Biotechnology approaches to overcome biotic and abiotic stress constraints in legumes - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 248

vegetarians and those in society who are unable to afford
expensive sources of protein like red meat (Day, 2013).
Being gluten free, legumes are the preferred alternative
to wheat and related staples (García-Manzanares &
Lucendo, 2011). On the ecological front, legumes are
involved in biological nitrogen fixation, which not only
leads to decreased demand for nitrogen input but also
helps in increasing net primary productivity, resulting
thereby in the production of useful chemical energy with
much less input of exogenous enrichment sources (Casler
et al., 2009; Jensen et al., 2012). Moreover, they form an
important part of permaculture systems, contributing
positively to nitrogen fixation and, hence, the nutrient
enrichment process (Bates & Hemenway, 2010). The
medicinal effects of the phytochemicals derived from
legumes are very important. These secondary metabolites
produced mainly as defence and signalling chemicals,
have been in human use for centuries due to their potent
health benefits (Muzquiz et al., 2012). Alkaloids, flavo-
noids, coumarins, anthraquinones, terpenes, glycosides
and lectins are some of the representative phytochemi-
cals derived from the members of this family(De Hoff
et al., 2009; Dixon & Pasinetti, 2010; Velazquez et al.,
2010; Kumar et al., 2012a; Spanou et al., 2012; Tiwari &
Pathak, 2013; Wink, 2013). These substances are used in
complementary and alternative medicine for the
treatment of cardiovascular, respiratory, urinary, meta-
bolic and nervous system disorders (Joshi et al., 2011).
Moreover, they formed the basis for the discovery and
development of many semisynthetic and synthetic drugs,
now employed in allopathic medicine (Hoareau &
DaSilva, 1999) (Figure 15.1).
One of the most important aspects of leguminous
plants is their ability to participate in the symbiotic rela-
tionship with the soil bacteria, rhizobia (Oldroyd, 2013).
On secretion of specific chemical signals from the root
nodules of the legumes, the rhizobia tend to convert
atmospheric nitrogen gas to the plant-consumable
forms, ammonia and ammonium compounds. This
mutualism helps in the nitrogen fixation process and
contributes positively to agriculture and ecosystems.
These bacteria are, therefore, included in a separate
class referred to as plant growth-promoting rhizo-
bacteria (PGPR). Legumes comprise many plant species,
including woody plants, ornamental plants, crops and
vegetables. Woody legumes grow in habitats across the
world, putting them among the preferred choices for
timber, firewood and construction material (Adams

Nitrogen
xation (77%
atmospheric
nitrogen)

Rich source
of medicinal
substances

High protein
content

Diverse
taxonomic
classes

Environmental
sustainability

Legumes

Architecture
design

Different plant
structures

Bioenergy

Figure 15.1 Importance of legumes in various sectors.

et al., 2010). Ornamental species, like Lathyrus odoratus
(sweet pea), can have wide variation in flower shape,
colour and other morphological characteristics, making
them conspicuous for pollination (Mikić et al., 2011).
The family Leguminosae has over 900 genera com-
prising around 23,000 plant species (The Plant List,
2010). Classified into three subfamilies, Mimosoideae,
Caesalpinoideae and Faboideae (Papilionoideae), based
upon their morphological characteristics, these plants
are distributed widely throughout the globe. Members
of the Mimosoideae are woody shrubs and vines,
distributed mainly in the warm and tropical regions of
the Americas and Asia. Acacias (Bouchenak-Khelladi
et al., 2010), mimosas and members of the genera
Inga and Pentaclethra are some of the most important
plants of this subfamily. The other two subfamilies,
Caesalpinoideae and Faboideae, follow a cosmopolitan
geographical distribution and are found globally in
tropical and subtropical regions. Both these subfamilies
contain chiefly woody shrubs and trees; however, the
Faboideae contains a number of non-woody annual
herbs as well (Łotocka et al., 2012). It has the largest
number of genera of the three subfamilies and includes
Lathyrus spp., Medicago spp., Lotus spp. and Astragalus
spp. The Caesalpiniodeae is most diverse in terms of
morphology and biogeographical distribution (Bruneau
et al., 2001). A number of leaf, flower and stem types are
seen in this group, and the presence of its members in
all regions of the world makes them the representative
timber and ornamental species of the family, with char-
acteristics of the other two subfamilies as well. Genera
in the Caesalpinoideae include Gleditsia , Amherstia ,
Gymnocladus , Delonix , Bauhinia , Caesalpinia and Senna .