The tpd1 (from tobacco pollen development 1) insertion mutant of tobacco (Nicotiana tabacum L., cv. Samsun) with extended flowering period was investigated in detail in the course of plant development, and the inheritance of the mutant phenotype was established. The wild-type and mutant plants did not differ in basic developmental indices until the floral transition; later they diverged in the characteristics of male reproductive organs, particularly in anther development and pollen maturation. The pollen of tpd1 plants was underdeveloped and sterile, resulting in a characteristic seedless phenotype with extended flowering period. When mutant flowers were pollinated with wild-type pollen, the tpd1 phenotype was maintained in at least two seed generations, indicating that this trait was heritable. The tpd1 phenotype was closely linked with kanamycin resistance; it follows that the developmental anomalies observed in our experiments immediately depended on the vector DNA insert. Our data presume that tpd1 is a rare dominant monogenic mutation with a narrowly directed physiological manifestation. A model is presented to describe the effect of TPD1. The tpd1 mutant would help identify and clone the new TPD1 gene crucial for viable pollen development.
