A CASE OF MALE STERILITY IN THE ENDANGERED ENDEMIC SPECIES PITCAIRNIA ENCHOLIRIOIDES L.B.SM. (BROMELIACEAE) OF BRAZILIAN ATLANTIC FOREST INSELBERGS.

Premise of research. The endangered Pitcairnia encholirioides has limited flowering, a low rate of seed germination, and dominant asexual reproduction. These limitations suggest restrictions in sexual reproduction that could be caused by structural changes during development. Previous results indicated normal development of ovules and female gametophytes. Therefore, to test this hypothesis, anther wall development as well as microsporogenesis and microgametogenesis were analyzed. Methodology. Using cytogenetic and anatomical analysis, the study was undertaken to determine any cellular changes that might affect sexual reproduction of the species. Accordingly, we looked for (1) the presence of cytological changes during the development of anthers and pollen grains and/or (2) any cytogenetic aberration associated with meiosis of the sporogenous cells. Pivotal results. In the samples studied, anther wall development followed the monocotyledonous type, with late proliferation of the middle layer and secretory tapetum. After the establishment of these layers, most anthers showed cytological changes that led to sterile pollen grains. In those anthers that showed fertile development, a thick callose deposition was evident. Then, after dissolution of the callose and release of microspores, the tapetum began to degenerate. However, in sterile anthers, callose deposition was thin, and tapetum degeneration--which began from the establishment of microspore mother cells--was premature. Both of these conditions contributed to the formation of anomalous microspores that did not undergo gametogenesis but did undergo maturation of the pollen wall. In spite of these observations, cytogenetic analyses revealed regular meiosis in both fertile and sterile anthers. Conclusions. Pitcairnia encholirioides bears both sterile and fertile anthers at anthesis, depending on the timing of tapetum degeneration and callose dissolution. Consequently, male sterility could account for the restrictions in sexual reproduction caused by the structural changes noted above. [ABSTRACT FROM AUTHOR]