Exogenous application of phytoprotectants in legumes against environmental stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 162

glutathione (GSH), phenolic compounds, alkaloids,
non-protein amino acids and α-tocopherols. Antioxidant
enzymes are superoxide dismutase (SOD), catalase
(CAT), ascorbate peroxidase (APX), glutathione reduc-
tase (GR), monodehydroascorbate reductase (MDHAR),
dehydroascorbate reductase (DHAR), glutathione per-
oxidase (GPX), guaicol peroxidase (GOPX), peroxidase
(POD) and glutathione- S -transferase (GST) (Hasanuz-
zaman et al., 2012a). Polyamines (PAs), aliphatic amines
and organic polycations have been recognized as regula-
tors of plant metabolism for over 100 years, for their
roles in cell proliferation, somatic embryogenesis, seed
germination, growth, morphogenesis, differentiation,
reproductive development, fruit set and programmed
cell death (Kusano et al., 2008; Hussain et al., 2011).
Osmolytes or osmoprotectants, like proline (Pro) and
glycine betaine (GB), are organic metabolites that play
potential protective roles against stresses (Ashraf &
Foolad, 2007; Chen & Murata, 2008). Different signal-
ling molecules have emerged in connection with
redox-regulated or defense-related gene expression
involved in establishing plant stress tolerance (Sung &
Hong, 2010). Some trace elements have been identified
as not only promoting growth and development of
plants but also increasing resistance to certain abiotic
stresses (Feng et al., 2013). The roles of phytohormones,
amino acids, antioxidants, signalling molecules and
trace elements in overcoming stress effects on plants or
in developing abiotic stress resistance in plant species
have been studied by many research groups. But the
complexities of the species-specific and stress-specific
mechanisms in plants mean that much more research
is needed.
This chapter presents a comprehensive review
regarding the responses of legumes to common envi-
ronmental stresses, and the roles of different groups of
compounds or molecules like phytohormones, amino
acids and derivatives, antioxidants, signalling molecules
and trace elements, in mitigating the effects of stress in
legumes.

system. The latter property makes them different
from other crops because they not only provide
food and feeds but also can act as potent agents to
enrich soil fertility. These and other benefits of
legume crops mean that more than 200 species of
legumes are known to be cultivated worldwide,
including: herbs (e.g. Lens culinaris , Pisum sativum ,
Phaseolus vulgaris ), shrubs ( Gliricidia sepium,
Calliandra calothyrsus, Sesbania sesban and S. grandi-
flora) and trees ( Sesbania grandiflora , Moringa oleifera ,
Leucaena leucocephala ). Some of the major pulses are
presented in Figure 11.1.
Globally, legume crops (pulses) are the third most
important group of crops after cereals and oilseeds.
Developing countries are the major source of pulses,
contributing 74% of total production (Khedar et al.,
2008). Pulses play an important role in human diets
as well as enriching soil fertility, and hence are a
major contributor to food security and sustainable
agriculture. Nearly 70% of pulses are used for food,
mostly in developing countries; 25% are used for
feed, mostly in Europe, the Commonwealth of
Independent States and Australia; the remaining 5%
go for seed and other purposes (Khedar et al., 2008).
Being a rich source of protein, minerals, vitamins,
crude fibre and several amino acids required for
human health, pulses are considered as a health food
and offer security against protein malnutrition to
millions of people in the developing world. The
nutritional compositions of some major pulses are
depicted in Table 11.1.
Pulses are a 'wonderful gift' of nature for all living
beings, for the soil, and for natural resources and the
environment. Every plant of a pulse crop may be
called a 'mini N factory' because with the help of
Rhizobium bacteria, pulses fix atmospheric N 2 and so
improve soil fertility (Figure 11.2). Legumes are pos-
sibly the most important cultivated crops capable of
fixing carbon and N. In many areas, legumes are cul-
tivated as cover crops after the harvest of main crops,
first, because they provide economic benefit and, sec-
ond, they increase the fertility by fixing atmospheric
N. Pulse crops can fix 30-200 kg N ha −1 year −1 (Khedar
et al., 2008; Table 11.2). Hence, pulse crops sustain
the productivity of the soil and make the soil eco-
nomically more sound and environmentlly more
friendly.

11.2 Importance of legumes

Legumes are plants belonging to the family Fabaceae
(formerly known as Leguminosae) that bear their
seeds in pods and contain nodules on their root