RECENT TRENDS IN TAPETUM RESEARCH - A CYTOLOGICAL AND METHODOLOGICAL REVIEW

Cytological, developmental, and functional aspects of tapetum cells ha ve been extensively studied in the past using classical light- and ele ctron microscopy (LM, EM). Recently, some advanced preparation methods and analytical techniques have come of age; they already have been ap plied with some success for the investigation of pollen and tapetum de velopment. Analytical transmission EM techniques (ESI, EELS) as well a s immunocytochemistry and fluorescence microscopy have become invaluab le tools for the localization of substances. Laser scanning microscopy and video-enhanced microscopy have brought about a revival of LM, the latter method permitting the study of dynamic cellular processes with high spatial and temporal resolution. Hence, so far static notions of cellular ultrastructure based on the interpretation of classical TEM micrographs can now be completed by a more dynamic concept. In TEM, th e application of freeze fixation and freeze substitution as well as so phisticated chemical fixation protocols have considerably improved ult rastructure preservation thereby revealing, for instance, that tapetum senescence starts much later than generally assumed. Some patterns of cytoplasmic disorganization which are usually interpreted as tapetum degeneration were found to result from specimen preparation. Besides p resenting recent advances in the fields mentioned above, this paper al so reviews literature on aspects of primary/secondary tapetum metaboli sms and the regulation of normal/abnormal tapetum (and microspore) dev elopment.