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Ultrastructural Observations on CTC‐Induced Callose Formation in Riella helicophylla
Author(s) -
Lerchl Daniela,
Hillmer Stefan,
Grotha R.,
Robinson D. G.
Publication year - 1989
Publication title -
botanica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 0932-8629
DOI - 10.1111/j.1438-8677.1989.tb00068.x
Subject(s) - vesicle , callose , ultrastructure , biophysics , fluorescence microscope , chemistry , cytoplasm , electron microscope , negative stain , endoplasmic reticulum , membrane , cell wall , fluorescence , biology , anatomy , biochemistry , physics , quantum mechanics , optics
The Ca 2+ ‐chelator CTC binds to a specific site on both outer surfaces of all non‐meristematic cells of the unistratose thallus of Riella , known to be rich in anionic wall components and calcium, and induces there the deposition of callose. Structural changes in this region during prolonged CTC treatment have been followed by light and transmission electron microscopy. With fluorescence microscopy punctate structures can be detected after 10 min, which upon longer incubation in CTC develop into large vesicular bodies, surrounded by a circular structure. The aniline blue‐derived fluorescence intensity of these structures is highest in cells of the extension growth zone. At the ultrastructural level a mosaic of numerous smooth‐surfaced vesicles, presumably containing callose, initially appears subjacent to the plasma membrane. These vesicles swell and fuse with each other, forming ultimately a circular fusion profile with the plasma membrane. This complex of callose‐forming vesicles is thought to develop from elements of the partially coated reticulum (PCR), based on the presence of coated vesiculation profiles on the callose vesicles and numerous aggregates of coated vesicles in their immediate vicinity. After 30 min in CTC osmiophilic particles appear around these callose vesicles and at the cytoplasmic face of mitochondria. They are later (after 60 min) deposited in the periplasmic space between wall and plasma membrane and are also released into the surrounding medium. As judged by their reaction with FeCl 3 , the osmiophilic particles appear to be phenolic in nature. We propose that upon binding of CTC a local increase of cytoplasmic calcium triggers callose synthesis in PCR‐like compartments beneath the plasma membrane. However it remains to be shown as to why callose is synthesized exclusively in these intracellular compartments and not at the plasma membrane.