Chemistry Reference
In-Depth Information
that MeSA as well as azelaic acid and small lipids are earlier signals. As MeSA is
predicted to be very poorly phloem mobile, the mechanism of long distance
transport of this volatile compound remains to be elucidated.
Keywords Salicylic acid
Salicylic acid metabolites
Salicylic acid analogs
Cell compartmentation
Long distance transport
Ricinus model
Diffusion
predictors
1 Introduction
Salicylic acid (SA) or 2-hydroxybenzoic acid belongs to the very large group of
plant phenolics which play an essential role in plant growth, development and
interaction with other organisms (Harborne
1980
). It has been known for a long
time that SA is the natural inducer of thermogenesis in several aroid species
(Raskin et al.
1987
; Raskin
1992a
,
b
) and can be involved in the regulation of
flowering in some species, especially in combination with gibberellins (Raskin
1992a
,
b
). A new chapter in SA research started from the discovery that SA
applied to leaf tissues induces resistance to tobacco mosaic virus (TMV) in
tobacco as well as the formation of PR proteins (White
1979
).
Two decades ago, SA was classified under the group of plant hormones (Raskin
1992a
,
b
). According to the well admitted definition, a hormone is an organic
molecule that acts at very low concentrations locally and/or at distance from the
site of its synthesis. SA meets these criteria taking into account its small amounts
in plant tissues, its presence in the phloem sap and the variation of its concen-
tration in response to pathogen attack (Malamy et al.
1990
; Metraux et al.
1990
).
Since these early findings, many aspects of SA properties have been studied in
detail (see the other chapters in this topic). It can be added that SA is also highly
involved in the plant-phloem feeding insect relations (Bostock
2005
; Zarate et al.
2007
; Giordanengo et al.
2010
).
2 Transport Between Cell Compartments
Pathogen infection and abiotic stress such as UV light and ozone promote SA
accumulation. SA synthesis occurs via the phenylalanine pathway in the cytosol or
the isochorismate pathway in the chloroplast (Wildermuth et al.
2001
). SA can be
converted in the cytoplasm to several metabolites such as salicylic acid 2-O-ß-D-
glucoside (SAG), methyl salicylate (MeSA), methyl salicylate 2-O-ß-D-glucoside
(Me SAG), salicylic acid glucose ester (SGE) and dihydroxyderivatives. In most
cases, SAG appears to be the major metabolite. Like glucose conjugates of other
hormones, it is stored in the vacuole (Dean and Mills
2004
).
Search WWH ::
Custom Search