TIMING OF MORPHOLOGICAL AND HISTOLOGICAL DEVELOPMENT IN PREMEIOTIC ANTHERS OF NICOTIANA-TABACUM CV XANTHI (SOLANACEAE)

The tobacco stamen has been the object of many developmental studies, and the organ has more recently become a model for molecular genetic s tudies of anther differentiation. However, the spatial and temporal de tails of cellular differentiation of early anther development have nev er been thoroughly characterized. In the present study, the age of 15 tobacco flowers from plants grown under constant light and temperature was estimated using growth analysis. Prior to tissue fixation for lig ht microscopy, moulds of stamen and anther primordia were made with a dental impression polymer so morphological and histological observatio ns could be made on each tissue sample. Flower ages spanned an 8-d int erval during which petal and stamen initiation occurred, and sporogeno us cells reached the leptonema stage of meiosis. The initial developme nt of the tetrasporangiate anther shape largely preceded periclinal di vision of archesporid initials. Anatomically, periclinal divisions in the hypodermal (I-2) layer were observed before archesporial initials began to divide. These data indicate differences in the cellular basis of tobacco anther development compared to earlier clonal analyses of Datura. The pattern of mitotic cell division associated with microspor angial development suggested modal peaks in division over time. The ab ility to estimate developmental time in the tobacco anther has implica tions for future studies directed at understanding mechanisms of anthe r evolution via heterochrony.