Development and cell surface of a non-syncytial invasive tapetum inCanna: Ultrastructural,freeze-substitution,cytochemical and immunofluorescence study

Summary The anther ofCanna indica L. ×C. sp. hybrid contains a hitherto uncharacterized non-syncytial, invasive category of tapetum. With the onset of prophase I the tapetal walls are dissolved and the released protoplasts migrate into the loculus, where they stay discrete. Concomitant with the dissolution of walls the tapetal protoplasts develop a 17 nm thick extracellular granulo-fibrillar cell coat. This feature develops in the synchronous phase of tapetal development. The cell coat reacts positively with ruthenium red, potassium ferrocyanide, ConA-FITC and in the Thiéry reaction. Immunofluorescence microscopy using anti-tubulin revealed that even after the migration of tapetal cells into the loculus, the microtubules retain a predominant orientation in the cell cortex, probably derived from that in the original tapetal walled cells. This order is lost during late post-meiotic stages when the cells distort and can produce amoeboid processes. The microtubule orientation is correlated with that of the cell coat fibrils. Tapetal cells vary in ultrastructure and the density of cell coat fibrils after their migration into the loculus, but the cell coat persists until the cells degenerate. It is surmised that development of the cell coat relates to the lack of cell fusion and that the cortical microtubules help to sustain cell form. During post-meiotic stages the free tapetal cells develop massive peripheral arrays of interconnected ER cisternae, probably as part of a secretory apparatus which matures when the spores are producing their ornamented walls. Buds grown in colchicine solution showed accumulation of sporopolleninlike granules in all extracellular spaces of the anther cavity.