Microsporogenesis in the endangered species Cupressus dupreziana A. Camus:evidence for meiotic defects yielding unreduced and abortive pollen

To understand the reproductive biology of Cupressus dupreziana A. Camus (Cu pressaceae), a highly endangered Mediterranean conifer, the processes of mi crosporogenesis and pollen differentiation were investigated cytologically. Pre-meiotic development proved to be similar to the coniferous pattern: th e microsporangia differentiated sporogenous tissue in which microsporocytes separated and underwent meiosis. As the meiotic steps proceeded, unexpecte d irregularities were observed concerning chromosomal and nuclear behaviour . This mainly included: abnormal chromosome segregation and cytokinesis, an d nuclear fusion of the meiotic products. The result was the formation, in the same microsporangium, of heterogeneous microspore populations arranged in monads, dyads, triads, tetrads, and polyads, and cytoplasts giving rise to pollen grains of different sizes. This indicates that in C. dupreziana b oth abortive and unreduced pollen grains are generated. The significance of the finding is discussed in relation to reproductive biology and vulnerabi lity to extinction.