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Aluminum Exclusion Mechanism in Root Tips of Maize ( Zea mays L.): Lysigeny of Aluminum Hyperaccumulator Cells
Author(s) -
Vázquez M. D.
Publication year - 2002
Publication title -
plant biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 1435-8603
DOI - 10.1055/s-2002-25736
Subject(s) - vacuole , biology , apoplast , ultrastructure , callose , cell wall , botany , zea mays , cytoplasm , xylem , cytochemistry , biophysics , biochemistry , agronomy
Ultrastructural studies, together with X‐ray microanalytical, immunocytochemical and cytochemical analysis performed in root tips of Al‐resistant (C‐525 M) and Al‐sensitive (Adour 250, HS 7777 and BR 201 F) maize plants ( Zea mays L.), after 96 h exposure to 20 μM Al, showed qualitatively similar results in the four cultivars. Al was identified in electron‐opaque precipitates, which were insoluble even in EDTA chelate. They also contained an elevated proportion of P and also of K and Ca, some traces of Mn, Fe and Zn and sometimes of Mg. This elemental composition is similar to that described for phytin (Al‐phytin), and the precipitates were localized in the two principal extraplasmatic compartments: cell walls and vacuoles. Al‐phytin was detected in swollen areas of cell walls in membraneous concentric configurations, resembling myelin figures, probably rich in phosphatidyl inositol, which also intervene in the vacuolar internalization of Al‐phytin and are similar to a peculiar form of endocytosis (not previously described). Abnormal apoplastic protuberances containing abundant electron‐opaque Al‐phytin deposits, agglutinated by callose (immunocytochemically identified), were shown in cortex cells with high mitotic activity (around 1 ‐ 1.5 mm from cap root). Al‐hyperaccumulator cells parallel to the root axis were correlated with longitudinal lysigenous intercellular spaces after cell death and dissolution (lysigeny). Indicators of activated lysigeny, as low levels of Al and callose (in agreement with other authors) and high levels of phosphoinositides, can mark Al‐resistant genotypes, contrary to Al‐sensitive genotypes, probably derived from a partially activated or even inactivated lysigeny. The lysigeny of Al hyperaccumulator cells constitutes new ultrastructural evidence of an Al exclusion mechanism, supporting biochemical results reported by other investigators.