Nutrient deficiencies under stress in legumes: An overview - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 61

high contents of sulphur-containing amino acids (legu-
min and PA1 respectively) was reduced in seeds from
plants grown under conditions of sulphur deficiency.
On the other hand the production of viclin (a non-sul-
phur-containing protein) was increased in seeds
produced after a long period of sulphur deficiency.
Furthermore, these authors also showed that relative
abundance of sulphur and nitrogen affects the produc-
tion of some proteins like sulphate transporter, APR,
sulphite reductase (SiR), oligoadenylate synthetase
thiollyase (OASTL), serine acetyltransferase (SAT) and
S-poor storage protein β-subunit of β-conglycinin.
They proposed that OAS is a key indicator of the
relative abundance of sulphur and nitrogen and their
application results in the increase in mRNAs encoding
for the above-mentioned proteins. In another
experiment by Steven et al. (2002), it was shown that
there is a significant increase in the concentration of
arginine in plants grown under sulphur deficiency,
which again supports the idea that sulphur deficiency
increases the amount of non-sulphur proteins. These
researches clearly demonstrate that nutritional defi-
ciencies have a direct impact on storage proteins of
legumes.

which include both enzymatic and low-molecular-
weight non-enzymatic antioxidant systems (Nobuhiro &
Mittler, 2006; Ahmad et al., 2010). Under water and
salinity stress increased activities of antioxidant enzymes
are well documented (Sairam & Srivastava 2002;
Ahmad et al., 2008, 2012; Iqbal & Bano, 2009; Khan &
Naqvi, 2010; Li et al., 2011; Chang et al., 2012; Weisany
et al., 2012). Rhizobia in the nodules of legumes are
slightly more resistant to drought/salt stress than the
plants themselves, thereby enhancing resistance to
water and salinity stresses (Serraja et al., 2008). However,
under severe stress nitrogen metabolism is reduced to a
great extent.
Plants, including legumes, accumulate several com-
patible solutes to maintain water content of the cell. An
experiment was carried out on chickpea in which it was
subjected to drought for 3, 5 and 7 days. There was a
decrease in leaf production, shoot elongation and bio-
mass, along with an increase in proline accumulation.
Proline is an alpha-amino acid that serves as a catalyst to
many organic reactions (Verbruggen & Hermans, 2008;
Macar et al., 2008; Szabados & Savoure, 2010).
Photo-inhibition is the light-induced reduction in the
photosynthetic activity of a plant; the extent of light
energy absorbed and used in photochemical processes
has a direct link with photo-inhibition, which increases
under water stress and in turn limits CO 2 assimilation.
Stress-induced stomatal closure limits CO 2 availability
for carboxylation resulting in excessive excitation of
photosystem II (PSII) and hence reducing its efficiency.
The protective mechanisms that legumes have evolved
in order to minimize these effects are:
1 non-photochemical energy dissipation;
2 movement of chloroplasts;
3 change in chlorophyll concentration;
4 increase in ROS capacity;
5 paraheliotropism (leaf movement).
The extent of paraheliotropism increases with a decrease
in water potential, decrease in light interception and
maintenance of a high percentage of PSII reaction cen-
tres (Pastenes et al., 2005).

3.8 protective mechanisms triggered
in legumes under stress

3.8.1 Drought and salinity stress
Drought and salinity are serious environmental prob-
lems restricting legume plant productivity (Gaur et al.,
2008) by affecting photosynthesis and respiration
(Kaiser, 1987; Chaves, 1991). Overall changes induced
in physiology and biochemistry of plants under water
and salinity stress are usually attributed to:
1 Reduction in leaf size, stem extension and root
proliferation.
2 Reduced water use efficiency (WUE) and hence
altered plant-water relations.
3 Decreased nodule activity and hence nitrogen
metabolism.
4 In addition, salinity causes specific ion toxicity due to
accumulation of sodium, chloride, and/or boron in
the tissue to damaging levels.
Increased production of ROS results in oxidative
stress (Foyer & Noctor, 2003; Ahmad et al., 2010). Plants
are well equipped with antioxidant defence systems,

3.8.2 Cold stress
Legumes adapt to stresses by changing their metabolic
rates, protein synthesis, osmolytes and gene expres-
sion. Cold stress is a climatic condition in which the
temperature is so low that it harms the normal metab-
olism of the legume. Low temperatures disturb the