Journal of Experimental Botany, Vol 49, 1729-1739, Copyright © 1998 by Oxford University Press
M Pozo, C Azcon-Aguila, E Dumas-Gaudot and J Barea
New chitosanase acidic isoforms have been shown in Glomus
mosseae-colonized tomato roots and their induction, together
with the previously described mycorrhiza-related chitinase isoform, has
been further corroborated in plants colonized with another
Glomus species (G.
intraradices),as well as in tomato roots colonized in
vitro by Giaspora rosea. The induction of
these chitosanase isoforms appears as a specific response to the arbuscular
mycorrhizal (AM) symbiosis, and does not correspond to unspecific defence
mechanisms, since these isoforms were not induced by the pathogen
Phytophthora parasitica. Analysis by
isoelectrofocusing showed two closely migrating chitinase isoforms,
specific to mycorrhizal plants colonized either with G.
mosseae or G. intraradices, and their
isoelectric points were estimated to be 4.5 and 4.7. The estimated
molecular mass of chitosanases was 20 kDa, and after isoelectrofocusing,
the chitosanase activities were detected along the acidic pH range
(6.5-3.5). Constitutive and induced isoforms were also investigated during
a time-course study. In some experiments, chitin and chitosan were embedded
together as substrates in polyacrylamide gels with the aim of studying the
capacity of some isoforms to display both chitinase and chitosanase
activities. In extracts from plants colonized with either G.
mosseae or G. intraradices, some
constitutive chitinases and the previously described mycorrhiza-related
chitinase isoform, appeared to display chitosanase activity, while this
bifunctional character was not found for the chitinases from
non-mycorrhizal tissue, nor in Phytophthora-infected
plants. These results suggest some diversity in the chitinase activities
concerning substrate specificity in mycorrhizal plants. The possible
implications of these observations in the functioning of the symbiosis is
discussed.Key words: Arbuscular mycorrhizas, chitinases, chitosanases,
Phytophthora parasitica, tomato,
Lycoperiscon esculentum.
ARTICLES
Chitosanase and chitinase activities in tomato roots during interactions with arbuscular mycorrhizal fungi or Phytophthora parasitica
Departmento de Microbiologia del Suelo y Sistemas Simbioticos, Estacion Experimental del Zaidin, CSIC, 18008 Granada, Spain; Laboratoire de Phytoparasitologie INRA/CNRS, CMSE, INRA, BV 1540, 21034 Dijon Cedex, France; Corresponding author
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