Legume-rhizobia symbiotic performance under abiotic stresses: factors influencing tolerance behaviour - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 125

ChApter 8

Legume-rhizobia symbiotic performance
under abiotic stresses: Factors influencing
tolerance behaviour

Haythem Mhadhbi 1 , Photini V. Mylona 2 and Alexios N. Polidoros 3
1 Laboratory of Legumes, Centre of Biotechnology of Borj Cedria, Hammam lif, Tunisia
2 Agricultural Research Center of Northern Greece, Thermi, Greece
3 Department of Genetics and Plant Breeding, School of Agriculture, Aristotle University of Thessaloniki, Greece

8.1 Introduction 8.2 Symbiotic association:

A specific plant-microbe interaction

Leguminous plants (family Fabaceae) represent one of
the most important food, feed and forage resources. In
many developing countries, legumes are the single
most important source of proteins (Roe & Kupfer,
2004). About 33% of human nutritional requirements
for nitrogen come from legumes. They also play a
central role in the enhancement of the natural envi-
ronment since they can be fed to animals, as well as
protecting the soil, stabilizing dunes and representing
a source of medicinal products (Graham & Vance
2003). Due to the symbiotic association with N-fixing
rhizobia, legumes sustain the production of protein-
rich seeds and fodder while improving productivity of
cereals and other crops in agricultural rotations
(Graham & Vance, 2003). These unique characteristics
make legume cultivation fundamental for sustainable
agriculture, improving environmental equilibrium
and quality of life. However, legume-rhizobia interac-
tion is often compromised by adverse environmental
conditions, mainly soil salinity and drought (Zahran,
1999). It is estimated that 60% of legume production
in the developing world occurs under conditions of
extreme drought stress (Graham & Vance, 2003). In
many countries belonging to the semiarid climate,
legume cultivation is in continuous regression because
of the low yield, and the needs are satisfied by
importation.

The symbiotic association and the plant-pathogen inter-
action represent two major types of plant-microorganism
interactions. In the early stages of both processes, the
response of the plant is very similar. The microorganism
finds the compatible host plant tissue (roots or leaves)
for attachment and commencement of the invasion
process. At this step, the plant defends rapidly by gener-
ation of reactive oxygen species (ROS). ROS include
superoxide radical (•O 2 − ), singlet oxygen ( 1 O 2 ), hydro-
gen peroxide (H 2 O 2 ) and the hydroxyl radical (•OH)
(Mylona & Polidoros, 2010). ROS are highly active mol-
ecules capable of oxidizing biomolecules including
proteins, lipids and nucleic acids (Ahmad et al., 2008,
2010, 2011, 2012, 2014, Ahmad 2014). ROS accumu-
lation orchestrates the initiation of plant antimicrobial
defences, facilitates the formation of cell wall barriers
preventing further spread of the microorganism, leads
to the induction of the hypersensitive response (HR),
and serves as a signal in secondary signalling pathways
that further activate defence responses. ROS, particu-
larly hydrogen peroxide, are considered to be the key
signals triggering plant responses to biotic and abiotic
stresses (Djébali et al., 2011; Ellouzi et al., 2011, 2013;
Mhadhbi et al., 2013; Bartoli et al., 2013).
In the case of symbiotic interaction a similar plant
response is initially triggered. Upon infection of a legume