Paper Title
Male Gametophyte Development in an Endangered Plant Species Pancratium Maritimum L

Abstract
Pancratium maritimum L. (Amaryllidaceae) is an endangered plant species growing naturally in the Black Sea and the Mediterranean coasts of Turkey. In this study, pollen development in Pancratium maritimum L. was investigated from the sporogenous cell to mature pollen grain stages using transmission electron and light microscopy to understand whether the pollen development in P. maritimum follows the basic pattern in angiosperms. To follow pollen ontogeny through sequential developmental stages, anthers at different developmental stages were fixed and embedded in Epon according to the usual method. For light microscopy studies transverse sections at the thickness of 1-�m were cut using ultramicrotome and stained with toluidine blue for general histological observations. For transmission electron microscopy studies ultrathin sections (50�120 nm) were cut from the Epon embedded material and stained with uranyl acetate and lead citrate. Considerable ultrastructural changes occur in the cytoplasm of microsporocytes, microspores, and pollen grains throughout pollen ontogeny. Microsporocyte differentiation regarding number and ultrastructure of organelles facilitates the transition of microsporocytes from the sporophytic phase to the gametophytic phase. However, cytoplasmic differentiation of generative and vegetative cells supports their functional distinctness and pollen maturation. During microsporogenesis, meiocytes undergo meiosis and successive cytokinesis, leading to the formation of isobilateral, decussate and linear tetrads. After the development of free and vacuolated microspores, the first mitotic division occurs and bicellular monosulcate pollen grains are produced. Pollen grains are shed from the anther at the two-celled stage. In the course of pollen development, three periods of vacuolization were observed: in meiocytes, in mononucleate free microspores, and in the generative cell. The polarization in the distribution of organelles was observed in the early meiocytes and vacuolated microspores. Although pollen ontogeny in P. maritimum generally follows the usual angiosperm pattern, some deviations from the normal developmental pattern such as unreduced gamete formation were observed. Detailed multilateral investigations are necessary to understand whether the deviations from the normal pattern of pollen development have been developed by some members of P. maritimum as an adaptive, plastic response to the stresses of the unfavourable environmental conditions or not. Keywords- Amaryllidaceae, microsporogenesis, microgametogenesis, ultrastructure, male gametophyte