Genetic and molecular responses of legumes in a changing environment - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 200

important role as sources of bioenergy. The woody
legumes have been used for building and fuel (Rangan,
2013). Certain varieties have a very distinctive appear-
ance and are utilized as ornamental plants (Ganguli &
Kennedy, 2013).
Legumes also contribute to ecosystems. They form
symbiotic relationships with many bacterial species and
help in fixing atmospheric nitrogen. These bacteria,
belonging to the rhizobacterial group, establish relation-
ships with the roots of leguminous plants. The plant
provides shelter and nutrients to the bacteria while the
bacteria help in converting the nitrogen into a usable
form for the plant, thereby, increasing the fertility of soil
and promoting the growth of legumes (Qadri et al., 2013).
Another group of rhizobacteria also helps the plants to
survive environmental stress conditions. These bacterial
species are collectively referred to as plant growth pro-
moting rhizobacteria (PGPRs) (Ram et al., 2013).
Hence, legumes are important for the livelihood of a
large human and animal population associated with the
agriculture sector. Their significance as a food source, as
a fuel and in medicinal systems makes them an impor-
tant subject for plant biotechnology. Any threat to plant
health can have significant outcomes in terms of finan-
cial losses and an increased burden on the biosphere. An
understanding of the various environmental threats fac-
ing leguminous plants is, therefore, essential. Moreover,
the study of the various genetic and molecular responses
to these threats is also of vital importance as the manip-
ulation of these factors can help in developing more
stress-resistant legume varieties.

(Jha et al., 2014). These abiotic stress factors greatly
promote attack by biological agents; for instance, water-
logging is a fundamental cause of fungal and bacterial
infections in leguminous plants (Lipiec et al., 2013).
Among the environmental factors, changes in soil
characteristics cause alterations in the growth patterns
of legumes. Increased acidity, and elevated salt and
metal concentrations can all have detrimental effects on
plant health. Usually, these stress factors do not work in
isolation to affect the plants; rather they initiate a com-
plex cascade of events that cause damage to the plant.
For example, heat along with saline soil results in
increase in the transpiration rate and absorption of more
water through the roots. The absorbed water contains a
higher proportion of salt, causing the plant to be salt
stressed. Similarly, a diminished supply of water to the
plant leads to osmotic stress in legumes. This causes a
reduced growth rate of the plant. The exposure of plants
to sudden changes in temperature leads to a diminished
ability to carry out normal life processes. Legumes can
easily tolerate slight increases and decreases in tempera-
tures (Gupta et al., 2014). However, when there is a
significant rise or fall in temperature, these plants fail to
tolerate these changes and are subject to either tissue or
organ loss leading, sometimes, to the death of the plant.
Cold season legumes like lentils, beans and peas are
sensitive to temperature rises (Cannon, 2013; Kumar
et al., 2013a). Warm season legumes like groundnut and
mung bean, if subjected to a sudden fall in temperature,
also suffer considerable damage (Hamidou et al., 2013;
Li et al., 2014). Among other environmental factors,
exposure to high-intensity light, high wind speeds and
natural disasters are significant causes of decreased
legume output.
These physical stress factors increase the susceptibility
of legumes to infestation with biotic pathological agents,
resulting in decreased yield of the plant and a significant
fall in the nitrogen-fixing capability of these plants
(Lipiec et al., 2013). These can, therefore, be classified as
a part of a complex 'stress matrix' that results in a mul-
tifactorial constrained state (Mittler, 2006). Plants tend
to respond to these stress factors in a variety of ways.
These responses usually involve upregulation of certain
genetic elements followed by the production of regulatory
and effector response elements (Duque et al., 2013;
Libault, 2013; Lindemose et al., 2013). The specific or
non-specific pathways activated against a particular stress
factor involve a number of chemicals, biomolecules and

12.3 environmental threats to
legumes

Legumes, like other plants, are exposed to a variety of
stimuli. Among these, both biotic and abiotic stress
factors have been associated with adverse effects on the
plants' health. Biotic stress factors include viruses,
bacteria, fungi, nematodes, weeds and herbs (Ansi et al.,
2010; Bhatnagar-Mathur et al., 2012; Boudreau, 2013).
Among the physical constraints, changes in climatic
conditions, and edaphic and geographical factors are of
prime importance (Duque et al., 2013). Moreover,
changes in temperature, altered availability of water to
the plant, and variation in the quantities of solutes and
other nutrients in the soil directly affect plant growth