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revealed that fl g22 induced a rapid (about 2 min) response, usually with two or three
minor, decreasing peaks, whereas elf18-induced calcium infl ux pattern was less
defi ned and broader (Aslam et al.
2009
).
The PAMPs xylanase and the HAMP OGs activate AtMPK6 with characteristic
time courses in
Arabidopsis
. The OGs elicited a rapid and transient activation of
AtMPK6, with a maximal activity around 3.5 min and a nearly complete return to
basal activity after 15 min. The PAMP xylanase induced AtMPK6 activity slowly
with a maximum at 20 min. The activity decreased slowly thereafter and did not
reach the basal level within 40 min (Nühse et al.
2000
). The PAMPs fl g22 and chitin
also behaved differently in activating AtMPK6 in different time courses (Nühse
et al.
2000
). OG induced AtMPK3 activity within 3 min of exposure to the HAMP,
and the enzyme activity returned to basal levels by 10 min. In contrast, AtMPK3
activity induced by fl g22, was strong at 3 min, and was still robust at 10 min following
elicitation (Denoux et al.
2008
).
Different elicitors may induce the same signaling system, but the intensity of
gene expression may differ. The proteinaceous elicitors (elicitins and harpin)
induced a pronounced and sustainable [Ca
2+
]
nuc
elevation, relative to the small
effects of oligosaccharide elicitors (oligogalacturonides and
-1,3-glucan)
(Lecourieux et al.
2005
). Both cryptogein and OGs, the two different elicitors, trig-
gered Ca
2+
infl ux in
Nicotiana plumbaginifolia
cells, but the two [Ca
2+
]
cyt
calcium
signatures differed in both kinetics (lag time, peak time, and duration) and peak
intensities (Lecourieux et al.
2002
).
Various oligosaccharide elicitors (the PAMP
β
-1,3-glucan and the HAMPs oligo-
galacturonides [OGs] and cellodextrins [CDs]) induced transient increases in cyto-
solic calcium ion ([Ca
2+
]
cyt
) in grapevine cells almost immediately after treatment
(Aziz et al.
2007
). When the cells were treated with CD, a rapid and transient
increase of [Ca
2+
]
cyt
was observed within 1 min and peaked at 0.6 uM after 2.5 min
and decreased to 0.32 uM after 8 min. Cytosolic Ca
2+
was then maintained at this
level for about 4 min, and then decreased slowly to the background level. The Ca
2+
signature was different in peak time or intensity after treatment with the other two
oligosaccharide elicitors, OGA and
β
-1,3-glucan (Aziz et al.
2007
).
Both fl g22 and chitosan induced callose deposition in
Arabidopsis
, but both
responses showed differences in timing (Luna et al.
2011
). Furthermore, fl g22- and
chitosan-induced callose differed in the requirement for the NADPH oxidase
RBOHD, the glucosinolate regulatory enzymes VTC1 and PEN2, and the callose
synthase PMR4 (Luna et al.
2011
).
β
2.23
PAMPs May Differ in Eliciting Various Defense
Responses
Peptidoglycan (PGN), fl agellin, and chitin induced largely overlapping early signal-
ing patterns. However, defense responses induced by them were not identical. PGN
treatment resulted for instance in camalexin production whereas application of
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