Agriculture Reference
In-Depth Information
Fig. 13.1
A dual role for vacuolar fructans in the vicinity of the tonoplast under stress? Abiotic
and biotic stresses can lead to increased concentrations of cytosolic H
2
O
2
, which can enter the
vacuole via diffusion and/or through aquaporins. Alternatively, the oxidative stress can be trans-
mitted through the action of a putative vacuolar NADPH oxidase. Vacuolar fructans can insert
deeply between the headgroups of the tonoplastic membranes, stabilizing them under stress. Type
III peroxidases (POX) associate intimately with the inner side of the tonoplast. Peroxidases also
produce
•
OH radicals. Fructans are well-positioned to scavenge these radicals, a process in which
fructan radicals and water are formed. Fructan radicals might be generated back into fructans with
the help of phenolic compounds. (see Fig.
13.2
)
the chloroplast envelope. Yet, the finding of raffinose transporters at this location
urges further research in fructan accumulating plants.
5 Sugars as Signals
Small soluble sugars (glucose, fructose, sucrose) can also act as signals. They are
now recognized as pivotal integrating regulatory molecules that control gene ex-
pression related to plant metabolism, stress resistance, growth and development
(Rolland et al.
2006
; Smeekens et al.
2010
; Cho and Yoo
2011
; Li et al.
2011
). It
is becoming increasingly clear that the hexose/sucrose ratio is an important param-
eter to adjust plant metabolism (Weber et al.
1995
; Xiang et al.
2011
). Therefore,
the interest in acid and neutral type of invertases and their inhibitors (or binding
partners) is steeply increasing (Xiang et al.
2011
; Hothorn et al.
2010
). Intrigu-
ingly, the responses to sugar signals and to oxidative stress are linked. Sugars also
affect scores of stress-responsive genes (Bolouri-Moghaddam et al.
2010
) but the
crosstalk between sugar and ROS signaling pathways needs further exploration.
