Ultrastructural changes in the cell wall,nucleus and cytoplasm of pollen mother cells during meiotic prophase I inLycopersicon esculentum (Mill.)

Summary Throughout the premeiotic to late prophase I stages of meiosis in the anthers of tomato (Lycopersicon esculentum) extensive changes occurred in the ultrastructure of pollen mother cells (PMCs). During early prophase, the wall of each PMC developed a layered appearance and was broadened both by the widening of the middle lamella as well as by intensive deposition of microfibrils in the wall. By late prophase, however, the microfibrils adjacent to the plasmalemma dissipated. At the same time, callose was deposited between the wall and the plasmalemma. The nucleus of the PMCs also underwent changes. During early prophase, the nucleolus consisted of a linear series of three segments, with a separation of the granular and fibrillar portions. By late prophase, the nucleoli were less distinct as the nucleus was highly vacuolate. Mitochondria were initially simple with lightly stained matrix and few cristae but, during the course of prophase, they acquired a more densely-stained matrix with dilated cristae. Plastids remained relatively undifferentiated and, at late prophase, many were convoluted in appearance and constricted at intervals indicating their division. Cytoplasmic connections between adjacent PMCs were broad enough to permit the passage of organelles and were retained through to metaphase I. These cytological and wall changes appear to be a prerequisite for the subsequent development of microspores.Abbreviations PMC pollen mother cell - NOR nucleolus organizing region