Agriculture Reference
In-Depth Information
2.2 Abiotic Threats and Their Connection with ROS
Often, plants are challenged with different types of stresses at the same time. Such
combined stresses can cause severe harm or decrease a plant's ability to resist con-
sequential stresses (Tester and Bacic
2005
). For example, low water supply is often
accompanied by high temperature stress, high photon irradiance and soil mineral
toxicities constraining root growth (Tester and Bacic
2005
). More severe drought
stresses can make a plant more susceptible to damage from high irradiance (Tester
and Basic
2005
). Another example is chilling stress going along with water defi-
cits by disturbed water transport, leading to ROS accumulation and damage to cell
membranes (Hodges et al.
1997
; Kawakami et al.
2008
). In fact, the first harmful
effects in case of hypothermia in cold-tolerant and, especially, cold-sensitive plants
are caused by increased oxidative stress. The generation of the superoxide radical
seems to occur in an initial step (Sinkevich et al.
2010
).
Other stress conditions also lead to increased ROS production, such as high pho-
tosynthetic activity in source leaves leading to temporal sugar accumulation. How-
ever, these sugars are believed to counteract (directly or indirectly) oxidative stress,
perhaps contributing to re-establishing cellular ROS homeostasis (see below). Sug-
ar starvation too can lead to ROS accumulation (Bolouri-Moghaddam et al.
2010
).
Taken together, both sugar shortage and excesses might lead to a disturbance of
respiratory metabolism, leading to excess ROS during mitochondrial electron trans-
port (Xiang et al.
2011
). In rice, cytoplasmic male sterility (CMS) was found to be
correlated with ROS overproduction and ATP depletion, leading to mitochondrial
failure and disturbance of pollen development (Nguyen et al.
2010
).
3 Stress-Related Carbohydrates and Their Metabolism
Some soluble carbohydrates (glucose, fructose and sucrose) in concert with hor-
mone-signaling pathways are crucial in signaling events controlling plant growth
and development (Smeekens et al.
2010
; see also below). There are three main
water-soluble carbohydrate types (collectively referred to as “sugars” from this
point on) that play essential roles in plant stress responses: disaccharides (sucrose,
trehalose), RFOs and fructans. Typically, such sugars can accumulate under (mild)
stresses when growth is restricted but photosynthesis is not (or only partially) inhib-
ited (De Roover et al.
2000
; Muller et al.
2011
; Skirycz et al.
2011
).
3.1 Disaccharides
Sucrose (Glcα(alfa)1,2β(beta)Fru) is one of the most widespread disaccharides in
nature (Salerno and Curatti
2003
). In higher plants, it represents the major transport
compound bringing carbon skeletons from source (photosynthetically active leaves)
to sink tissues (roots, young leaves, flowers, seeds, etc.)(Koch
2004
). Although
