Maize pollen-plants of the variety Eight-Row White were obtained with anther-culture technique. Those plants were then grown to maturity and intercrossed. Microsporocytes of 19 plants from the intercrossed progeny (P2) were collected and fixed with acetoalcohol (3:1) fixative for examinations. In the meantime, microsporocytes of the controls grown from the parental plants from which the anthers were originally derived were likewise prepared for comparison. The following characteristics of the P2 plants were found:
At pachytene stage, the chromosomes were generally well-spread. All of the cells were found to have 10 bivalents. No gross aberrations, such as inversions, translocations, deficiencies and duplications were observed. However, aberrant types of nucleolus were consistently present. These aberrant types varied from cell to cell and from plant to plant. The most commonly found types were rod-shaped, crescent-shaped and bell-shaped. In addition, more than 10 percent of the cells were found to have two nucleoli instead of one. Those two nucleoli were usually unequal in size and it was most likely to have the smaller one attached to the bivalent nucleolar chromosome, and the other remained free. These binucleolar sporocytes continued their binucleolar condition throughout the first meiotic prophase. The relationship between the nucleolus and the nucleolar chromosomes was very clear at diakinesis.
At anaphase I, chromatid bridges and fragments were also observed. In certain plants, more than 10 percent of the sporocytes had these kinds of irregularity. However, as stated in the foregoing, inversions were not definitely identified at pachytene stage. It is likely that these bridges and fragments are not the products of crossing-over within the inversion loop. They are probably caused by chromosome stickiness induced by certain mechanisms developed during in vitro growth. In view of the above findings it is reasonable to say that maize anther culture in vitro and regeneration through callus can bring about variations to the newly produced plants, since no such abnormalities were found in the controls.
Y. C. Ting, Ming-kwang Ku,* Li-chuan Kuo,* Chiao-huang Hwang* and Kai-Wen Yuan*
*The Institute of Genetics, Academia Sinica, Peking, China
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