and filled in the space between cell wall and plasma membrane; Lipoids almost vanished; The nuclear membranes were destroyed and disintegrated, nucleolus were highly condensed; The membrane of mitochondrion was destroyed, the quantity of crests in mitochondrion decreased, even wholly mitochondrion was disjointed; Cell wall ruptured in the case of serious freezing injury, and the organ remains osmosesed to intercellular space.
|
PDF Full Text Request